Fish and Aquatic resources in Human Nutrition

• Fish and aquatic resources play a vital role in human nutrition

Lecture Objectives

• The role of fish and aquatic resources in nutrition needs to be understood
• It is also important to recognize the unique nutritional benefits of fish
• Critical to discuss the importance of including fish in a balanced diet

Nutritive Value of Fish

• Fish provide a very good balance of nutrients
• Healthy due to fish oils, specifically PUFA or omega-3
• Fish offers a low-calorie, low-fat nutritional edge
• Fish is a good source of vitamins A and B complex
• Fish contains minerals such as iodine, fluoride, selenium, and zinc

Other Aquatic Resources

• Oysters and mussels are high in iron, surpassing levels in red meats
• Seaweed and algae contain iodine, fiber, and omega-3
• Shellfish are high in zinc, iron, and vitamin B12
• Fish oil provides concentrated omega-3, beneficial for those who do not consume fish

Fish Structure and Muscles

• Fish are divided into three classes
• Cephalaspidomorphi includes jawless fish like lampreys and slime eels
• Chondrichthyes encompasses cartilaginous fish (elasmobranchs) such as sharks and rays
• Osteichthyes includes lungfish and bony fishes (teleosts)
• The edible part of fish constitutes about 60% of its total weight
• Fish muscle comprises myocommata, myotomes, and fat
• Myocommata is the thin connective tissue membrane that divides fish muscle into blocks called "myotomes"
• Myotomes consist of muscular tissue
• The length of fibers and the thickness of the myocommata increase with age
• Cooked myocommata gelatinize, causing the myotomes to appear in blocks
• Raw fish meat reveals conspicuous myotomes when shredded

Myocommata

• Myocommata primarily contains collagen
• Collagen breaks down in hot water
• This facilitates flaking of myotome blocks between myocommata sheets during cooking
• Bony fish contain 3% collagen
• Cartilaginous fish contain 16% collagen
• Collagen is also present in the perimysium and endomysium of fish
• Perimysium envelops the muscle bundle
• Endomysium encloses the muscle cell or fiber
• In mammals, connective tissue protein makes up 17% of the total protein

Types of Fish Muscle

• White muscle forms the bulk of the edible portion, it is non-pigmented and constitutes about 90% of the muscle
• 90% white muscle (light or no pigment) sprinting muscle for abrupt, fast movements
• Red or dark muscle fans out on either side of the lateral line; makes up about 10% of the muscle in tropical white fish
• Color is due to the pigment myoglobin
• Contains high levels of hemoglobin, histidine, lipids, and enzymes
• Red/dark muscle is prone to oxidation
• 10% red (dark) cruising muscle contains myoglobin pigment for slow continuous motion
• The composition of these muscle types differs, with dark muscle having more lipids, hemoglobin, glycogen, and vitamins
• Edible portions are dominated by darker pigmented muscle blocks along the lateral line
• Dark muscle is almost always fatty, makes it is more susceptible to spoilage than white fish
• Dark muscle is perceived as more tasteful

Fish Composition

• Understanding the composition of fish is important for food processors, nutritionists, and consumers
• Composition of fish varies by species and individual based on age, sex, environment, and season
• Key components of fish include protein, fat (lipids), vitamins, minerals, and minor components
• Fish protein is composed of amino acids
• Fish provides 16-22% high-quality essential amino acids
• These amino acids are needed for building and repairing muscles, internal organs, skin, and hair
• Fish provides all 9 essential amino acids: lysine, valine, tryptophan, histidine, threonine, leucine, methionine, isoleucine, and phenylalanine
• Lysine and methionine are essential amino acids often lacking in cereal and root crop diets
• Protein deficiency lowers the body's resistance to illness and hinders growth, this is particularly harmful to children

Fish Fat (Lipids)

• Fat content ranges from 0.2-25% in fish
• Tropical species rarely exceed 5% fat
• 80% of flesh is water and fat
• Fish lipids contain long-chain fatty acids (14-22 carbon atoms) that are highly unsaturated
• Has carbon atoms with 5 to 6 double bonds
• Fish fat is rich in high-grade PUFAs (omega-3)
• 2 of the 7 omega-3 fatty acids (EPA and DHA) are not found in beef, pork, or vegetables
• EPA (eicosapentaenoic acid)
• DHA (docosahexaenoic acid) is important for brain growth and development
• Omega-3 prevents heart disease by suppressing blood clot formation
• Fish oils decrease blood circulatory diseases
• Fish oils decrease serum total cholesterol levels
• Fish oils increase HDLP (high density lipoprotein) cholesterol
• Omega-3 fatty acids from tuna processing waste can be converted into capsules
• They oxidize easily, deteriorating quality and become darker and rancid
• Unfavorable conditions can change the color from light yellow to red-brown
• Fatty fish has more than 5% lipid
• Medium fatty fish has 2-5% lipid
• Lean fish has less than 2% lipid

Vitamins and Minerals

• Vitamin content varies across species
• Red meat is rich in vitamins A, B1, B2, B12, and D3
• Fish skin contains more B1 and B2 than flesh
• Fish liver is rich in vitamins A, D3, and B3 (Niacin)
• Molluscs and crustaceans are important sources of B complex vitamins B6 and B3
• Vitamin A prevents night blindness, promotes growth, and reduces susceptibility to infections
• Vitamin B group prevents mental depression, convulsions, irritability, anemia, nerve damage, skin rashes, tissue degeneration, and weight loss
• Vitamin D3 is found in fish, assists with calcium metabolism
• Minerals are in the form of organic salts such as potassium, sodium, calcium, magnesium, phosphorus, sulfur, and chlorine
• Minerals assist in depressing the freezing point of tissue fluids
• Iodine is found in fish, seaweeds, mollusks, and crustaceans, it is essential for thyroid function
• Fluorides in fish protect against tooth cavities
• Selenium prevents heart disease and possibly cancer
• Fish are low in sodium and good food choice for health-conscious people

Other Components

• Water content in fish is generally high, from 60-90%, this favors microorganism viability and causes spoilage
• Taurine (sulphonic AA) decreases total cholesterol in blood and is important for brain fetal development
• Carbohydrates are not a key component of fish, however glycogen is of concern due to its role in rigor formation
• Glycogen, often called "animal starch," is a reserve carbohydrate
• Glycogen is present in relatively small amounts, about 1.5% in the liver and 0.5-1.0% in muscle
• Water: 60-90%
• Protein: 10-25%
• Fat: 1-24%
• Minerals (Ca, P, Fe, Mg, Cu): 0.1 - 5%
• Vitamins (A, D, thiamin, B12, riboflavin, nicotinic acid): Trace
• Bykov (1974) Parts and Main Components Utilization of Fish chart

Factors Affecting Variance in Fish Composition

• Species: Each species has different levels of protein, fat, and moisture
• Diet: The food consumed by fish influences the lipid and nutrient content
• Environment: Fish from colder waters have higher fat content
• Seasonal variation: Place of catch is a large variant
• the fresher the water the fresher the fish
• Sexual maturation: Spawning cycles and feeding habits impact fish composition
• Processing methods: Handling, freezing, and cooking can alter nutrient content

Fish in a Balanced Diet

• Fish offers an affordable source of high-quality nutrition
• Fishing supports livelihoods in coastal areas
• Fish is integral to cultural diets worldwide
• The WHO recommends 2 servings of fish per week

Challenges in Fish Nutrition

• Sustainability: Overfishing and environmental degradation
• Promoting sustainable fishing and aquaculture is important to protect against overfishing
• Spoilage: High moisture and fat content require proper handling to prevent spoilage