External Anatomy of Fish PDF

External anatomy of fish Are there any differences in anatomy and physiology between fish and land animal???????  General characters of fish: - Fish are poikilothermic or ectothermic or cold-blooded animals living in water. This is due to absence of the thermo-regulator...

External anatomy of fish Are there any differences in anatomy and physiology between fish and land animal???????  General characters of fish: - Fish are poikilothermic or ectothermic or cold-blooded animals living in water. This is due to absence of the thermo-regulatory center and their body temperatures is dependent on the temperature of the surrounding water ( ±0.5 ) which explains the high food conversion in fish when compared with the land animals (low food conversion ratio). Fish are extremely efficient in converting feed into high-quality protein. On average, farmed fish require 1.1 kg of feed to gain 1 kg of body mass, compared with 1.7 kg for poultry and 6.6 kg for cattle. Fish are anatomically and physiologically adapted to live in aquatic environment. Therefore, it is fully differing from the atmospheric environment. It does not have bone marrow and lymph nodes, the main components of immune system in mammals, so fish are more susceptible to disease than mammals.  The hemopoietic organs are anterior kidney, liver and spleen. Fish as an aquatic cold blooded animal having limbs represented by fins and takes its oxygen from water by gills  External anatomy Classification 1-Morphological 3-Integumentary 2-Regional types of fish system and Body anatomy of (shape of the appendages fish body) 1) Morphological types of fish (shape of the body)  Unlike other invertebrates (land animals), a wide variation in fish shapes is demonstrated. The shape of the fish body plays an important role in swimming behavior and survival of fish in their habitat.  There are different body shapes as follows:- a) Fusiform or torpedo-shaped body:- The most rapid swimmers among fish salmon, tuna and mackerel. tuna salmon b) Compressiform (laterally compressed):- as cichlids and Nile perch orechromis niloticus c) Depressiform (dorso-ventrally compressed) : as catfish(clarias gariepinus) Catfish d) Anguilliform (eel shaped):- Eel fish e) globi-form tetraodon fahaka 2) Regional anatomy of fish Three main body regions are easily distinguished grossly, namely head region (anterior part), trunck region (middle part) and tail region (posterior part)  a) Head region It is the most anterior part of fish body, extends from the mouth tip anteriorly to the posterior margin of the gill cover (operculum) posteriorly.‫ظ‬. the anterior organs of digestive system (mouth opening, mouth cavity and pharynx). respiratory system (gills and gill cover).  nervous system (brain and spinal cord). sensory organs (eyes, nostrils and barbels in some fish some important regions as most, (occiput dorsally and isthmus region Ventrally).  Head area can be subdivided into 3 areas:- Snout: Area between eyes and anterior tip of the mouth. Occiput: The dorsal area extending from naris to the level of opercula opening. Isthmus: The ventral narrow area between the two gill openings. 1-Mouth opening:- (It is usually situated at the anterior end of the head) Terminal position (Both jaws are the same length) Cichlids (Fish having a terminal mouth are generally mid-water feeder)  Sub-terminal position (The lower jaw is slightly shorter than the upper jaw) Catfish (Fish with sub-terminal and inferior mouths are usually bottom feeders)  Inferior mouth (The lower jaw is shorter than the upper jaw) Shark  Superior mouth (the lower jaw is longer than the upper jaw) Pike ( fish with this type of mouth feed at the surface) Note:- in some fish species the mouth has membranous part which has the ability to protruded forming tube help the fish to suck its prey from a distance,in tilapia. 2) teeth:- According to position:- 1) Maxillary teeth........................ on the upper jaw. 2) Mandibular teeth ……………… on the lower jaw. 3) Palatine teeth (pharyngeal).......... on the palatine bone. According to shape of teeth:- 1) Canine teeth...................... Hydrocynus forskahlii. 2) Needle like teeth................ Nile nilotica. 3) Saw like teeth..................... Saurus. Acc. To presence of teeth:- a) Toothed fish: Permanent teeth ……… as in eel and shark. Temporary teeth……….. as in tilapia. b) Toothless fish: as in common carp and grey mullet. Some fish as cyprinids, have no teeth in their mouth but only behind. These are called pharyngeal teeth, which are used for mastication and cutting the food up before it descends into the stomach. 