Fish Anatomy PDF

Fish Anatomy  Objectives of this course 1. Know classification of fishes and common species found in Egypt. 2. List and describe external and internal anatomical features of a typical fish. 3. Compare between bony and cartilaginous fish. 4. Recognize anatomical variations of...

Fish Anatomy  Objectives of this course 1. Know classification of fishes and common species found in Egypt. 2. List and describe external and internal anatomical features of a typical fish. 3. Compare between bony and cartilaginous fish. 4. Recognize anatomical variations of fish to accommodate with living in water. - Ichthyology (Icthy = fish and Ology = science) is the science which studies fish. - Fishes are cold-blood aquatic vertebrates ( their blood Temperature ranges from the freezing point upward, in accordance with the temperature of the surrounding medium; poikilothermic). - Fishes breathe by gills and move by fins. - - Fish anatomy is required to understand the normal structure of different body structures and organs of fish which is necessary to know the physiology of fish and to expect fish abnormalities and diseases.  Classification of Fishes A) According to nature of skeleton: 1- Bony fishes 2- Cartilaginous fishes (Teleosts) (Chondrosts) Have bony skeleton Have cartilaginous skeleton Higher order fishes which include the Lower order fishes majority of known fishes Examples: Tilapia nilotica (Nile bolti), Shark , Rays, Skates Catfish (Calarias), Mugil cephalus (bouri), Carp, Bass (karos) , Salmon, Eel, Trout. NB: Another type called jawless fish has no jaws such as Hagfish: eel-shaped, slime-producing marine fish (called slime eels). They have a skull but no vertebral column Lamprey: it is also called, lamprey eels Hagfish Lamprey B) According to the nature of water they live in: 1- Fresh water fish 2- Marine (salt) water fish 3- Brackish water fishes Tilapia, Carp, Catfish Shark, Seabass, Seabream Mugil, Salmon, Eel Brackish water or briny water is water that has more salinity than fresh water, but not as much as sea water. It may result from mixing of seawater with fresh water, as in estuaries ‫مصبات االنهار‬ C) According to fish migration: 1- Non-migratory fishes 2- Migratory (for spawning) fishes From sea to fresh water From fresh to sea water Tilapia Salmon Eel D) According to nature of food: 1- Herbivorous fishes 2- Carnivorous fishes 3- Omnivorous fishes Eat algae and vegetables Eat fries and meat Eat both algae and fries Tilapia Shark River carpsucker  External features of fish The body of fish consists of three regions which are: The head (the region from mouth to the caudal border of the operculum), The trunk (the largest region which extends from the caudal border of the operculum till the beginning of the anal fin). The tail (the region from the anal fin till the end of the tail fin). I) The head region: Subdivided into the following regions: 1- Snout: The region from eye to lips. 2- Occiput: The region from eyes till the beginning of the operculum (gill cover). 3- Nuchal region: The region from the occiput to the beginning of dorsal fin. 4- Isthmus: The region between and below the two gill covers. The head region contains the following structures and organs: 1- Mouth: It will be described later (digestive system). 2- Nostrils (nares): - They are the external openings of the nose which are located on the dorsal surface of head (in snout region). - They lead to nasal sac which is closed except in lung fishes. - Function: a- Enable fish to respond to chemical stimuli. b- Help in respiration (in lung fish only). 3- Eye: - Present in a bony cavity called myodome. - In bony fishes no eyelids, while in cartilaginous fish such as sharks there is one medial eyelid. - Unlike other vertebrates, the eye lens of fish is round. - Function: It is the organ of vision which is very sensitive to any little amount of light. 4- Ear: - There is only inner ear which has a sensitive structure called otolith (no external or middle ear). - The ear is covered externally by skin and scales to prevent entrance of water current to the interior of the fish. - Carps and catfishes have middle ear-like ossicles (Weberian ossicles) to transmit vibrations of the swim bladder, which functions as a tympanic membrane (ear drum), to the inner ear. - Function: Hearing and balance. 