DEVELOPMENTAL INSTABILITY IN GRAYLING (THYMALLUS-THYMALLUS) EXPOSED TO METHYLMERCURY DURING EMBRYOGENESIS

Embryos of grayling, Thymallus thymallus, were exposed to water with d ifferent concentrations of methylmercury (0, 0.16, 0.8, 4.0, 20 mu g H g liter(-1)) during egg development. After hatching they were reared i n control water for 3 years. The exposure resulted in body concentrati ons in the newly hatched fry of 0.01, 0.09, 0.27, 0.63 and 3.80 mg Hg kg(-1) wet wt, respectively. In this paper we test if there is an effe ct of the level of methylmercury exposure on developmental stability. We did this by measuring both the level of fluctuating asymmetry (FA) and the departure from the population's morphological norm (i.e. a mea sure of morphological variability). There was no effect of contaminati on level on FA, whereas there was a slight increase in departure from the morphological norm in the more contaminated groups. This indicates that the level of FA or the departure from some morphological norm ma y be uncertain estimators of the level of sub-lethal stress. (C) 1998 Elsevier Science Ltd. All rights reserved.