Download - activity 5 - Osteichthyes
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.