5- Barbs (Barbels): - They are sensory appendages which have cartilaginous core and covered with skin. - There are maxillary and mandibular barbels near the mouth. - They present in some species such as catfish (long barbels) and carp (short barbels). - Function: Sensation (search for food) as they have taste buds and free nerve. 6- Gill cover (Operculum): - It is a bony plate covers the gills in bony fishes. - It leaves a gill opening caudally and ventrally. - Function: It protects and supports gill filaments. 7- Branchiostegal membrane: - It connects the two opercula ventrally at the isthmus region. - It is supported by bony rays called branchiostegal rays - Function: It covers the gill opening ventrally. II) Trunk Region: It is subdivided into: 1- Breast region: A triangular region caudal to the isthmus till the beginning of pelvic fins. 2- Abdomen (belly): - It extends from the pelvic fin till the beginning of anal fin. - Free from scales (ventrally). - It contains two openings: anus (cranially) and vent (urogenital opening or genital papilla) NB: The belly of some female fishes contains three openings from cranial to caudal (anus, genital tract opening and urinary opening). III) Tail region: It is divided into: 1- Tail (caudal) peduncle: - A fleshy part contains no internal organs. - Extends from the anal fin to the beginning of the tail fin. - The site of blood sampling. 2- Tail fin: It will be mentioned later with fins.  Lateral line system Definition: It is a system of sense organs composed of hair-like sensory structural units called neuromasts which are either irregularly distributed in the head (forming lateral sensory organ) or regularly arranged in form of lateral line on the dorsolateral surface of the trunk and tail. Lateral line system = lateral sensory organ (in head) + lateral line (in trunk and tail) The lateral line opens to the water through a series of pores (creating a line along the side of the fish from behind the head till the tail).  The neuromast is composed of receptive hair cells covered with jelly-like flexible structure called cupula. The receptive hair cells are modified epithelial cells have bundles of 40-50 microvilli (hairs) which act as mechanoreceptor Types: 1. Complete (in rapid swimmers and river fishes) 2. Incomplete (in slow swimmers fishes) 3. Single (as in Tilapia) 4. Double (as in some fishes) NB: The lateral line is absent in some fishes such as Herrings. Function: The organ of long distance touch sensation as it carries mechanoreceptors. Environmental information: It enables the fish to feel any changes in the water due to any movement (pressure, current, sound) around the fish.  The Locomotor system of the fish I) Passive locomotor system: Consists of skeleton of the fish which is divided into: 1- Axial skeleton (a- Skull, b- Vertebral column, c- Pectoral and Pelvic girdle) 2- Appendicular skeleton (fins) 3- Dermal skeleton (scales) II) Active locomotor system: Consists of skeletal muscles which is divided into: 1- Red muscles 2- White muscles  1- Axial skeleton a- Skull: It is formed of small bones joined together with cartilaginous and fibrocartilaginous joints. b- Vertebral column: i- In cartilaginous fishes: Vertebral column is replaced by a cartilaginous rod (notochord) which is either non segmented (sturgeon ‫ )سمكة الحفش‬or segmented (sharks). ii- In bony fishes: The vertebral column is segmented into vertebrae. Each vertebra is formed of body (centrum), arches and processes. - The vertebrae of the tail region called hemal vertebrae while that of the trunk region are called prehemal vertebrae. The latter articulate ventrally with the ribs. - The dorsal (neural) arches meet together and form neural canal through which the spinal cord passes. - The ventral (hemal) arches in tail region meet together and form hemal canal through which the caudal artery and vein (site of blood sampling) pass. c- Pectoral girdle - It is composed of scapula and basalia which are attached to rays of pectoral fins and to the opercula and branchiostegal rays. d- Pelvic girdle - It is formed of two bones which fuse and form a V shape single bone that attached to the rays of pelvic fin and the branchiostegal rays. 2- Appendicular skeleton (Fins) Structure: - They are formed of skin folds supported by special structures called fin rays or by loose connective tissue. - The fin rays may be soft (fleshy) rays or hard rays (bony spines) or both. A- Unpaired: Present on the median