Biology: Fish Anatomy and Habitat

Study Notes

Fish body shape is a compromise among factors like locomotion, feeding, and staying alive.
The caudal (tail) fin is responsible for propulsion in most bony fish.
Fish with continuous caudal fins can swim in and around cracks and crevices, and maintain a rapid speed for long durations.
Fish with lunate caudal fins tend to be the fastest swimmers.
Fish with truncate caudal fins are usually strong, but slow swimmers.

Most bony fish have skin covered with bony scales that look like shingles on a roof.
Scales come in different types, including thick and hard ones, and small overlapping ones.
Some fish, like catfish and paddlefish, lack scales on their body.
Glands in the skin secrete a layer of mucus that covers the entire body, protecting fish from infection.
Mucus also helps maintain a higher salt content than in the surrounding water.

Teeth can be present on the roof of the mouth, tongue, and jaws.
Some fish, like minnows and suckers, lack teeth in the jaw but have "throat" teeth behind the gills to tear or crush food.
Pharyngeal teeth are found in some fish, like goldfish.
Filter feeders, like paddlefish, shad, and bigmouth buffalo, have weak jaws and teeth, but their gills have hair-like structures that strain food from water.

Most fish have recognizable organs like heart, stomach, intestines, liver, spleen, kidneys, and gonads.
The sex of most fish can only be determined by looking at the gonads.
Carnivorous fish usually have a short gut with a white or silvery lining in the body cavity.
Herbivorous fish have a long, coiled intestine and a black lining in the body cavity.
The air bladder or swim bladder is an outgrowth of the intestinal tract, found only in ray-finned fishes.

The air bladder helps fish control their density.
Fish must be the same density as the water to stay afloat.
Sharks are denser than water and sink if they stop swimming, but gain additional buoyancy by storing large amounts of oil in their huge livers.

Fish possess the five major senses: hearing, smell, taste, sight, and touch.
Hearing is accomplished through the inner ear, sometimes aided by the air bladder.
Smell is highly developed in many fish, and they detect odors through the nares located between the eyes and in front of the snout.
Taste is an important sense for fish, and they can have taste buds outside the mouth.
Sight: Fish are near-sighted due to the optical qualities of water.
Touch and the Lateral Line System: Fish possess a sense of "distant touch" through the lateral line system, which detects vibrations and pressures on the surface of the fish.