INDIVIDUAL VARIATION IN THE SWIMMING PERFORMANCE OF FISHES - AN OVERLOOKED SOURCE OF VARIATION IN TOXICITY STUDIES

A commonly used indicator of sublethal stress in fish is impaired swim ming performance. Analysis of performance data usually employs a simpl e comparison, in which the mean of a stressed group of fish is compare d to that of a control group. Although such a comparison is satisfacto ry in many cases, a comparison emphasizing individual variation in per formance can yield valuable information unattainable by a means compar ison. In this experiment, we determined critical swimming speeds of su badult male fathead minnows before and after exposure to contaminated sediments from Devil's Swamp, Louisiana, USA. The data were then analy zed using a means comparison and an individual approach to illustrate the differences in explanatory power between the two approaches.