plane and includes: 1- Dorsal fin 2- Tail (caudal) fin 3- Anal fin Position: On dorsal surface of fish Directly attached to the axial skeleton at Presents caudal to the tail region. vent Structure/Type/Shape - Bony and soft rays - Composed of bony - Composed of bony and soft rays. The - The swimming habits may be deduced and soft rays - It is bony rays are supported by fin ray bearers from the caudal fin: generally short, but which connect them with neural spines of 1- fish with lunate (crescent or some species have vertebrae. The bearers and neural spines semilunar) caudal fin and a narrow tail elongated anal fins form a median septum between trunk peduncle are the speediest fishes stretching from the musculature. 2- fish with forked tail are high speed fish anus to the caudal fins - May be formed of one part (tilapia) or but less than (1) divided into two (mugil, bass and shark) or 3- fish with truncate or round or three separate parts. marginated caudal fins are strong Adipose fin: swimmers but somewhat slower than (1 - present in some fishes (as salmon and and 2). catfish) as an extra fin between dorsal and 4- Fishes with small caudal fin or their tail fins caudal fin continues with the dorsal and the - contains no fat (the name adipose is anal fins are weak swimmers or wriggling misleading) but instead it contains loose in bottom. connective tissue The functions: 1- The main fin for forward movement. 1- Balance 1- Stabilization (balance) 2- Control direction 2- Help in quick 2- Quick changes in direction 3- Determines the speed of swimming changes in direction 3- Modified into sucking pad as in sharksuckers (to fix that fish to shark) 4- Modified into illicium to attract the prey as in angler fish Angler fish illicium Remora (sucker fish) Adipose fin B- Paired (double) fins: Present lateral to median plane and includes: 1- Pectoral fin 2-Pelvic fin Position: Fixed position in shoulder Present below the pectoral fin (pectoral) girdle with great variation in position (may be jugular, thoracic or abdominal) Structure: Soft rays only Bony rays and a few soft rays Functions 1- Help pectoral fins in 1- Steering and changing direction of fish stabilization and braking 3- Stabilization (balance) 2- Modified to form male 4- Act as brakes as fish may rest on them copulatory organs as claspers in 5- Bear taste buds and touch receptors sharks and gonopods in males 6- Catfish has spine like structure at fin of some Teleosts. the cranial edge, used as weapons for defence.  3-Dermal skeleton (Scales): The Scales are bony plates arise from the dermal layer of the skin and projected externally in a caudal and overlapping direction. Types of the scales: 1- Small (placoid or 2- Large Scales dermal teeth) Scales - present in cartilaginous - present in bony fish (see below). fishes as sharks - its size is ranged from few mm to size of man’s hand - It measures 0.2 – 3 mm - Its size increase with the growth of the fish. - Its size is always fixed. - They are divided into the following: - Torpedo )‫ (قذيفه‬shape with A. rhomboid scales B. Round Scales pointed ends (Ganoid Scales) - resembles the tooth in its i. Cycloid ii. Ctenoid structure as it has crown, - rhomboid - oval to round - round neck, base and pulp cavity; - Contains a peg - smooth borders - teeth like projections it also contains dentine and shaped process and caudally and caudally and enamel socket, each peg is indentations cranially indentations cranially - give rise to teeth of sharks fitted in socket of - as in salmon - as in perch overlap scale. - Both cycloid and ctenoid present in solea and - present in sturgeon Tilapia nilotica. and gar - give rise to dermal bones of the head region and fin rays Function of scales: 1- Protection: from injury and external parasites. 2- The white and dark scale rings are used for the determination of the age, the nutritional value of the water and the environmental changes all over the year. For example: In summer, the nutrition is sufficient and the weather is fine so the scale rings become broader. In winter, the nutrition is insufficient and the weather is very cold so the scale rings become narrower and darker as they become closely adherent to each other. One season = white ring + dark ring NB:- The hatched fries have no scales which develop later. - Scales are absent in some fishes such as catfish.  