Questions and Answers
Which classes of vertebrates are generally considered fish?
What percentage of known fish species are found in marine environments?
What is the smallest unit in the hierarchical classification of organisms?
Which environment hosts the highest number of fish species according to the document?
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In binominal nomenclature, how is the genus name presented?
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How many species are estimated to inhabit the cold polar waters?
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Which of the following is true regarding fish species distribution?
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What is the proper classification hierarchy from species to kingdom?
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What is the primary reason scientific names should be used in publications?
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Which group of fish is classified as having a high urea content in muscle?
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What distinguishes demersal fish from pelagic fish?
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How do fish muscle cells differ from those of terrestrial mammals?
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What is the role of the myocommata in fish anatomy?
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Which factor causes dark muscle to be more prevalent in pelagic fish?
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What type of muscle tissue is predominant in most fish?
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Why is the presence of lipids significant in the muscle tissue of fish?
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Which pigment is responsible for the reddish color in salmon and sea trout?
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Which classification group contains jawless fish?
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What anatomical feature runs the full length between two myocommata in fish?
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What is the distinctive characteristic of bony fish muscles compared to cartilaginous fish muscles?
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Which statement about false ribs in fish is true?
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Where do the longest muscle cells in cod typically occur?
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What is the recommended bleeding period for fish before they are gutted?
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What complication arises from the two-step procedure of bleeding followed by gutting?
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Which factor is most critical for achieving the best bleeding results in fish?
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What did Huss and Asenjo find about the cutting method for optimal bleeding?
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Which organs in fish are recognized as major foodstuffs?
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What changes occur in cod muscle prior to spawning?
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At what stage do most fish become sexually mature?
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Which fish species is known to only migrate once before degenerating and dying?
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What happens to the lipid content during migration in Pacific salmon?
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How does the growth process affect muscle cells in fish?
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Which of the following statements relates to the weight of a fish prior to spawning?
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What is a secondary effect of rough handling of fish during capture?
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What occurs to fish reserves during gonadal development?
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What is the lifespan of North Sea cod in relation to spawning?
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What is one key attribute of the fish heart's design?
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What is the primary reason for including astaxanthin in fish feed during aquaculture?
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What is the role of Ca++ in muscle contraction according to physiological processes described?
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Why do salmonids living in waters with little carotenoid exhibit less red muscle color?
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What is a major difference between light muscle and dark muscle in fish?
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What happens to muscle fibers when ATP levels reach a minimum post-mortem?
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How does the cardiovascular system of fish differ from that of mammals?
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What occurs during blood circulation in a fish after blood passes through the gills?
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How does the blood volume distribution in fish relate to muscle tissue?
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What physiological function primarily prevents counterflow of blood in fish veins?
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What is the consequence of inadequate carotenoid ingestion in fish from low-carotenoid waters?
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Why is muscle contraction important for blood circulation in fish?
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What happens to lactic acid produced in light muscle during anaerobic metabolism?
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What physiological change occurs in fish muscle at spawning time?
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What is the effect of post-mortem conditions on the ATP levels in fish muscle?
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What occurs to fish muscle immediately after death?
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How does high temperature affect rigor mortis in cod?
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Which factor does NOT affect the rate of onset and resolution of rigor mortis in fish?
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What is the typical duration of rigor mortis after it begins?
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What phenomenon may occur due to strong rigor tensions in fish?
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What effect does cooler storage temperature have on the onset of rigor mortis in some tropical fish species?
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Which of the following statements is true regarding sensory changes in fish during storage?
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Why is it generally accepted that the onset and duration of rigor mortis occur more rapidly at higher temperatures?
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What is the primary factor that differentiates firm and elastic flesh from soft flesh in fish?
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What happens to the pH of cod muscle post-mortem as anaerobic glycolysis occurs?
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What visual characteristics indicate a fresh fish's eyes?
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How do enzymatic changes in fish affect freshness compared to bacterial spoilage?
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What is indicated by a yellowish color in the gills of fish?
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In what condition is the flesh of fish described as velvety or waxy?
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What is the consequence of oxygen deprivation in fish muscle immediately post-mortem?
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What does a score lower than 4 signify on the sensory evaluation scale for fish?
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What type of respiration is primarily responsible for ATP production after a fish dies?
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What indicates that the kidneys and organ residues in fish have started to spoil?
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Which sensory characteristic should be present in the gills of fresh fish?
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Which of the following best describes the flesh condition when it sticks to the peritoneum?
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What end-products are generated from anaerobic metabolism during fish post-mortem?
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Which factor strongly influences the degradation rate of chilled fish compared to ambient conditions?
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What is the effect of stunning and killing fish by hypothermia on the onset of rigor mortis?
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What occurs to muscle fibers after ATP levels fall post-mortem?
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How does the texture of fish change when cooked post-rigor compared to pre-rigor?
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What is the expected change in length of dark muscle when cooked pre-rigor?
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Which phase characterizes the very fresh fish with a sweet taste after catching?
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What impact does rough handling of fish during capture have on fileting yield?
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How does the state of glycogen reserves affect the onset of rigor mortis in fish?
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Which of the following factors primarily affects the sensory evaluation of raw fish?
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What happens to fish fillets if they are frozen pre-rigor and then thawed at low temperatures?
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What occurs during Phase 3 of fish spoilage?
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Which species demonstrates the shortest time from death to onset of rigor when stressed?
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What is a characteristic change in fish that is very fresh when compared to stored fish?
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What does the term 'post-rigor' refer to in the quality of fish?
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When evaluating cooked fish, which phase indicates the first signs of spoilage?
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What is the typical pH range observed for large mackerel during rigor mortis?
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How does stored glycogen in fish generally compare to that in mammals?
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What effect does pre-capture stress have on the pH levels of fish muscle?
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What is indicated by a high 'K' value in the context of fish freshness?
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What is the role of ATP in muscle contraction?
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Why are fish in rigor mortis unsuitable for processing?
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What does the breakdown of ATP in post-mortem fish muscle indicate?
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Which nucleotide is associated with the desirable fresh fish flavor?
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What happens to the water-holding capacity of fish muscle as post-mortem pH drops?
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According to the autolytic changes after death, which compound is one of the first to degrade?
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What does the term 'rigor mortis' refer to in fish muscle?
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What is a consequence of muscle tissue being in rigor mortis during processing?
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Which factor does NOT affect the levels of stored glycogen in fish before death?
