WHOLE EFFLUENT TOXICITY TESTING WITH ONCORHYNCHUS-MYKISS (WALBAUM 1792) - SURVIVAL AND BEHAVIORAL-RESPONSES TO A DILUTION SERIES OF A MINING EFFLUENT IN SOUTH-AFRICA

Survival, behavioral early warning responses to, and behavioral effect s of a complex effluent from Richards Bay Minerals in Natal, South Afr ica, were studied using rainbow trout Oncorhynchus mykiss (Walbaum 179 2) as a biosensor. Three replicates of eight juvenile fish were expose d to a dilution series of the effluent (0, 5, 10, 20, 50, 75, 100%) an d the behavioral pattern (ventilation, locomotion) was measured online with quadropole impedance conversion. Survival decreased with increas ing effluent concentration. Before death, 0. mykiss coloration darkene d, demonstrating skewed bodies subsequently after death. Decreased act ivity and increased ventilation combined with increased ventilation fr equency were found within the first 2 h of exposure at greater than or equal to 96-h LC50 value of 10% effluent concentration indicating ear ly warning responses. During 4 days of exposure, activity decreased an d ventilation increased further at concentrations around the 96-h LC50 value indicating toxic effects.