cadmium induced adverse effects on fry of oreochromis mossambicus

This study investigates the effects of Cadmium (Cd) on fry of the Mozambique Tilapia Oreochromis mossambicus using standard toxicity tests. Fry were repeatedly exposed to five concentrations (0.002 – 2.0 mgl-1) of Cd and survival, growth and swimming activity were monitored over 10 days. These trials revealed that all the tested concentrations significantly enhanced mortality of the fry with concentrations above 1.0 mgl-1 resulting in 100% mortality. Mortality was positively related to the exposure level indicating dose-dependency. The LC50 1-10days ranged from 0.02 to7.26 mgl-1. Fry exposed to Cd also exhibited an increase in swimming activity in comparison to those that were not exposed indicating abnormal behaviour. Nevertheless, there was no apparent growth retardation and gross morphological defects during the brief exposure period. These findings are significant because the lethal and sublethal effects in fry were also apparent at Cd concentrations of 0.001 – 0.2 mgl-1, which are typically recorded in fresh waterbodies in Sri Lanka.