|Studying Water Pollution through Fish Assessment (Indian Institute of Sciences)|
This study revealed that large scale mortality has occurred among fish species like Eutroplus suratensis, Chanda ranga, Puntius sp., Nandus nandus and Amblypharyngodon mola. Investigations into the limnological parameters revealed not much deviation from the usual values for this region with water temperature 28°C, water transparency 31 cm, free carbon di-oxide (FCO2) generally absent, water ph 7.683 (avg: average) and 0.570 (Sd: standard deviation), water conductivity 0.397 (avg) and 0.07 (Sd) milli mhos/cm. However, dissolved oxygen (DO) was recorded, very low at 2.6 and an average of 3.025 (Sd:0.076) mg/lit during the period of fish-kill. Estimation of nitrite and nitrate revealed 0.229 (avg) and 0.054 (Sd) and 1.374 (avg) and 0.477 (Sd) mg/lit; Phosphorous was 7.055 (avg) and 2.925 (Sd) mg/lit.
Analysis of the bottom soil revealed medium acidic pH (5.90), normal conductivity (0.07 milli mhos/cm), low available phosphorus (3.068 kg/acre) and low available potassium (17.5 kg/acre). There had not been any prolific growth of aquatic macrophytes in the lake and plankton density was also usual during the period of fish mortality.
Estimation of trace elements through atomic absorption
spectrophotometry revealed a low quantity of lead and cadmium in both water and
soil, mercury was not detected. The results of chemical analyses shows that, in
water lead quantity was 0.47 ppm and cadmium
0.04 ppm and in soil lead content was 0.55 ppm and cadmium 0.05 ppm.
These studies reveal that the fish-kill in Sankey Lake was due to sudden and considerable fall in DO levels in some locations (due to sewage let into the lake) resulting in asphyxiation and was not due to any kind of infection because none of the fishes showed any symptom of disease. Steps are to be taken for the conservation of this biotope, which not only provides a recreational spot for the tourists, but has also been serving as one of the potential sites for stocking, hybridisation and cage culture of the Indian major carps.