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What occurs during the resolution of rigor in fish muscle?
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What is the role of the TMAO-ase enzyme in fish?
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What can minimize the production of formaldehyde during frozen storage of fish?
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Which organ in gadoid fishes is primarily associated with the presence of TMAO demethylase?
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What impact does rough handling of fish during capture have on their quality?
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The softening of tissue due to collagenases is primarily associated with which factor?
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Which of the following statements about the production of formaldehyde in fish is accurate?
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What is one critical factor in preventing 'gaping' of fish fillets during storage?
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In terms of muscle activity, how does dark muscle differ from white muscle in gadoid fish?
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What is a recommended practice to minimize the toughening of hake muscle during frozen storage?
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Which enzyme class is responsible for the softening of connective tissues in fish?
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What is indicated by the equal rates of formation and breakdown of IMP in sterile and non-sterile cod tissue?
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What effect does physical handling have on autolytic changes in chilled fish?
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What role does bacterial nucleoside phosphorylase play in refrigerated cod?
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Which enzyme is primarily responsible for the degradation of ATP through to inosine?
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What is a consequence of the autolysis of fish muscle tissue?
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Which factors primarily influence belly-bursting in herring?
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What characteristic is associated with the cathepsins found in fish tissues?
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What is the effect of autolytic proteolysis on pelagic fish during the summer months?
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Which of the following is NOT a factor in the rates of nucleotide degradation among different fish species?
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Which proteolytic enzymes have been investigated for their role in fish tissue breakdown?
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Which process can inhibit proteolysis in fish muscle tissue?
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What pH range do cathepsin D enzymes predominantly exhibit activity?
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What was a significant finding related to nucleotide breakdown rates in bulk-stored herring for fishmeal?
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Why is it important to store iced fish in boxes that are not deeper than 30 cm?
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Which statement is true regarding the activity of cathepsins in fish tissues?
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What is the primary reason cathepsin L is implicated in the softening of salmon muscle during spawning?
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Why is it unlikely that Reddi's enzyme was active in salted fish products?
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How does freezing and thawing affect autolytic enzyme activity in fish muscles?
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Which enzymes are primarily responsible for the post mortem autolysis of meat?
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What effect does cathepsin L activity have on muscle texture during the fermentation process of fish products?
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Which type of collagen has been linked to the gaping or breakdown of myotomes during long-term storage of fish?
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How does calpain activity in fish compare to that in mammalian muscle?
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What is the significance of calcium in the activity of calpains?
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Which statement accurately describes the role of collagenases in fish?
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What happens to tropical fish species in terms of calpain autolysis compared to those adapted to colder environments?
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Which major consequence does high calpain activity have on the quality of fish muscle?
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What is a significant factor influencing calpain activity in fish species?
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What is one of the attributes of proteolytic enzymes in parasitized Pacific hake muscle?
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What notable difference exists between myosins in fish and mammals concerning calpain action?
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What is the first sensory change in fish during storage?
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What condition does fish undergo immediately after death?
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How does high temperature affect the onset of rigor mortis in cod?
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Which factor does NOT affect the rate of onset and resolution of rigor mortis?
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What physiological change occurs in the fish muscle after rigor mortis resolves?
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What is the relationship between temperature and the onset of rigor mortis in certain tropical fish?
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What can be a consequence of strong rigor tensions in fish?
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What does the onset of rigor mortis depend on in carp, according to research?
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What effect does stress have on the onset of rigor mortis in fish?
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How does the method of stunning affect rigor mortis in fish?
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What happens to muscle contraction when fish are filleted pre-rigor?
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Which of the following best describes the texture of fish cooked post-rigor?
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What does the onset time of rigor mortis depend on?
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What phase indicates the fish has become spoiled and putrid?
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What is the effect of cooking fish in rigor compared to cooking pre-rigor?
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During which phase does the fish begin to lose its characteristic odour and taste?
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What is the maximum shrinkage of dark muscle according to the content?
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What happens during the cooking of fillets removed pre-rigor?
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What condition indicates a fish is in a ‘1’ state for flesh inspection based on its surface characteristics?
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Which of the following statements about the appearance of fish before and after storage is true?
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In the context of fish freshness, which gill condition would indicate a decline in quality?
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Which assessment method should be conducted to determine the quality of chilled fish during storage?
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Which aspect of the fish's visual inspection should be evaluated first for overall quality assessment?
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Which of the following factors is NOT relevant when assessing the condition of the fish's flesh?
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What is the correct pH range of cod muscle during post mortem changes?
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What physiological change occurs in fish muscle tissue shortly after death?
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Which of the following is a characteristic of autolytic changes in fish spoilage?
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How does internal energy production in fish muscles occur after death?
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Which of the following pathways is NOT involved in ATP production in post mortem fish muscle?
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What happens to the freshness indicators of fish when they fall below a sensory evaluation score of 4?
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What characteristic is used to describe a ‘1’ state in the eye inspection of fish?
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What is the significance of the bright red color of the kidneys and other organs in fish?
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What effect does rigorous post mortem handling have on fish tissue?
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What is the primary enzyme responsible for autolysis in salmon muscle during spawning?
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How does sodium chloride (NaCl) affect enzyme activity in the context of fish muscle?
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Which statement best describes the relationship between cathepsin L activity and the texture of fish muscle?
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What role do calpains play in the texture changes of fish muscle?
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Which factor is most likely to enhance autolytic activity in fish muscle during storage?
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What is the effect of high temperature on connective tissue in fish muscle?
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What distinguishes fish calpains from mammalian calpains?
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Which enzyme is implicated in the jelly-like softening of flounder muscle?
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What is a primary characteristic of the degradation process mediated by collagenases in fish muscle?
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What are the primary conditions that activate calpains in fish?
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What is the effect of the presence of catheptic enzymes on fermented fish products?
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In terms of fish autolysis, how do myofibrillar proteins contribute to muscle texture?
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What role does the degradation of type V collagen play in the texture of fish muscle?
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What is the primary enzyme responsible for the toughening of frozen gadoid fish?
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Which factor significantly accelerates the breakdown of fish flavor due to nucleotide degradation?
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How can toughening of frozen fish muscle be minimized during storage?
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What change occurs in chilled prawns due to collagenase enzymes?
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What is the byproduct of TMAO breakdown that poses a greater commercial significance?
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In which tissue is TMAO demethylase most commonly found?
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What condition leads to high levels of formaldehyde production in frozen fish storage?