The skin Structure: The skin consists of the following layers from out to inward: 1-Cuticle: It contains mucus secretion called slime 2-Epidermis - Contains mucus glands and goblet cells which secrete the slime - It contains pigmented cells which give the fish its colour - It contains club (alarm) cells for sensation 3- Basement membrane 4- Dermis: It forms pockets for the scales 5-Hypodermis: It contains connective tissues and nerves and blood vessels Function 1- The primary barrier against the environment. 2- The slime prevents penetration of microorganisms, decreases loss of body fluids and can be used as a method of escaping from enemy. 3- Carries scales. 4- Makes fish shiny (reflect the light efficiently).  II) Active locomotor system (Fish musculature) Fish musculature is divided into: A) Somatic muscles which divided into: (1) axial muscles (Muscles of trunk and tail) and (2) extremity muscles (Muscles of pectoral and pelvic fins). B) Visceral musculature which divided into: (1) gills muscles (striated) and (2) muscles of the digestive tract (smooth). Types of muscle fibers: 1- Red muscle fibers 2- White muscle fibers narrow fibers but contains fat broad fibers but no fat contains myoglobin so appear red no myoglobin so appear white aerobic metabolism because it receives anaerobic metabolism because it sustained oxygen from its rich blood receives low O2 from its poor blood supply supply contracts weakly but continuously so the contracts rapidly, strongly and for short fish used it for slow movement during time so the fish used it for rapid normal swimming movements during attacking form the superficial, fins and gill muscles form the bulk of trunk and tail muscles Body Shape and Form The Digestive system of fish 1-The mouth: The reproductive system  The male copulatory organs They either perform the copulatory process during internal fertilization or adjust the insemination in the external fertilization. They include the following:  A- The heart - situated inside the pericardium ventral to gills and separated from the liver by septum transversus (diaphragm anlagen). - has two true chambers (atrium and ventricle which have cardiac muscles) and two false chambers (sinus venosus and bulbus arteriosus without cardiac muscles).  1- Sinus venosus 2- The atrium 3- The ventricle 4- The bulbus arteriosus Position caudal to atrium cranial to sinus ventral to atrium and cranial to ventricle venosus and dorsal caudal to bulbus ventricle arteriosus Size So small with thin Larger wall than (1) Larger and thicker Larger, thicker than wall wall than (2) (1), but less than (2) Cardiac No cardiac muscles Contains cardiac Contains outer No cardiac muscles muscles (so no pulsation) muscles with few compact layer of but there are elastic trabeculae cardiac muscle and an tissue and smooth inner spongy layer of muscle trabeculae Function Receives Forces blood through the main force for 1- Conducts venous blood from duct of valves into ventricle circulatory flow into blood to gills Cuvier and hepatic the bulbus arteriosus 2- Control blood V. and conducts it pressure to the atrium  B- Blood vessels (Blood cycle or circulation) 1- Arteries A- Ventral Aorta - It carries nonoxygenated blood and extends cranially from bulbus arteriosus toward gills ventral surface. It gives Four pairs of afferent branchial arteries enter the gill arches to give rise to two afferent arterioles which enter the primary gill lamellae and give afferent capillaries to the secondary lamellae. - After exchange of gases takes place in secondary gill lamellae, the oxygenated blood collected by efferent capillaries which leave the secondary lamellae as efferent arterioles (NB: there are two efferent arterioles; the cranial one is called the pretrematic arteriole and the caudal one called posttrematic arteriole) which leave the gill arch as four pairs of efferent branchial arteries which terminate in the dorsal aorta. B- Dorsal Aorta - It connects with efferent branchial arteries so it carries oxygenated blood to all body. - Anteriorly, the dorsal aorta is paired and extends to the head as the carotid arteries. - Posteriorly, the dorsal aorta is unpaired through the trunk region and gives branches to viscera (celiac, mesenteric and renal arteries) and trunk musculatures (segmental arteries). - More posteriorlay, it continues into the tail as the caudal artery, running through the hemal arches of the vertebrae. 