Quantitative and qualitative aspects of fish crop in relation to environmental quality

The effects of environmental quality on the quantitative and qualitative aspects of fish crop are reviewed with reference to fisheries in rivers, lakes, reservoirs, and coastal waters ranging from the temperate zone to subtropical areas in mainland China. The mechanism of these effects is discussed, and the insidiousness of long-term exposure to low-concentration pollutants to fish stock is stressed. Regarding the assessment of the effect of pollution on fish, most of our information has been derived from laboratory studies, in which the antagonistic or synergistic action between multiple pollutants was scarcely taken into consideration. One has to be cautious when the results of laboratory experiments are extrapolated to the realistic natural environment. It is advocated that surveys and tests concerning the relation between environmental quality and fish life be made on natural waters in addition to laboratory studies, and the effects be elucidated at the individual level, population level, and the ecosystem level.