A morphometric study of effects of nickel, chromium and cadmium on the secondary lamellae of rainbow trout gills

Rainbow trout were exposed in a constantly-flowing hard water for 3.5 days to concentrations of nickel and chromium at about 0.05 and 0.2 respectively, of the 48-h LC50 for this species, and for 234 days to cadmium at about 0.001 of its 48-h LC50.Morphometric measurements were made of structural components of the gill secondary lamellae from fish, both immediately following their removal from the test solution and at various intervals (up to 21 days) during which they were kept in “clean” water.Diffusing capacities were calculated and indicated changes in the ability of fish to transfer oxygen from the water to the blood. Only nickel appeared to have a marked harmful effect, and recovery to normal diffusing capacity occurred within 21 days.Following the chromium and cadmium treatments, statistically significant changes were not detectable but possible trends were indicated. In the case of cadmium, some suggestion of an increase in diffusing capacity at the lowest concentration (0.002 mg l⁻¹) was observed.