Developmental instability in grayling (Thymallus thymallus) exposed to methylmercury during embryogenesis

Embryos of grayling, Thymallus thymallus, were exposed to water with different concentrations of methylmercury (0, 0.16, 0.8, 4.0, 20 μg Hg liter−1) during egg development. After hatching they were reared in control water for 3 years. The exposure resulted in body concentrations 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 effect 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 populationʹs morphological norm (i.e. a measure of morphological variability). There was no effect of contamination 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 may be uncertain estimators of the level of sub-lethal stress.