2- Veins a. Caudal vein runs through the hemal arches ventral to the caudal artery NB: Blood sample in fish is taken from caudal vein and artery. b. Renal portal system; i. renal portal vein collects blood from tail region and enter the kidney. ii. renal vein collect blood from kidney and open post-cardinal vein. c. Post-cardinal (posterior cardiac) veins receive blood from kidneys, gonads and musculature as they run forward to join common cardinal veins (ducts of Cuvier). d. Pre-cardinal, subclavian and jugular veins enter ducts of Cuvier. e. Ducts of Cuvier; collect blood from (c), (d) and then terminates in the sinus venosus of the heart. f. Hepatic portal system; i. hepatic portal vein collects blood from alimentary canal and enter liver ii. hepatic vein collect blood from liver (portal circulation) and open in sinus venosus.  The respiratory system - In all fishes (except lung fish), respiration occurs by gills which replace the lung. Animals Most Fishes Internal lung External gills Bi-direction flow of air (O2 in and CO2 Uni-direction flow of water out) The gills (branchs) - Healthy gills are bright red and do not stick together. - There are four pairs of gills (four in each side of pharynx) which covered by operculum. - They are located between buccal cavity and opercular cavity. - The gills compose of gill rakers, gill arch, gill lamellae and gill musculatures. 1- Gill rakers - Cartilaginous or bony tubercles attached to gill arch cranial part and face buccal cavity. - Their number and arrangement varied according to size of food particles. For example: a. Fishes eat large size particles have rakers with large size but few and apart from each other. b. Fishes eat small size particles have rakers with small size but numerous and close to each other - Function: Filter feeding, the rakers act as a sieve as they prevent escaping of food particles from the pharynx to gill lamellae so save fish from suffocation. 2- Gill arches - Cartilaginous curved plates (which called gill bar) which its cranial concave border attaches to gill rakers and its caudal convex border to gill filaments. - There are four gill arches on each side, each gill arch attaches to one holobranch (two hemibranchs) of the filaments. - Within each gill arch, there are two arteries; the afferent branchial artery which comes from the ventral aorta (carries non-oxygenated blood) and the efferent branchial artery (carries oxygenated blood, it has pre and post-trematic branches) which connects with the dorsal aorta. - It gives a cartilaginous support called gill rays to support the gill filaments. NB: The gill arch = gill bar + gill rays + afferent and efferent branchial artery 3-The gill lamellae (filaments) - The gills filaments comprise two sets of four holobranchs forming the sides of the pharynx (4 in each side of the pharynx). - Each holobranch consists of two hemibranchs (which are cranial (anterior) and caudal (posterior) hemibranchs) projecting from the caudal convex border of the gill arch and diverge and touch those of adjacent holobranch. NB: On each side of the pharynx, there are 4 gill arches, 4 holobranchs and 8 hemibranchs - Each hemibranch consists of a row of long thin filaments, the primary lamellae which projects as teeth of a comb. - The primary lamellae carry the secondary lamellae which project from the dorsal and ventral part of the primary lamellae as regular semilunar fold. - The secondary gill lamellae contain within its core numerous wide thin walled capillaries which designated as the gill sinusoids (blood spaces) separated from each other by pillar cells which originate from the epithelial cells of the filaments - At the base of the secondary lamellae there are special cells called the chloride cells which are responsible for the mineral balance in the body. - The secondary filaments are the sites for gaseous exchange. 4- Gill musculature: a. Adductor muscles; between each 2 hemibranchs b. Abductor muscles; between hemibranchs base and gill arch Accessory arborescent (labyrinth) organs - It is richly vascularised, thin wall organ which presents in the caudal extension of the opercular cavity of catfish. - They arise as out-pocketing from the dorsal part of 2nd and 4th gill arches. - It acts as a temporary lung which helps catfish to live for comparatively long time outside the water.  