Respiratory Stress of Sub-Lethal Concentration of Chlorine on Oreochromis niloticus

Abstract

In aquatic environment, one of the most significant manifestations of the toxic stress on aquatic organisms, especially fishes are the over stimulation or depression of respiratory activities. These variations in respiratory activities have been used as in indicator of environmental stress. This study was aimed to assess the sub-lethal toxicity of chlorine through respiratory stress on Oreochromis niloticus. It was noticed that in all dosage experiments as the concentration increased rate of gill movement decreased. The rate of gill movement during the first minute after the dosage in control was 128 per minute. Serial dilution method employed in this study helped to assess the LC50 of chlorine and the value noted was 2 ppm. The minimum number of gill movement noted was in 20ppm dosage and the value was 98 per minute whereas the maximum noted was in 5ppm dosage and the value was 101 per minute. In 60th minutes after dosage also the control showed a value of 126 per minute and 20 ppm dosage showed a very low value such as 32 per minute whereas 5ppm dosage of chlorine showed a reasonably good value of 61 per minute. It was noted that in the case of average gill movement, control showed a very high value such as 127 per minute, whereas 5ppm dosage of chlorine showed a reasonably good value such as 84 per minute, and 20 ppm dosage showed a low value 72 per minute. When a comparison was made between control and differently dosed fishes, it was observed that in all dosed cases the average gill movement was very low when compared with control. A significant difference exists between gill movement in the dosed group and control (P<0.05). Consumption of oxygen increased with an increase in dosage and decreased with increased period of exposure. In control the average oxygen consumption was 0.012 mg/ml/gm body weight, in 5ppm it was 0.014 mg/ml/gm body weight, in 10 ppm it was 0.0155 mg/ml/gm body weight, in 15 ppm it was 0.021 mg/ml/gm body weight and in 20ppm it was0.022 mg/ml/gm body weight.