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What is a consequence of the physical disruption of muscle cells in fish?
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How does dark muscle differ from white muscle in terms of TMAO demethylase activity?
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Which of the following is NOT a factor involved in autolytic changes affecting fish edibility?
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What is the main factor that influences the ultimate post mortem pH in fish?
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Which fish species is noted for having particularly low ultimate rigor pH levels?
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What happens to the muscle protein's water-holding capacity as post mortem pH decreases?
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What happens to fish muscle as rigor mortis sets in?
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What is associated with the undesirable texture of fish muscle when the pH is low?
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How does bleeding fish affect lactic acid production post mortem?
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What is the consequence of a fish being stressed prior to capture in terms of its pH level?
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Which nucleotide catabolite is primarily associated with the desirable flavor of fresh fish?
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What aspect of nucleotide degradation is considered unreliable for measuring fish freshness?
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What is the primary role of ATP in muscle contractions?
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Which change is NOT typically observed in fish muscle during autolysis?
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What enzyme is primarily involved in muscle contraction and is affected during rigor mortis?
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What can significantly affect the physical properties of fish muscle post mortem?
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Which enzyme is primarily responsible for the conversion of Iino to Hx in non-sterile cod samples?
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What is the main consequence of physical handling on chilled fish?
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What effect do autolytic processes have on fish used for fishmeal production?
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What is a notable consequence of belly-bursting in pelagic fish species?
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Which factor was found to influence belly-bursting in herring the most?
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What is the primary role of cathepsins in fish tissue?
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What impact does autolysis have on the nutritional value of fish?
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What is one method that has been shown to inhibit proteolysis in fish?
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How does the activity of proteolytic enzymes change after physical abuse to fish?
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How does the degradation of nucleotide catabolites differ between sterile and non-sterile cod fillets?
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What is a key reason to avoid stacking fish boxes too deeply?
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What pH range is cathepsin D believed to be active in?
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What describes the compartmentalization of autolytic enzymes in fish tissues?
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What was a significant finding in the study carried out by Surette et al. (1990)?
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What is significantly impacted by temperature changes in the range of 0 to 25°C?
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Which temperature condition results in minimal growth for many bacteria?
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What is the primary reason for extending the shelf life of fish products?
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What is the impact of storing fresh fish in ice at 0°C?
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What does the relative rate of spoilage (RRS) depict with regard to fish storage?
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At which temperature do many bacteria begin to have significantly reduced growth rates?
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Why do psychrotrophic organisms show slow growth at low temperatures?
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In industrialized countries, how is fresh fish typically preserved at low temperatures?
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What effect does temperature have on the relative rate of spoilage (RRS) of seafood products?
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Which microflora are primarily responsible for seafood spoilage at low temperatures (0-5°C)?
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Which spoilage model is suggested by Ratkowsky et al. for sub-optimal temperatures?
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What is the predicted relative rate of spoilage (RRS) for typical tropical fish stored at 25°C compared to 0°C?
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What is the effect of temperature history in fish storage as indicated by temperature loggers?
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What happens to the RRS of packed fresh fish and superchilled fresh fish products?
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Why was the Arrhenius Equation deemed inaccurate for predicting spoilage rates?
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Which temperature range hosts the highest variety of spoilage species for fish?
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What cumulative effect does temperature have on seafood effectively predicted by spoilage models?
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What is the theoretical minimum temperature for growth of psychrotrophic bacteria according to research?
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Which factor limits the practical usage of electronic time/temperature function integrators for predicting RRS?
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Which of the following spoilage models incorporates a relative rate concept?
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Which organism primarily causes spoilage at elevated temperatures (15-30°C)?
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What negative effect has been observed with superchilling certain fish species?
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How does the temperature affect the percentage of frozen water in superchilled fish?
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What conclusion can be drawn about the importance of hygiene during onboard handling of fish?
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What was observed regarding the organoleptic quality of fish after different handling procedures?
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What factor significantly affects the shelf life of superchilled shrimp compared to cod?
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Which storage temperature led to increased drip loss in superchilled cod?
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What has been suggested regarding the construction of fish boxes for chilling purposes?
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Which method has been considered for prolonging storage life by reducing bacterial counts?
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What relationship was established between bacterial contamination and fish storage life?
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What effect does lowering the pH have on muscle proteins in fish?
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What was the observed impact of the superchilling technique on mackerel storage at -3°C?
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What is the primary impact of temperature on the shelf life of fish products?
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Which of the following statements is true regarding the effects of RSW storage?
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Which fish products are noted as having increased drip loss when stored in high CO2 concentrations?
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What is a significant negative effect of storing fish in 100% CO2?
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Why is it challenging to unload fish when heat exchanges are used on vessels?
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Which factor does NOT influence the rate of spoilage in fish?
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How does the demerit point system relate to fish quality assessment?
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What is a consequence of the ice crystals formed during superchilling in fish?
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How does the addition of CO2 to refrigerated seawater (RSW) influence the shelf life of pink shrimps?
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What has research indicated about the sensory quality of fish stored using superchilling methods?
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What is the effect of exposure to high temperatures before chilling on white-fleshed fish?
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What is a common problem associated with CO2 in RSW systems?
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What is superchilling in fish storage?
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Which of the following bacteria is noted to exhibit increased toxin production in anaerobic conditions?
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Which equation is used to determine the shelf life of fish at different temperatures based on initial quality?
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What happens to fish that are not gutted before storage?
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What impact does CO2 have on the color of fish stored in high concentrations?
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What is a common effect of lipid oxidation in fish?
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What was the suggestion made by Spencer and Baines regarding fish spoilage?
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How does the production of TMA in fish products during MAP compare to traditional storage methods?
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What role does the Frigido-system serve in fish storage?
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Why has modified atmosphere packaging (MAP) found less practical application with fish products compared to meats?
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What is primarily affected by CO2 levels in fish storage?
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Which temperature range is associated with the square root spoilage model?
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What is a major consequence of delayed chilling for fatty fish?
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For which type of fish is the negative impact of CO2 on color and texture less critical?
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How does the storage system using refrigerated sea water (RSW) benefit fish storage?
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What is the best description of the overall effect of CO2 on fish stored in RSW?
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What common problem occurs when white-fleshed fish are not chilled properly?
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What is a consequence of the strong digestive enzymes present in fish prior to gutting?
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What importance does initial product quality hold in temperature spoilage models?
