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activity 5 - Osteichthyes

The document discusses the key anatomical features of bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes). It describes that Osteichthyes have bones and cycloid or ctenoid scales, while Chondrichthyes have cartilage and placoid scales. It then explains the functions of various fins, the lateral line, scales, eyes, nostrils, mouth, gills, operculum, and other parts in fish anatomy.

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 All bony fishes  Familiar descendants of tetrapods  Characterized by an air sac that can be secondarily lost  Large units of dermal bone can be found on the head and shoulder girdle  The group is subdivided based on the structure of paired appendages (fins)
Osteichthyans Elasmobranchs Has cycloid scales. Has placoid scales Presence of dermal No Bones in their bone body Operculum covers the gills Gill Slits are exposed (Naked)
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 The Chondrichthyes o cartilage, composed of chondrocytes suspended in a protein matrix.  Osteichthyes o composed of cartilage and bone.
 Chondricthyes o large scales called placoid scales • Scales have a bone like base embedded in the skin and a backward projecting enamel covered dentine spine.  Osteichtyes o Have cycloid or ctenoid scales. • Cycloid scales are smooth, flat and round • Ctenoid scales posses a comb-like extensions (ctenii)
 Chondricthyes o Teeth are confined to the jaws and are embedded in the gums  Osteichthyes o Teeth are not confined to the jaws
 Chondrichtyes o Remain buoyant by producing large amount of oil in their livers  Osteichthyes o They remain buoyant by filling their swim bladder with gas
 Chondrichthyes o Cartilaginous fish can swim forward only  Osteichthyes o Can swim forward and backward
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operculum
 An operculum (gill cover) is a flexible bony plate protects the sensitive gills.
Branchiostegal membrane
 Membrane extending from the ventral edge of the operculum in bony fishes to beneath the jaws.
mouth
 The mouth serves for taking in food; also for the breathing current of water.  It has a small mouth that does not extend to eye.  They are toothless fish.
nostrils
 The nostrils of fish do not open into the back of the mouth as do those of mammals, and are not, therefore, for breathing.  They lead into organs of smell which are as a rule, very sensitive, so that a fish can detect the presence of food in the water at considerable distances.
eyes
 Fish see through their eyes and can detect color.  The eyes are rounder in fish than mammals because of the refractive index of water and focus is achieved by moving the lens in and out, not distorting it as in mammals.
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 Maneuverability (steering) and propulsion
 The main purpose of the dorsal fin is to stabilize the animal against rolling and to assist in sudden turns.
o Stabilize the fish while swimming.
 The paired pectoral fins are located on each side, usually just behind the operculum, and are homologous to the forelimbs of tetrapods.  It assists in maintaining depth as the fish swims.
 The paired pelvic or ventral fins are located ventrally below the pectoral fins. They are homologous to the hindlimbs of tetrapods. The pelvic fin assists the fish in going up or down through the water, turning sharply, and stopping quickly.
 The lateral line is a sense organ used to detect movement and vibration (mechanoreceptors) in the surrounding water. In most species, it consists of a line of receptors running along each side of the fish.
 Scales serve as protection for the fish.  Reduces drag during swimming.