Acute Toxicity and Stress Behaviour of Heterobranchus bidorsalis Exposed to the Detergent Nittol ® NTL

The acute toxicity of the detergent Nittol ® 0.8, 1.0, 1.2, 1.4, 1.6, and 0.0 mg NTL/L of clean water on Heterobrunchus bidorsalis , 5.5 ± 0.3 g, 6.4 ± 0.5 cm were investigated, using semi-static bioassay, for 96 h in 50 L capacity plastic test bowls. The fingerlings of the same brood stock and age were collected from Onose Farms Limited, Ughelli, Delta State to the University Research Laboratory, Enugu Lat. 7.4 N; 8°7′5 and long 6°8′ E. 7°6′ W. The test fish were acclimatized for 14 days, and fed at 3% body weight once daily, on a 40% CP commercial diet. Feeding was suspended 24 h before and during the range finding and acute tests. The whole set-up was replicated three times, and no death was recorded during the acclimatization period and in the control. A total of 180 fingerlings were used, and 10 fingerlings were assigned to each replicate. The test set-up was monitored daily for water quality parameters, opercular ventilation, tail fin beat frequency, and mortality. Dose and time-dependent behavioural patterns exhibited by the test fish, during the exposure periods include rapid swimming, air gulping, loss of balance, and a period of convulsion before death. Significant elevation in pH and temperature, reduction of DO compared to the control ( p < 0.05) in the water quality, and dose-dependent early elevation of the tail and fin movements declined towards the end of the experiment. The 96 h LC 50 was determined to be 1.41 mg/L, indicating that the detergent NTL is toxic to the test fish. The haematological parameters were significantly ( p < 0.05) reduced in the treated ranges of RBC 5.20 ± 0.07–8.00 ± 0.02 × 10 6 mm 3 , HB 7.53 ± 0.50–10.72 ± 0.14 g/dl, PCV 13.20 ± 0.8.50–18.00 ± 0.43 % below their elevated respective controls of 10.50 ± 0.01 × 10 6 mm 3 , 11.00 ± 0.01 g/dl, and 23.48 ± 0.2.6 %. The white blood cells (WBC) recorded a significant ( p < 0.05) increase in ranges of 23.72 ± 0.14–51.80 ± 1.9 × 10 3 mm 3 above the control value of 11.00 ± 0.01 × 10 3 mm 3 Therefore, values greater than the safe amount of 0.014 mg/L should not be allowed in the receiving culture waters for Heterobrunchus bidorsalis fingerlings.