Fish and Crustaceans

About Fish and Crustaceans

The earth has been home to aquatic animals for more than 480 million years. Today, there is a vast diversity of aquatic wildlife with animals having life spans ranging from a few weeks to 50 years or more.

Fish

Fish are fascinating individuals. With tens of thousands of different species, their behaviors, habits and abilities vary wildly. Some fish have taste buds on their lips, and some use their mouths to build homes and even take care of their children. For instance, some father fish carry eggs in their mouths until the babies hatch. Others open their mouths and let their babies swim inside if their safety is threatened. Some South African fish lay their eggs on leaves, which allow them to carry the eggs to a safe location. Some fish learn to avoid danger by noticing other fish ensnared by nets. Dr. Phil Gee, a psychologist from the University of Plymouth, says that "fish have a memory span of at least three months," and they "are probably able to adapt to changes in their circumstances, like any other small animals and birds."

Oxford University scientist Dr. Theresa Burt de Perera has found that fish possess cognitive abilities that exceed those of some small mammals. Studying blind Mexican cave fish, Burt de Perera found that, rather than simply avoiding objects in their tank, the fish create a "mental map" and memorize the obstacles in their surroundings. The fish are then able to use this "mental map" to recognize changes in the way these obstacles are arranged, a feat that hamsters cannot perform.

Fish do not sleep like humans do—most lack eyelids, so they never close their eyes—but to give their bodies a break from swimming, some fish float in place, some build a nest, and some wedge themselves into the mud or coral.

Even though fish live in the water, they still need to clean themselves. In fact, certain small fish do the job for bigger animals. Larger fish will swim to "cleaning stations" where "cleaner fish" will inspect their bodies, removing and eating parasites and other materials off their skin. The cleaner fish even swim into the mouths of the larger fish to clean their teeth of food particles.

Crustaceans

Aquatic animals aren't only fish, of course. Crustaceans—such as shrimp, lobsters and certain crabs—are characterized by their jointed appendages and hard shells.

Lobsters live for about 15 years, and some may live to be 100. The biggest known lobster caught weighed more than 44 pounds. These animals have a pair of pincers called chelapeds, or claws, one being a heavier crusher claw and the other a smaller feeding claw. When lobsters grow, they have to molt, or shed, their shells and grow new ones. Interestingly, the lobster eats the old shell.

Most adult lobsters live in the ocean, anywhere from 10 to 600 feet beneath the water's surface. Despite their poor vision, lobsters are able to navigate these dark and shadowy areas. The lobster's entire body acts as a sense organ; tiny hairs that cover the body are sensitive to touch. They also have "hedgehog hairs" along the inside of the pincers on their walking legs. These short bristles serve them similarly to the way our taste buds work. If a lobster likes the taste of something these bristles detect, the food is passed along to her or his mouth.

Lobsters also possess a short set of antennae called "antennules," which allow them to receive chemical signals carried by the seawater. Delicate hairs on the antennules have more than 400 types of sensitive "chemoreceptors." According to Dr. Jelle Atema of the Marine Biological Laboratory in Woods Hole, Mass., these chemical receptors "may enable the animal to detect the species, sex, and even the mood of another animal."

Lobsters are primarily scavengers. Their typical diet is comprised of clams, crabs, mussels, and worms, but a lobster may eat up to 100 different kinds of animals and also some plants.

Many people think lobsters are cannibalistic because they have only observed lobsters in captivity. In the wild, lobsters will not typically eat other lobsters unless they are in crowded conditions or find a particularly vulnerable lobster who has just molted and is waiting for the new shell to harden. The crowded conditions in which captive lobsters must live enhance the risk of cannibalism.

Dr. Robert Steneck of the University of Maine has videotaped lobster behavior and notes that lobsters, sensitive to human presence, can be studied better when they don't know they're being watched. Steneck conducted an experiment in which he formed "lobster condos," tight formations created with PVC pipes. With a camera running, he was able to observe the animals' responses to living in close proximity. Some lobsters took up residence in individual "condos" and, soon, a large male began "evicting" smaller lobsters from their dwellings. In most instances, the dominant lobster would abandon the "condo" after establishing his superiority.