Biology: Fish Anatomy and Habitat

Body Shape and Locomotion

• 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.

Scales and Skin

• 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.

Jaws and Teeth

• 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.

Mouth and Feeding

• The shape of the mouth is an important clue to a fish's food source.
• Fish with large mouths eat whole fish or chunks of fish.
• Fish with small mouths nibble on plants and small animals.
• Fish with ventral mouths eat on the bottom.
• Fish with dorsal mouths eat near the surface.

Internal Organs

• 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.

Air Bladder

• 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 Senses

• 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.