Fish Are a Major Source of Enjoyment and Food

There are approximately 34,000 species of fish in the fresh and salt waters of the world. Most fish species are cold blooded and share certain features. These features are gill slits, a skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes with the bony fishes are by far the largest class. The study of fishes is of important interest to humans in their role as a moderate but important part of the world’s good supply. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean.

Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. Almost all natural bodies of water bear fish life, with the major habitat differences being marine and freshwater. There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behavior of these animals. Specialized behavior is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. A few kinds of fishes lie on the bottom to sleep.

Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often short, usually less than a few weeks, but it can be very long. After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. Many small fishes live only one to three years. Some species may live as long as 10 or 20 or even 100 years.