Abstract

Any adverse change in the environmental conditions affects the life of aquatic organisms in water. Fish death was suddenly observed in Lake Kabo. To investigate its cause and look for solution, a research team started to consider the Lake. The present study was conducted to identify the reason for the fish deaths that accidentally occur in the lake. To achieve the objective samples were collected from four different sampling sites on the lake from October 2017 to August 2018. The four sampling stations on the lake were selected based on criteria and were coded. Sample collection was made every month. Data were analyzed using SPSS version 23. Experimental activities were carried out both on the spot and in laboratory. The results analyzed were compared with permissible limits prescribed by WHO, FAO, BIS and other references. In this study, the pH (6.1-8.7), total dissolved solid (TDS) (60-251.3 mg/L) and total alkalinity (101-195 mg/L) of the lake followed the prescribed limits set by WHO (1993) and BIS (1991). Critical dissolved oxygen (DO) value (2.8-4.7 mg/L) and temperature (T°) (25-30°C) of the lake were found below the specified limit for tilapia Fish. In this study, the reasons for the sudden death of tilapia fish in the lake include: highly fluctuated values of T°, DO and pH value of the lake water especially in rainy season. The study concluded that tilapia fish could not tolerate the fluctuation of DO value which is less than 3 mg/L. The result from secchi-disk also supported the less value of DO. The mean nutrients values for Ca++, PO4-3 and (Cl-) of the lake were 7.6 ± 2.6, 0.1039±0.15 and 1.5102±0.7 mg/L, respectively. The reduced level of DO and extreme fluctuation of pH were the expected reasons for the sudden fish death in the lake during rainy season.

Key words: Lake Kabo, pH, dissolved oxygen (DO), total dissolved solid (TDS), Secchi-disk.