Abstract:
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.
