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 ElasmobranchsHas cycloid scales. Has placoid scalesPresence of dermal No Bones in their bone bodyOperculum covers the gills Gill Slits are exposed (Naked)
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
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.
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.
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.