Mechanism of respiration in fishes (Counter current flow mechanism) In this mechanism, water current moves on the gill lamellae in opposite direction to the blood flow in the capillaries, thus maximizing oxygenation of blood. The fine sieve structure of the gills enables them to extract oxygen very efficiently from the water although the dissolved oxygen content of water is very low.  Branchial pumping cycle The counter current flow mechanism needs a continuous unidirectional flow of water over the gill surface. This unidirectional flow of water can be created by branchial pumping. The branchial pumping cycle comprises the following phases: 1. Expansion phase (mouth opens and operculum valve closes). Water enters the mouth and causes expansion of the oral cavity 2. Compression phase (mouth closes and operculum valve opens). Water then passes over the gills by a simultaneous contraction of the oral cavity and expansion of the opercula. This makes water expelled out of the opercular opening. NB: Interruption of this cycle produces a brief reversal of flow or coughs which fish use to clear foreign matter or excess mucous from the gills. Function of the gills: 1- Respiratory function:When water is passed over the gills, oxygen is absorbed and carbon dioxide and ammonia is excreted. 2- Osmoregulation function: The gills equalize body pressures by regulating the exchange of salt and water 3- Excretion function: Mainly nitrogenous waste products such as ammonia.  The Swim (gas or air) bladder Definition It is a serous transparent blind sac contains air. Embryonic origin In fry, the swim bladder develops as a dorsal diverticulum of foregut (at the part which will form the oesophagus). The embryonic connection between foregut and bladder is through a pneumatic duct. Location Dorsal part of body cavity just ventral to vertebral column and kidney. Types of swim bladder A- According to connection with esophagus: 1. Physoclistic bladder No connection with esophagus as in Tilapia nilotica. 2. Physostomic bladder Connects with esophagus by a pneumatic duct as in Carp. B- According to number of chambers 1. Single bladder: Only one chamber as in Tilapia nilotica 2. Double bladder: Two chambers separated by a diaphragm as in Carp. The two chambers are connected by an opening controlled by a sphincter. NB: The cranial chamber in Carp and the cranial portion in Tilapia is associated with gas production and consequently has a thicker wall (but smaller size), while the posterior chamber/portion is involved in the gas reabsorption and has thin wall (but larger size). Inflation of the bladder Means entrance of gas to the bladder (a) Physostomic bladder (b) Physoclistic bladder Produced by swallowing the air Produced by release of the gases which is forced via pneumatic from the arterial blood produced duct to the bladder by special gland called gas - The release of the air from the gland which present in the bladder to outside take the lining epithelia of air bladder opposite direction NB: Gas reabsorption is made by a capillary plexus present caudal part of bladder in region called ovale. This plexus act for escaping the gases from the bladder to the circulation again. Function of swim bladder 1- Maintain fish buoyancy (vertical position in water column = suspending = floating). It acts just like a balloon – with the ability to control the amount of gas. More gas is added to the bladder enables fish to move to a higher level in the water. Gas is released from the bladder to move to a lower position in the water. Fish that do not possess a swim bladder sink to the bottom if they stop swimming. 2- Sound production (in some fishes) by movement of gases and air through the pneumatic duct with help of a powerful extrinsic muscle. 3- Excretory function; In herring fish, the bladder has a posterior opening to the exterior. 4- Determination of water depth.  How do fish swim? To be able to swim, fish need to: Overcome drag: The slime coat provides a smooth surface that allows laminar flow and minimizes frictional drag. Maintain their buoyancy : The swim bladder does this job. Maintain an upright position (balance): The fins do this job. Move efficiently: The muscles provide the power for swimming and constitute up to 80% of the fish itself. Muscle blocks (Myomeres) are arranged in multiple layers arrayed in several directions that allow the fish to move in different directions Change directions: The fins and the muscles do this job.