The Effects of Some Agricultural Fertilizers on Fingerlings of Heterobranchus bidorsalis

The toxicity of NPK (15.15.15) and Urea fertilizers on Heterobranchus bidorsalis fingerlings (mean total length, 6.98 ± 0.30cm SD; mean body weight 2.04 ± 0.35g SD) was investigated in the present study. The fingerlings were exposed to increasing concentrations of NPK (0.00g/l - 6.25g/l), and Urea (0.00g/l - 16.25g/l) fertilizers in the static renewal bioassay for 96 hours. Exposed fish showed initial stress responses such as erratic swimming, restlessness, loss of balance, frequent attempts at jumping out of the tank and quietness. Examinations of water quality showed a reduction in the dissolved oxygen content and increase in total hardness and alkalinity as the concentrations of fertilizers were increased. After 96 hours of exposure, LC 50 , associated confidence limits and safe concentration values for NPK and Urea fertilizers were (1.09, 0.29-3.86, and 0.11g/l) and (17.84, 11.88- 13.67, and 1.78g/l) respectively. Mortality rate was noted to be concentration-dependent and death rate in the highest concentrations were significantly higher (P 0.05). The findings from this study show that both Urea and NPK fertilizers could be classified as toxic and highly toxic respectively, to H. bidorsalis fingerlings at certain concentrations.