Fish Internal Anatomy and Physiology Objectives: Describe the function of major organ systems in bony fish and list the specific organs in each system.
Digestive System • food enters mouth through esophagus • into the stomach for digestion • Typically J-curvied, elongated, modified to grind, or lost • Intestine • Pyloric caecae – slender blind tubes that secrete digestive enzymes • 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
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
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