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What is the approximate shelf life range of tropical marine fish when stored in ice?
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Which fish type has the longest shelf life according to the provided data?
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Which of the following species has a shelf life that exceeds 20 days when stored in ice?
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Which factor significantly influences the shelf life of fish in iced storage?
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Which species has the shortest shelf life in ice according to the data provided?
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What is the primary bacterial group responsible for spoilage in iced stored fish?
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Which characteristic is used to differentiate spoilage between temperate and tropical fish?
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Which marine fish species can last between 21 and 26 days in iced storage?
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What role does pH play in the shelf life of fish?
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What common misconception may arise regarding the spoilage rates between tropical and temperate fish?
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What aspect of tropical fish spoilage has been proposed as having less impact than previously thought?
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What is a notable biochemical characteristic of spoilage in Shewanella-dominated fish?
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What is often observed about the shelf life of freshwater fish compared to marine species?
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What conclusion did Lima dos Santos reach regarding the shelf life of temperate versus tropical fish?
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What effect does high CO2 concentration have on microbial growth in food products?
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Which method has been shown to effectively extend the shelf life of fish?
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What is a primary concern of using chlorinated water for washing fish?
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What types of microorganisms dominate the spoilage of vacuum packed (VP) meat products?
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Why does modified atmosphere packaging (MAP) have limited effect on the shelf life of fresh fish?
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What happens to the pH level of fish flesh stored in CO2 packed conditions?
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Which of the following fish species is generally better suited for MAP storage?
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What is the spoilage organism primarily responsible for packed cod spoilage?
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What common reaction is caused by the metabolic activity of Photobacterium phosphoreum in spoiled fish?
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How does the spoilage microflora differ between meat and fish?
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What is the primary reason that washing fish in clean seawater is conducted?
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What characteristic of Photobacterium phosphoreum affects cod shelf life?
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Study Notes
Fish Overview
- Defined as aquatic vertebrates using gills for oxygen and fins with fin rays.
- Major fish groups include cartilaginous fishes (sharks and rays) and bony fishes.
- Over 20,000 fish species exist, with 58% found in marine environments.
- Warm and temperate waters host around 8,000 species; only 225 species inhabit the open ocean.
Taxonomy of Fish
- Taxonomy classifies fish based on evolutionary relationships.
- Scientific names follow binomial nomenclature, comprising genus and species (e.g., Delphinus delphis for common dolphin).
- Common names can cause confusion due to regional variations.
Classification by Characteristics
- Fish are categorized into:
- Cyclostomes: jawless fish (lampreys, slime-eels).
- Chondrichthyes: cartilaginous fish (sharks, rays) with high urea content.
-
Teleostei: bony fish, further divided into:
- Pelagic fish (fatty: herring, mackerel).
- Demersal fish (lean: cod, haddock).
Anatomy and Physiology
Skeleton
- Fish possess a vertebral column (backbone) and cranium.
- Backbone is segmented into vertebrae with neural spines; ribs may vary from cartilaginous to bony.
Muscle Anatomy and Function
- Fish muscle lacks tendons, consists of parallel muscle cells (myotomes) connected by connective tissue (myocommata).
- Dorsal and ventral muscle parts differ in fiber lengths and diameters.
- Dark muscle, rich in lipids and myoglobin, is more prevalent in active pelagic species.
Muscle Contraction
- Contraction initiated by nervous impulses releasing Ca++, activating ATP-ase for muscle fiber contraction.
- Dark muscle has higher energy; utilizes aerobic metabolism, while light muscle relies on anaerobic metabolism.
Cardiovascular System
- Fish heart operates on a single circulation system with two chambers.
- Blood is pumped to gills for oxygenation, then distributed to the body.
- Fish blood volume is 1.5-3.0% of body weight; primarily in internal organs.
Bleeding and Handling
- Bleeding fish post-capture can enhance fillet quality.
- Recommendations vary on bleeding methods and times to limit discoloration and ensure quality.
- Rough handling can lead to bruising and contamination of muscle tissues.
Growth and Reproduction
- Fish growth involves increasing muscle cell size, not quantity.
- Sexual maturity is generally size-dependent, reaching earlier in males.
- Gonad development takes energy, often occurring during low food intake.
Chemical Composition
- Varies by species, age, sex, environment, and season.
- Key constituents include protein, lipid, and carbohydrate percentages, with fish typically lower in protein than isolated beef muscle.
Sensory Changes in Fish
- Sensory changes relate to appearance, odour, texture, and taste of fish, crucial for assessing freshness.
- Rigor mortis begins immediately post-mortem, characterized by muscle stiffening, lasting for a day or more before resolving.
- Fish muscle starts soft and limp post-death, then becomes hard and stiff due to rigor mortis, followed by a relaxed, non-elastic state.
- Onset and duration of rigor mortis vary by species and are influenced by temperature, handling, and fish condition.
- High temperatures accelerate rigor mortis, while some tropical fish show a faster onset at 0°C.
- Stress and glycogen depletion at death hasten rigor mortis onset, with stunning methods significantly affecting timing.
- Pre-rigor filleting yields better quality; rigor mortis leads to stiff muscle and poor filleting yields.
- Post-rigor, fish flesh becomes firm and elastic, while cooking pre-rigor results in a soft texture.
Evaluation of Freshness
- Sensory evaluations consider appearance, texture, and odour, influenced by storage conditions.
- Fish stored without ice spoil faster but have less visible change than those stored in ice.
- Freshness changes can be categorized into four distinct phases:
- Phase 1: Fresh fish has a sweet, delicate taste; optimal taste observed 2-3 days post-catch.
- Phase 2: Loss of characteristic taste and odour; flesh still pleasant.
- Phase 3: Signs of spoilage with unpleasant odours; texture deteriorates.
- Phase 4: Fish is spoiled, exhibiting putrid characteristics.
Autolytic Changes and Energy Production
- Autolysis denotes "self-digestion," distinguishing between bacterial and enzymatic spoilage.
- Lack of oxygen post-mortem disrupts normal energy production in muscles, relying on anaerobic pathways which are less efficient than aerobic respiration.
- Depletion of ATP during rigor mortis results in stiff, inextensible muscle, complicating processing.
- pH drops during post-mortem glycolysis, affecting muscle properties; drops range from 6.8 to lower levels depending on species.
- Stress affects glycogen levels pre-capture, consequently altering post-mortem pH and quality.
