Fluctuating asymmetry in fishes inhabiting acidified and unacidified lakes

Abstract

Fluctuating asymmetry, the random deviation from perfect bilateral symmetry owing to developmental perturbation, has been used in a number of studies to quantify stress during early life. Decreasing pH and related changes in aquatic environments owing to input of anthropogenic acids have been demonstrated to be physiologically stressful to many fish species. Therefore, a link between environmental acidification and fluctuating asymmetry was postulated. Brook trout (Salvelinus fontinalis), white sucker (Catostomus commersoni), and lake chub (Couesis plumbeus) were collected from lakes over a wide range of pH values. Use of several species allowed separate consideration of environmental and genetic effects. Depending on species, 15 to 20 paired meristic and morphometric characters were scored for the left and right sides of each individual. Differences between sides were calculated and analyzed by a variety of statistical methods. Most characters examined were not significantly more asymmetric in acidified lakes. However, one or two characters in each species were more asymmetric in lakes of lower pH. Relative overall asymmetry in brook trout was related to parameters that changed with acidification. The small number of locations sampled precluded such an analysis in the other two species. The results are consistent with the hypothetical link between environmental stress by acidification and increased fluctuating asymmetry, but the connection is much weaker than expected. This finding, the need for large sample sizes, and the lack of a definite causal link, severely limits the utility of this type of analysis in assessing the level of stress in fish populations.