Fish Internal Anatomy and Physiology

Objectives:1. Describe the function of major organ

systems in bony fish and list the specific organs in each system.

Digestive System

1. food enters mouth through esophagus

2. into the stomach for digestion• Typically J-curvied,

elongated, modified to grind, or lost

3. Intestine• Pyloric caecae – slender

blind tubes that secrete digestive enzymes

4. liver secretes bile that breaks down fat

Digestive Continued• Carnivorous fishes– Short, straight

intestines• Herbivorous fishes– Coiled intestine

• Sharks– Spiral valve –

increase surface area for digestion and absorbing nutrients

Circulatory System• two-chambered heart beneath the

gills• gas exchange takes place in gills• oxygenated blood is carried

through the arteries • Capillaries allow oxygen and

nutrients to reach the cells• veins carry deoxygenated blood

and carbon dioxide back to the heart

Respiratory System

Irrigation of gills

• “irrigate” – water flows over the gills

• Cartilaginous fish– Open and close the

mouth– Every gill is in its own

chamber– 1st pair of gill slits is

modified into spiracles• Allow bottom fish to

breathe

• Bony fish– Gills on each side

share a gill chamber– When mouth opens,

opercula close, pharynx expands, sucking in water

– Lamellae• Thin plates in rows

on gill filament• # of lamellae increase

with active swimmers

Respiratory System (Gills)

Nervous System• central nervous system– brain and spinal cord

• nerves connect the central nervous system with all of the organs

• sensory organs – Eyes – focus moving closer and

farther • Nictitating membrane – reduce

brightness, protect during feeding– lateral lines – sense pressure

changes, vibrations– nostrils and olfactory sacs – smell– taste buds – mouth, fins, skins,

barbels– inner ears – hearing and balance

Special Organ

• Swim bladder– Controls buoyancy– Inflates as the fish

moves up– Deflates as it move

deeper– Absorbs or releases gas

into the bloodstream