Autolysis and Nucleotide Catabolism
- Rigor mortis onset correlates with a drop in ATP levels and degradation of ATP to AMP, IMP, and further derivatives.
- Autolytic changes follow a predictable pattern after death, affecting perceived freshness quality.
- Changes in ATP and its catabolites indicate spoilage but do not directly correlate with texture changes.
- The freshness index (K value) is useful, but variability among species makes it unreliable for all marine fish.### Hx Determination and Fish Species
- Hx determination is unlikely to be useful for species like swordfish and redfish due to their specific biological characteristics.
Autolytic Changes in Fish
- Physical handling accelerates autolytic changes in chilled fish, affecting edibility and filleting yields.
- Sterile fillets show a greater breakdown rate of nucleotide catabolites compared to non-sterile cod, indicating that autolytic enzymes are compartmentalized.
Importance of Handling Practices
- Storing iced fish in boxes over 30 cm deep or allowing stacking can exacerbate autolysis.
- Systems for moving fish must protect delicate tissues from physical damage.
Nucleotide Catabolite Analysis
- Rapid methods exist for determining individual nucleotide catabolites and freshness indices.
Proteolytic Enzymes and Fish Quality
- Autolytic proteolysis in fish leads to tissue softening, most notably in pelagic species like herring, especially during summer feeding, impacting commercial value.
- Autolysis can promote bacterial growth, worsening spoilage and lowering fish quality.
Cathepsins in Fish Autolysis
- Cathepsins, acid proteases stored in lysosomes, become active post-mortem after physical stress, leading to significant tissue breakdown.
- Cathepsin L is a major factor in muscle softening, with its activity correlated to the texture of fish muscle.
Effects of Freezing on Autolysis
- Freezing breaks cell membranes, releasing enzymes like cathepsins, enhancing autolysis and softening.
- Studies show cathepsin L activity is higher in frozen/thawed tissues compared to fresh, influencing the muscle's texture.
Calpains Role in Texture Changes
- Calpains, calcium-activated proteases, significantly contribute to fish muscle autolysis, particularly at physiological pH levels.
- Active at lower temperatures compared to mammalian counterparts, calpains contribute to texture softening during chilled storage.
Collagenase Effects on Fish Texture
- Collagenases weaken connective tissue in fish, leading to gaping in fillets and softening during storage.
- The breakdown of type V collagen correlates with textural degradation of fish tissue.
TMAO and Formaldehyde Production
- TMAO, regulated by bacterial action and intrinsic enzymes, can be converted into dimethylamine and formaldehyde, leading to detrimental toughening of fish muscle.
- Enzymes responsible for this reaction, especially in gadoid fishes, become active upon tissue disruption by freezing.
Prevention Strategies for Autolytic Changes
- Minimizing physical damage and maintaining low storage temperatures (< -30°C) can prevent toughening from autolytic actions.
- Importance of adhering to proper handling practices before freezing to maintain fish quality.
General Summary of Autolytic Changes in Fish
- Both physical disruption and environmental conditions play critical roles in the rate and extent of autolytic changes in fish.
- Key enzymes involved include glycolytic enzymes, autolytic enzymes for nucleotide breakdown, cathepsins, calpains, and collagenases, each with specific impacts on texture and quality.
Sensory Changes in Fish
- Sensory changes relate to appearance, odour, texture, and taste of fish, crucial for assessing freshness.
- Rigor mortis begins immediately post-mortem, characterized by muscle stiffening, lasting for a day or more before resolving.
- Fish muscle starts soft and limp post-death, then becomes hard and stiff due to rigor mortis, followed by a relaxed, non-elastic state.
- Onset and duration of rigor mortis vary by species and are influenced by temperature, handling, and fish condition.
- High temperatures accelerate rigor mortis, while some tropical fish show a faster onset at 0°C.
- Stress and glycogen depletion at death hasten rigor mortis onset, with stunning methods significantly affecting timing.
- Pre-rigor filleting yields better quality; rigor mortis leads to stiff muscle and poor filleting yields.
- Post-rigor, fish flesh becomes firm and elastic, while cooking pre-rigor results in a soft texture.
Evaluation of Freshness
- Sensory evaluations consider appearance, texture, and odour, influenced by storage conditions.
- Fish stored without ice spoil faster but have less visible change than those stored in ice.
- Freshness changes can be categorized into four distinct phases:
- Phase 1: Fresh fish has a sweet, delicate taste; optimal taste observed 2-3 days post-catch.
- Phase 2: Loss of characteristic taste and odour; flesh still pleasant.
- Phase 3: Signs of spoilage with unpleasant odours; texture deteriorates.
- Phase 4: Fish is spoiled, exhibiting putrid characteristics.
Autolytic Changes and Energy Production
- Autolysis denotes "self-digestion," distinguishing between bacterial and enzymatic spoilage.
- Lack of oxygen post-mortem disrupts normal energy production in muscles, relying on anaerobic pathways which are less efficient than aerobic respiration.
- Depletion of ATP during rigor mortis results in stiff, inextensible muscle, complicating processing.
- pH drops during post-mortem glycolysis, affecting muscle properties; drops range from 6.8 to lower levels depending on species.
- Stress affects glycogen levels pre-capture, consequently altering post-mortem pH and quality.
Autolysis and Nucleotide Catabolism
- Rigor mortis onset correlates with a drop in ATP levels and degradation of ATP to AMP, IMP, and further derivatives.
- Autolytic changes follow a predictable pattern after death, affecting perceived freshness quality.
- Changes in ATP and its catabolites indicate spoilage but do not directly correlate with texture changes.
- The freshness index (K value) is useful, but variability among species makes it unreliable for all marine fish.### Hx Determination and Fish Species
- Hx determination is unlikely to be useful for species like swordfish and redfish due to their specific biological characteristics.
Autolytic Changes in Fish
- Physical handling accelerates autolytic changes in chilled fish, affecting edibility and filleting yields.
- Sterile fillets show a greater breakdown rate of nucleotide catabolites compared to non-sterile cod, indicating that autolytic enzymes are compartmentalized.
Importance of Handling Practices
- Storing iced fish in boxes over 30 cm deep or allowing stacking can exacerbate autolysis.
- Systems for moving fish must protect delicate tissues from physical damage.
Nucleotide Catabolite Analysis
- Rapid methods exist for determining individual nucleotide catabolites and freshness indices.
