Marine fishes exhibit a great diversity of sizes, shapes, and behaviors, ranging in size from an inch long goby to a 25 foot long great white shark. Shapes can be unique, such as the spiny box fish, or typically fish-like, such as the red snapper. Fishes can be categorized by their habitats, which are as diverse as the fish species themselves.
Pelagic fish are those species that spend their time in the open ocean. Pelagic species include sardines and jack fish, which are known to associate in large schools. Some pelagic species get very large and are solitary hunters, such as the adult bluefin tuna and swordfish. As juveniles and small adults, these species exhibit schooling behavior, becoming solitary as they mature.
Coral reef fish are, obviously, fish species that are typically associated with coral reef habitats. Many of these fish have evolved especially to associate with coral, such as the parrot fish, that crunches hard coral in order to eat the soft-bodied coral animal inside its calcium carbonate home. Butterfly fish have very small, pointed mouths that allow them to pick small particles from the coral, including the soft coral animals. The coral reefs of the world exhibit an incredible diversity of fish species that are typically brightly colored and make up the majority of marine fish found in the aquarium trade.
Estuarine fish are species of fish that are typically found in estuaries, which are coastal areas where fresh and salt water come together. Species of fish found in estuaries must be able to tolerate wide shifts in salinity and temperature, since their habitat is known to be extremely variable. Estuarine species in the southeastern U.S. include flounder, seatrout, mullet, and drum.
Reef fish are typically associated with areas where the bottom topography is uneven, often with deposits of limestone or other rock forms. While these areas are significantly different from coral reefs, the species associated with them are known as reef fish, and include a variety of snapper and grouper species, triggerfish, porgies, among a variety of others.
Some species of fish require both nearshore and offshore habitats to satisfy their life history requirements. The red drum is one of the most popular, sought-after species in the recreational fishery of the Southeastern U.S. Large adult red drum inhabit marine waters offshore and mate, and spawn their eggs there. The eggs are moved by currents to nearshore areas where they hatch. The young red drum stay in estuaries until their second or third year, before moving offshore to join the adult spawning stock. Another important species that utilizes nearshore and offshore habitats is the gag grouper. Such multiple habitat requirements of fish species complicate their life cycle and can make management difficult.