3) Barbels:- Tactile and taste organs used for locating food in dark or muddy waters. They are located at upper and lower lips. They carry chemical, taste and touch receptors, and used mainly during the dark times as a sensory organ. Barbels may be simple and short as in carp or long and complex as in catfish.  The maximum number of barbels is 4 pairs, which are one pair of nasal barbels near the nostril, one pair of maxillary barbels on the upper jaw and 1-2 pairs of mandibular barbels on the lower jaw. simple and short barbels in carp long and complex barbels in catfish 4) Eyes:- Usually, one eye on each side of the head. The eyes neither have lids nor lashes.  In some fish the two eyes are located in the same side as in flatfish such as Solea or Flounder. In some fish species such as southern cave fish, eyes are absent. Solea (flounder) fish southern cave fish The fish eye is large and has a spherical, hard lens which placed close to the front of the eye and bulges through the pupil, so ensuring a wide field of vision. 5) Nostriles:- One or two nares on each side of the snout leading to closed sac and function as olfactory organ of fish not for respiration. b) Trunk region:- It extends from the posterior margin of operculum to the caudal peduncle. The trunk of fish includes some important topographical areas as:- Nuchal region (the dorsal surface just behind the occiput), Breast (the ventral area just behind the isthmus), Belly (the area behind the breast), caudal peduncle (the constricted part separating the trunk c) Tail region :- The fish tail is located posterior to the caudal peduncle and is composed of caudal fin. branchiostegal rays:- thin bones located just posterior and ventral to the gill covers that support the gill membranes. The number of branchiostegal rays is useful for distinguishing certain species of fish. 3) Integumentary system and body covering:- a) Integumentary organ or Skin :- It covers the fish body and is considered the first line of defense against diseases.  It is either covered with scales or scaleless. Histologically, the different known layers of fish skin are cuticle, epidermis, and dermis. 1) Cuticle layer:- It is mainly composed of mucopolysaccharides that formed largely from epithelial surface. It contains specific immunoglobulins, lysozymes and free fatty acids that usually lyse the invasive micro- organisms. 2) Epidermis layer:- It is the cellular layer of skin and composed mainly of stratified squamous epithelial with mucous secreting cells, club cells (alarm cells), macrophages and lymphocytes. 3) Dermis layer:- It contains pigment cells (chromatophores), mast cells, scales pockets, blood vessels, nerves and sensory nerve endings. The significant importance of the skin: - 1)Protection:- Skin provides the first line of defense against micro-organisms through:- a. Intactness: Intact skin is the first physical barrier against invasion of bacteria, fungus, viruses, and parasites. b. Scales c. Mucous coat 2) Skin has osmoregulatory, execratory and respiratory functions. 3) Coloration:- Skin contains sensory and chemo- receptors in addition to pigment cells (chromatophores) b) Scales :- Are translucent plates of dermal origin that project into the epidermis forming a protective barrier for fish. Scales are often overlap each other with the free margin directed towered the tail in a manner that minimize friction with the water. Types of scales :- 1-cycloid scales 2-ctenoid scales oval with smooth edges, as has fine comb-like teeth on in cichlids their free edges, as In rock 3-Ganoid scales 4- placoid scales As in polypetrus fish As in shark Types of scales :- 1-cycloid scales 2-ctenoid scales 3-Ganoid scales 4- placoid scales Functions of scales :- 1)Protection:- scales act as physical barrier.  If fish accidentally lost some of their scales, they are often attacked by bacteria and fungi.  Moreover, scale-less fish such as catfish, can be much more sensitive to drugs and toxins in water. 1)Helping in classification and identification:- Scales distribution is different from fish species to other. Fish covered totally with scales are known as “scaly fish” as tilapia.  While some fish are covered partially with scales called “partially scaly” fish as mirror carp.  Some kinds of fish are naked and having no scales “scaleless fish” such as catfish and bayad. 