Proteolytic Enzymes and Fish Quality
- Autolytic proteolysis in fish leads to tissue softening, most notably in pelagic species like herring, especially during summer feeding, impacting commercial value.
- Autolysis can promote bacterial growth, worsening spoilage and lowering fish quality.
Cathepsins in Fish Autolysis
- Cathepsins, acid proteases stored in lysosomes, become active post-mortem after physical stress, leading to significant tissue breakdown.
- Cathepsin L is a major factor in muscle softening, with its activity correlated to the texture of fish muscle.
Effects of Freezing on Autolysis
- Freezing breaks cell membranes, releasing enzymes like cathepsins, enhancing autolysis and softening.
- Studies show cathepsin L activity is higher in frozen/thawed tissues compared to fresh, influencing the muscle's texture.
Calpains Role in Texture Changes
- Calpains, calcium-activated proteases, significantly contribute to fish muscle autolysis, particularly at physiological pH levels.
- Active at lower temperatures compared to mammalian counterparts, calpains contribute to texture softening during chilled storage.
Collagenase Effects on Fish Texture
- Collagenases weaken connective tissue in fish, leading to gaping in fillets and softening during storage.
- The breakdown of type V collagen correlates with textural degradation of fish tissue.
TMAO and Formaldehyde Production
- TMAO, regulated by bacterial action and intrinsic enzymes, can be converted into dimethylamine and formaldehyde, leading to detrimental toughening of fish muscle.
- Enzymes responsible for this reaction, especially in gadoid fishes, become active upon tissue disruption by freezing.
Prevention Strategies for Autolytic Changes
- Minimizing physical damage and maintaining low storage temperatures (< -30°C) can prevent toughening from autolytic actions.
- Importance of adhering to proper handling practices before freezing to maintain fish quality.
General Summary of Autolytic Changes in Fish
- Both physical disruption and environmental conditions play critical roles in the rate and extent of autolytic changes in fish.
- Key enzymes involved include glycolytic enzymes, autolytic enzymes for nucleotide breakdown, cathepsins, calpains, and collagenases, each with specific impacts on texture and quality.
Effect of Storage Temperature
- Microbial vs. Enzymatic Activity: Temperature between 0-25°C significantly impacts microbial growth more than enzymatic activity; many bacteria, including Shewanella putrefaciens, grow poorly below 10°C, with growth rates drastically reduced at 0°C.
- Extended Shelf Life: Low storage temperatures extend the shelf life of fresh fish products due to reduced microbial spoilage.
- Relative Rate of Spoilage (RRS): RRS is a crucial measure expressed for various seafood stored at different temperatures, showing drastic differences in shelf life at 0°C, 5°C, and 10°C. For example, crab has a shelf life of 10.1 days at 0°C but only 2.6 days at 10°C.
- Spoilage Models: The relationship between temperature and RRS is represented by an S-shaped spoilage curve, confirming earlier research findings and allowing predictions of spoilage based on temperature changes.
- Temperature Influence on Reactions: While the Arrhenius Equation describes temperature effects on chemical reactions, it isn't completely accurate for microbial growth over various temperatures.
- Psychrotrophic Bacteria: Preferred survival temperatures for psychrotrophic bacteria yield a theoretical minimum growth temperature (Tmin), around -10°C for some species, underscoring the effectiveness of optimized storage models.
Superchilling and Partial Freezing
- Superchilling Defined: Storing fish at temperatures from 0°C to -4°C is termed superchilling, which significantly prolongs shelf life compared to regular icing (e.g., shelf life at -3°C can exceed that at 0°C).
- Frigido-system Technology: Developed in the 1960s, this technology maintains sub-zero temperatures in fish holds, reducing fish:ice ratios and enhancing chilling efficacy.
- Negative Effects on Freshness: Some fish may lose quality due to superchilling, with increased drip loss and inferior texture characteristics compared to ice storage, highlighting species variability in response to superchilling.
- Liquid Refrigerated Sea Water (RSW): RSW reduces oxygen exposure and facilitates quicker chilling compared to traditional ice methods, although it may impart a salty taste to some fish species.
Importance of Hygiene During Handling
- Onboard Hygienic Practices: Research indicates that while proper hygiene during fish handling can reduce bacterial contamination, strict measures are less critical compared to rapid chilling methods.
- Bacterial Growth Factors: Initial bacterial levels influence storage life more significantly in the latter stages, with high contamination leading to reduced shelf life post the first week.
- Handling Logistics: Fish storage boxes should permit melt-water drainage to enhance chilling efficiency without significantly increasing contamination risks.
Microbial Control Methods
- Limitations of Traditional Methods: Techniques like irradiation or antibiotics for bacterial control are often rejected due to cost or health concerns.
- Effective Alternatives: CO2 treatment and chlorinated water washing are promising methods for bacterial reduction, improving overall product quality during handling and distribution.
Conclusion and Future Implications
- Superchilling as a Viable Option: While superchilling can improve shelf life significantly, the potential drawbacks for some species necessitate targeted application.
- Technological Advances: Continued development of predictive models and monitoring technologies such as temperature loggers will enhance seafood quality control, ensuring safer consumption practices.### Handling and Storage of Fish
- Chlorine can prolong storage life but creates off-flavors in fish.
- Newly caught fish should be washed in clean seawater to remove visible blood and dirt, with no significant impact on bacterial count or storage life.
Impact of Anaerobic Conditions and Carbon Dioxide (CO2)
- High CO2 concentrations inhibit microbial growth, thereby extending shelf life where spoilage is microbially driven.
- Technologies like vacuum packaging (VP) and modified atmosphere packaging (MAP) are effective, particularly for meats, but provide minimal shelf life extension for fish.
Shelf Life Comparison
- Shelf life (in weeks) at 0.0 - 4.0°C:
- Lean fish:
- Air: 1-2,
- VP: 1-2,
- MAP: 1-3
- Fatty fish:
- Air: 1-2,
- VP: 1-2,
- MAP: 1-3
- Lean fish:
- Meat products show significantly longer shelf lives under similar conditions compared to fish products.
Microbial Spoilage
- Aerobic spoilage in meats is caused primarily by Pseudomonas spp., which are inhibited in anaerobic conditions, shifting spoilage to Gram-positive lactic acid bacteria.
- Fish spoil primarily from Shewanella putrefaciens under aerobic conditions, countered by high CO2 levels in packaged fish.
