Osteichthyans

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 v.s. Elasmobranchs

Osteichthyans Elasmobranchs

Has cycloid scales.

Presence of dermal bone

Operculum covers the gills

Has placoid scales

No Bones in their body

Gill Slits are exposed (Naked)

Chondrichtyes vs Osteichthyes

Skeleton

The Chondrichthyeso cartilage, composed of chondrocytes suspended in a

protein matrix.

Osteichthyes

o composed of cartilage and bone.

Scales 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.

Osteichtyeso Have cycloid or ctenoid scales.

• Cycloid scales are smooth, flat and round• Ctenoid scales posses a comb-like extensions (ctenii)

Cycloid Scales

Ctenoid Scales

Placoid Scales

Teeth Chondricthyes

o Teeth are confined to the jaws and are embedded in the gums

Osteichthyeso Teeth are not confined to the jaws

Buoyancy Chondrichtyes

o Remain buoyant by producing large amount of oil in their livers

Osteichthyeso They remain buoyant by filling their swim bladder with

gas

Swimming Chondrichthyes

o Cartilaginous fish can swim forward only

Osteichthyeso Can swim forward and backward

External

Anatomy of the Milkfish

Body divisions

HEAD

operculum

OPERCULUM

An operculum (gill cover) is a flexible bony plate protects the sensitive gills.

Branchiostegal membrane

BRANCHIOSTEGAL MEMBRANE

Membrane extending from the ventral edge of the operculum in bony fishes to beneath the jaws.

mouth

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

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

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.

Trunk and tail

Homocoercal tail (caudal fin

Maneuverability (steering) and propulsion

Dorsal fin The main purpose of the dorsal fin is to stabilize

the animal against rolling and to assist in sudden turns.

Anal fino Stabilize the fish while swimming.

Pectoral fin 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.

Pelvic fin 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.

Lateral line 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.

scale Scales serve as protection for the fish. Reduces drag during swimming.