Determination of 96-hr LC50 and lethal responses of Wallago attu to water-borne chromium

(Importance)Water pollution by heavy metals, especially chromium pollution from industrial source can affect aquatic life, all ecosystems and human health directly or indirectly through food chain. The present research work was conducted under laboratory conditions to determine 96-hr LC50 and lethal responses of a fish, Wallago attu, to water-borne chromium. (Brief Method) The fingerlings of fish were kept in glass aquaria having 35-L water capacity. The toxicity tests were conducted at constant total hardness (250mgL-1), water temperature (28 ºC) and pH (8) with three replications for each test concentration, separately. Physico-chemical parameters of water viz. total hardness, temperature, pH, carbon dioxide, dissolved oxygen, total ammonia, sodium and potassium were monitored twice a day during each 96-hr trial. The 96 hour LC50 and lethal concentrations of chromium, with 95% confidence interval, were computed by using the Probit analysis method. Regression/correlation analyses were also performed to find-out relationships among different variables under study. (Results/key findings) This investigation revealed significant differences between 96-hr LC50 and lethal concentrations of chromium for Wallago attu. The mean 96-hr LC50 and lethal concentrations of chromium for this fish were computed as 59.17±1.45 and 90.65±1.09mgL-1, respectively. (Conclusions)The present investigation also revealed that metallic ion concentrations had significant impacts on the physico-chemical parameters of the test media as total ammonia and carbon dioxide contents showed significant increase with concomitant increase in chromium concentration while dissolved oxygen showed significant decrease. The dissolved oxygen revealed negatively significant relationship with total ammonia. Calcium exhibited statistically highly significant but negative relation with magnesium contents of the test media.