- Photobacterium phosphoreum, a Gram-negative organism, is identified as the primary spoilage microorganism in vacuum-packaged cod, growing well under anaerobic conditions.
Non-Microbial Spoilage Reactions
- Increased CO2 causes pH decrease (0.2-0.3 units), affecting muscle protein water-holding capacity, leading to higher drip loss in some fish.
- Sensory quality of fish in high CO2 environments may be compromised, particularly at 100% CO2, while up to 60% CO2 shows minimal texture impact on cod.
Refrigerated Seawater (RSW) Systems
- RSW + CO2 improves the shelf life of certain fish products, compared to ice storage.
- CO2 can prolong the shelf life of pink shrimp significantly, but may adversely affect color and texture in other species like mackerel.
Factors Affecting Quality and Storage Life
- Evisceration generally enhances quality and shelf life, particularly in lean species like cod, where ungutted fish show rapid quality degradation.
- Gutting increases exposure to air, raising oxidation risks, leading to discoloration.
Species-Specific Insights
- Fatty fish like herring and sardines are often stored ungutted due to challenges with discoloration and rancidity.
- Quality of perishable fish species is affected by species, fishing grounds, fishing methods, and seasonal factors.
Intrinsic Factors of Spoilage
- Spoilage is slower in larger fish, flat fish tend to keep better, and lean fish have longer storage capabilities than fatty species.
- Factors such as rough handling lead to increased spoilage rates due to physical damage increasing bacterial access.
Bacterial Growth and Spoilage Rate
- Post-mortem pH and fat content directly influence spoilage rates; higher pH and fat content generally lead to faster spoilage.
- Bacterial growth rates differ among species, impacting overall shelf life.
Environmental and Temperature Influences
- Cold-water species generally exhibit shorter iced shelf lives than tropical species, which have been reported to outperform in storage longevity.
- Historical studies have shown some tropical fish maintain freshness in ice for 20-30 days, indicating a significant difference in spoilage dynamics between warm and cold-water species.### Fish Shelf Life Comparison
- Fish from warm waters generally have longer shelf lives compared to those from temperate waters.
- Freshwater fish species exhibit longer shelf lives than marine species.
- Tropical marine fish can last 12-35 days when stored in ice, whereas temperate marine fish last 2-21 days.
- Temperate freshwater fish shelf life ranges from 9 to 20 days.
Factors Affecting Fish Spoilage
- Prolonged shelf life in tropical fish may be related to lower levels of Trimethylamine (TMA) and Total Volatile Nitrogen (TVN) during storage.
- Pseudomonas spp. are often responsible for spoilage in tropical fish, differing from Shewanella spp. which produce TMA and sulfides.
- The absence of TMA and TVN in some tropical fish suggests spoilage mechanisms that might not involve typical bacteria.
- Tropical fish exhibit a lag phase of 1-2 weeks before bacterial growth resumes when stored in ice.
Bacterial Flora Influences
- Gram-negative bacteria such as Pseudomonas and Acinetobacter are prevalent in tropical fish, potentially influencing spoilage rates.
- Studies show high percentages (40-90%) of tropical fish bacteria can grow at chill temperatures (7°C).
- Tropical fish tend to have slower spoilage rates compared to temperate fish, supporting the adaptation hypothesis.
Physiological Differences
- pH levels of tropical fish measured between 6-7, lower than some temperate species, may contribute to longer shelf life.
- The thick skin of tropical fish might also play a role in preservation, though further research on skin properties is needed.
Off-Flavours in Fish
- Off-flavours in fish can arise from diet, leading to taints such as "mineral oil" from planktonic molluscs.
- Bitter tastes in herring can be due to larvae from Mytilus spp., while muddy-earthy taints in freshwater fish stem from geosmin and 2-methylisoborneol.
- Iodine-like flavours may indicate the presence of volatile bromophenolic compounds derived from marine organisms.
- Environmental factors, such as oil spills, can cause oil taint due to soluble hydrocarbon compounds that accumulate in fish flesh.
Storage and Handling Practices
- Proper handling, such as rapid chilling of ungutted fish, is crucial for maintaining quality.
- The type of bacterial flora and environmental conditions before and after catch impact fish longevity and quality.
Effect of Storage Temperature
- Microbial vs. Enzymatic Activity: Temperature between 0-25°C significantly impacts microbial growth more than enzymatic activity; many bacteria, including Shewanella putrefaciens, grow poorly below 10°C, with growth rates drastically reduced at 0°C.
- Extended Shelf Life: Low storage temperatures extend the shelf life of fresh fish products due to reduced microbial spoilage.
- Relative Rate of Spoilage (RRS): RRS is a crucial measure expressed for various seafood stored at different temperatures, showing drastic differences in shelf life at 0°C, 5°C, and 10°C. For example, crab has a shelf life of 10.1 days at 0°C but only 2.6 days at 10°C.
- Spoilage Models: The relationship between temperature and RRS is represented by an S-shaped spoilage curve, confirming earlier research findings and allowing predictions of spoilage based on temperature changes.
- Temperature Influence on Reactions: While the Arrhenius Equation describes temperature effects on chemical reactions, it isn't completely accurate for microbial growth over various temperatures.
- Psychrotrophic Bacteria: Preferred survival temperatures for psychrotrophic bacteria yield a theoretical minimum growth temperature (Tmin), around -10°C for some species, underscoring the effectiveness of optimized storage models.
Superchilling and Partial Freezing
- Superchilling Defined: Storing fish at temperatures from 0°C to -4°C is termed superchilling, which significantly prolongs shelf life compared to regular icing (e.g., shelf life at -3°C can exceed that at 0°C).
- Frigido-system Technology: Developed in the 1960s, this technology maintains sub-zero temperatures in fish holds, reducing fish:ice ratios and enhancing chilling efficacy.
- Negative Effects on Freshness: Some fish may lose quality due to superchilling, with increased drip loss and inferior texture characteristics compared to ice storage, highlighting species variability in response to superchilling.
- Liquid Refrigerated Sea Water (RSW): RSW reduces oxygen exposure and facilitates quicker chilling compared to traditional ice methods, although it may impart a salty taste to some fish species.
Importance of Hygiene During Handling
- Onboard Hygienic Practices: Research indicates that while proper hygiene during fish handling can reduce bacterial contamination, strict measures are less critical compared to rapid chilling methods.
- Bacterial Growth Factors: Initial bacterial levels influence storage life more significantly in the latter stages, with high contamination leading to reduced shelf life post the first week.