3)Aging:- Fish age can be determined from their scales which form year rings.These rings are formed because growth is uneven, fast in summer, slow in winter. During the winter a fish grow a little and only a narrow dark band will show on the scales.  Summer growth result in a broad light ring and these, separated by the preceding winter zone, and is counted as a year ring so can give the age of the fish. 4)Helping on spawning determination:- (spawning marks in salmon) c) Mucous coat :- Mucous secreted by mucus cells in the epidermal layer has the following actions: 1)Contains immunoglobulins which have antimicrobial action (IgM) 2)Contains lysozymes (proteolytic action) 3)Contains fatty acids (acidic PH which is unsuitable media for the growth of microorganisms) 4)Wearing and tearing of the mucous coat inhibit colonization of micro-organisms on the integument as on skin, gills and also on GIT mucosa 5)Contains bacteriolysins. 4) Body appendages :- I) The fins II) lateral line system  I) The fins 2-Unpaired 1-Paired (single) fins: fins:- -  1-Paired fins:- b) Pelvic fin a) Pectoral or ventral fins fins a) Pectoral fins:- Structure and location :- Composed mostly from soft rays as in tilapia, while in catfish they contain spines. Located usually behind the posterior margin of operculum on each side of the fish body.  Functions :- 1)Pectoral fins are used as oars for slow swimming or precise orientation and for sudden braking. 2)The pectoral fins carrying taste buds and touch receptors, acting as a sensory organ for fish. b) Pelvic fin or ventral fins:- Structure and location:- composed mostly from both soft and hard rays.  The pelvic fins are found in the ventral aspect of fish body but varied in their placement, being thoracic as in tilapia, abdominal as in Mugil cephalus or sub abdominal as in common carp. Functions:- 1)Stabilizing and braking of fish during swimming. 2) It contains touch receptors for protection. 3)They used as a supporting limbs in some bottom feeder fish.  2-Unpaired (single) fins:- a) dorsal c) Tail fin or fin or back b) anal fin caudal fin fin a) Dorsal fin or back fin:- Structure and location:- Composed from either soft or hared spins or mixed soft and hard rays. Located in the dorsal aspect of fish body. Functions:- The functions of dorsal fin (s) appear to be in stabilizing of fish during swimming, helping to achieve quick change of direction. Types:- 1)It may be single and long one, extends all over the back as in tilapia. 2)Small and short, as in grass and silver carp. 3)It divided into two parts, and the two parts either have the same structure as in mugil and sea bass or differ in their structure (one fleshy and the other is soft rays with spines ) as in bagrus bayad and salmon. b)Anal fin:- Structures and location:- It composed mostly of soft and hard rays and located ventro- posterior to the vent.  Functions:- 1) Help in braking of fish during swimming in conjunction with the caudal and dorsal fins. 2)It contains touch receptors. 3) It modified to copulatory organ as in mosquito fish (Gambosia fish) c) Tail fin or caudal fin:-  Structure and location:- It composed mostly of soft rays without spines and located in the posterior part of the body and connected to the body through caudal peduncle Function:- Its function is a power swimming organ. Shape:- In fact, the shape of caudal fin is correlated to the swimming habits of fish.  In speedy fish, the caudal fin takes crescent or lunate shape with narrow caudal peduncle as in salmon.  Fish with forked caudal fin are constant swimmer as in bayad. Fish with truncate, round or emarginated caudal fin are strong swimmer but slower than those mentioned before as in tilapia and catfish.  II)lateral line system:- Definition:- The lateral line is a series of sense organs, small open tubes penetrating the scales and connected by a canal filled with slime. It runs along the side of the body to the tail. Types:- It may be single as in carp or double as in tilapia. Functions:- 1)It detects minute electrical currents in the water; also, it can detect the chemical substances and any vibration in the water. The small differences in pressure in the open tubes of the lateral line, caused by the disturbances are registered by nerves, and the message is released to and decoded by the brain, which anatomically estimate their direction and distance of the object. This means that the fish, through its lateral line pores is constantly receiving a picture of its immediate surroundings. Blind fish, even carnivorous fish, can survive by the sensitivity of the lateral line. THANK YOU