Fish are major components of most aquatic habitats; there are thousands of species in streams, rivers, lakes, estuaries, and marine environments. They also are an important source of food and recreation, and are key elements in many natural food webs. They affect the physicochemical properties of the systems in which they occur; interact with plankton, macrophytes, and other aquatic organisms; and can serve as environmental indicators.
Fish share many physiological processes with mammals and are used in both the laboratory and the field by the environmental manager and health specialist in biological assays.1 Changes in the composition of a fish assemblage often indicate variation in pH, salinity, temperature regime, solutes, flow, turbidity, dissolved oxygen (DO), substrate composition, or pollution level. The gain or loss of certain species is a common consequence of environmental change. Because fish are conspicuous, they are often sentinel indicators of the toxification of streams, lakes, and coastal waters. In extreme cases, dead or moribund fish may adversely affect the potability and recreational use of waters and create foul odors.
In addition, fish are the focus of economically important sport and commercial fisheries; licensing fees for both private and commercial sectors provide funds for state and federal agencies. Because fish are both ecologically and economically important, there are often intense commercial and recreational interests surrounding their harvest and study. As a result, there is a need for scientists, often supported by public funds, to arbitrate such competing interests.