- Handling Logistics: Fish storage boxes should permit melt-water drainage to enhance chilling efficiency without significantly increasing contamination risks.
Microbial Control Methods
- Limitations of Traditional Methods: Techniques like irradiation or antibiotics for bacterial control are often rejected due to cost or health concerns.
- Effective Alternatives: CO2 treatment and chlorinated water washing are promising methods for bacterial reduction, improving overall product quality during handling and distribution.
Conclusion and Future Implications
- Superchilling as a Viable Option: While superchilling can improve shelf life significantly, the potential drawbacks for some species necessitate targeted application.
- Technological Advances: Continued development of predictive models and monitoring technologies such as temperature loggers will enhance seafood quality control, ensuring safer consumption practices.### Handling and Storage of Fish
- Chlorine can prolong storage life but creates off-flavors in fish.
- Newly caught fish should be washed in clean seawater to remove visible blood and dirt, with no significant impact on bacterial count or storage life.
Impact of Anaerobic Conditions and Carbon Dioxide (CO2)
- High CO2 concentrations inhibit microbial growth, thereby extending shelf life where spoilage is microbially driven.
- Technologies like vacuum packaging (VP) and modified atmosphere packaging (MAP) are effective, particularly for meats, but provide minimal shelf life extension for fish.
Shelf Life Comparison
- Shelf life (in weeks) at 0.0 - 4.0°C:
- Lean fish:
- Air: 1-2,
- VP: 1-2,
- MAP: 1-3
- Fatty fish:
- Air: 1-2,
- VP: 1-2,
- MAP: 1-3
- Lean fish:
- Meat products show significantly longer shelf lives under similar conditions compared to fish products.
Microbial Spoilage
- Aerobic spoilage in meats is caused primarily by Pseudomonas spp., which are inhibited in anaerobic conditions, shifting spoilage to Gram-positive lactic acid bacteria.
- Fish spoil primarily from Shewanella putrefaciens under aerobic conditions, countered by high CO2 levels in packaged fish.
- Photobacterium phosphoreum, a Gram-negative organism, is identified as the primary spoilage microorganism in vacuum-packaged cod, growing well under anaerobic conditions.
Non-Microbial Spoilage Reactions
- Increased CO2 causes pH decrease (0.2-0.3 units), affecting muscle protein water-holding capacity, leading to higher drip loss in some fish.
- Sensory quality of fish in high CO2 environments may be compromised, particularly at 100% CO2, while up to 60% CO2 shows minimal texture impact on cod.
Refrigerated Seawater (RSW) Systems
- RSW + CO2 improves the shelf life of certain fish products, compared to ice storage.
- CO2 can prolong the shelf life of pink shrimp significantly, but may adversely affect color and texture in other species like mackerel.
Factors Affecting Quality and Storage Life
- Evisceration generally enhances quality and shelf life, particularly in lean species like cod, where ungutted fish show rapid quality degradation.
- Gutting increases exposure to air, raising oxidation risks, leading to discoloration.
Species-Specific Insights
- Fatty fish like herring and sardines are often stored ungutted due to challenges with discoloration and rancidity.
- Quality of perishable fish species is affected by species, fishing grounds, fishing methods, and seasonal factors.
Intrinsic Factors of Spoilage
- Spoilage is slower in larger fish, flat fish tend to keep better, and lean fish have longer storage capabilities than fatty species.
- Factors such as rough handling lead to increased spoilage rates due to physical damage increasing bacterial access.
Bacterial Growth and Spoilage Rate
- Post-mortem pH and fat content directly influence spoilage rates; higher pH and fat content generally lead to faster spoilage.
- Bacterial growth rates differ among species, impacting overall shelf life.
Environmental and Temperature Influences
- Cold-water species generally exhibit shorter iced shelf lives than tropical species, which have been reported to outperform in storage longevity.
- Historical studies have shown some tropical fish maintain freshness in ice for 20-30 days, indicating a significant difference in spoilage dynamics between warm and cold-water species.### Fish Shelf Life Comparison
- Fish from warm waters generally have longer shelf lives compared to those from temperate waters.
- Freshwater fish species exhibit longer shelf lives than marine species.
- Tropical marine fish can last 12-35 days when stored in ice, whereas temperate marine fish last 2-21 days.
- Temperate freshwater fish shelf life ranges from 9 to 20 days.
Factors Affecting Fish Spoilage
- Prolonged shelf life in tropical fish may be related to lower levels of Trimethylamine (TMA) and Total Volatile Nitrogen (TVN) during storage.
- Pseudomonas spp. are often responsible for spoilage in tropical fish, differing from Shewanella spp. which produce TMA and sulfides.
- The absence of TMA and TVN in some tropical fish suggests spoilage mechanisms that might not involve typical bacteria.
- Tropical fish exhibit a lag phase of 1-2 weeks before bacterial growth resumes when stored in ice.
Bacterial Flora Influences
- Gram-negative bacteria such as Pseudomonas and Acinetobacter are prevalent in tropical fish, potentially influencing spoilage rates.
- Studies show high percentages (40-90%) of tropical fish bacteria can grow at chill temperatures (7°C).
- Tropical fish tend to have slower spoilage rates compared to temperate fish, supporting the adaptation hypothesis.
Physiological Differences
- pH levels of tropical fish measured between 6-7, lower than some temperate species, may contribute to longer shelf life.
- The thick skin of tropical fish might also play a role in preservation, though further research on skin properties is needed.
Off-Flavours in Fish
- Off-flavours in fish can arise from diet, leading to taints such as "mineral oil" from planktonic molluscs.
- Bitter tastes in herring can be due to larvae from Mytilus spp., while muddy-earthy taints in freshwater fish stem from geosmin and 2-methylisoborneol.
- Iodine-like flavours may indicate the presence of volatile bromophenolic compounds derived from marine organisms.
- Environmental factors, such as oil spills, can cause oil taint due to soluble hydrocarbon compounds that accumulate in fish flesh.
Storage and Handling Practices
- Proper handling, such as rapid chilling of ungutted fish, is crucial for maintaining quality.
- The type of bacterial flora and environmental conditions before and after catch impact fish longevity and quality.
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Explore the fascinating world of fish, from their anatomy and physiology to their classification and taxonomy. This quiz covers various groups, habitats, and characteristics that define fish as aquatic vertebrates. Test your knowledge on the diversity of over 20,000 species and their evolutionary relationships.