Fish and humans are not as different as you may believe!

Fisheries Biology: Fish Anatomy — The Inside Story

From Florida Fish and Wildlife Conservation Commission

Fish anatomy

Fish and humans are not as different as you may believe!

You probably think that you're very different from the fish you pursue. They live in lakes; you live on land. You breathe air; fish breathe underwater. And you face each other from very different ends of a fishing rod! But when you take a closer look on an anatomical level, anglers and fish are more similar than they are different. Here are some of the internal features of the fish, most of which they share with us. A largemouth bass destined for the frying pan makes an excellent specimen because this species is large enough for easy examination. For anglers brave enough to do some investigating while filleting their next fish, a fascinating learning experience awaits!

Lateral Line  One of the fish’s primary sense organs; detects underwater vibrations and is capable of determining the location of their source.

Muscle  Provides movement and locomotion. This is the part of the fish that is usually eaten, and composes the fillet of the fish.

Kidney  Filters liquid waste materials from the blood. Extremely important in regulating water and salt concentrations within the fish’s body, allowing certain fish species to exist in freshwater or saltwater, and in some cases (such as snook or tarpon) both.

Pyloric Caeca  This organ with fingerlike projections is located near the junction of the stomach and the intestines. It secretes enzymes that aid in digestion.

Spinal Cord  Connects the brain to the rest of the body and relays sensory information from the body to the brain, as well as instructions from the brain to the rest of the body.

Spine  The primary structural framework upon which the fish’s body is built; connects to the skull at the front of the fish and to the tail at the rear.

Peanut

Brain  The control center of the fish. All sensory information is processed here. A bass brain is about the size of a shelled peanut! Remember this humbling fact the next time you return home skunked.

Swim (or Air) Bladder  A hollow, gas-filled balance organ that allows a fish to conserve energy by maintaining neutral buoyancy (suspending) in water.

Eggs  In adult female bass, the bright orange mass of eggs is unmistakable during the spawning season, but is still usually identifiable at other times of the year. The male organs, which produce milt for fertilizing the eggs, are much smaller and white but found in the same general location.

Stomach and Intestines  Break down (digest) food and absorb nutrients. Fish such as bass that are piscivorous (eat other fish) have fairly short intestines because such food is easy to chemically break down. Fish such as tilapia that are herbivorous (eat plants) require longer intestines because plant matter is usually tough and fibrous and more difficult to break down.

Vent  The site of waste elimination from the fish’s body.

Liver  Assists in digestion by secreting enzymes that break down fats. Also important in maintaining proper blood chemistry and waste excretion.

Heart  Circulates blood throughout the body. Oxygen and digested nutrients are delivered to the cells of various organs through the blood, and the blood transports waste products from the cells to the kidneys and liver for elimination.

Gills  Allow a fish to breathe underwater. These are very delicate and should not be touched if the fish is to be released.

If many of these terms sound familiar to you, you should have a better appreciation for the kinship you share with your fellow creature, the fish!

Illustration modified from Duane Raver, Jr.