Comparative study of the growth of Oreochromis niloticus and Sarotherodon galilaeus in sewage ponds

Abstract

Tilapia is a delicacy and of economic importance among freshwater capture fisheries. Some of these tilapia species are Oreochromis niloticus and Sarotherodon galilaeus. O. niloticus has better growth rate in fresh water culture than other tilapine species such as the S. galilaeus . However, due to pollution risk, sewage water might not support the growth of O. niloticus or any other tilapia species. The method used in this study was to assess the quality of physio-chemical parameters of sewage water in each of the sewage treatment ponds alongside the growth of O. niloticus and S. galilaeus in the ponds. The aim of this researech was to compare the growth of O. niloticus and S. galilaeus cultured in 1 m3 by volume of 1 mm net size mounted in the sewage treatment ponds in Tamale (Ghana) without supplementary feeding. The water quality was monitored every 2 weeks for six months to assess the levels of temperature, pH, turbidity, dissolved oxygen and ammonia. The overall mean weight of O. niloticus (19. 8 g) was higher than that of S. galilaeus (14. 0 g). The average growth rate of O. niloticus was higher (0. 13 g/day) than that of S. galilaeus (0. 12 g/day). Both O. niloticus and S. galilaeus in the aerobic pond showed a superior average growth rate of 0. 21 g/day and 0. 20 g/day respectively than fishes in the other ponds. Mean Dissolved Oxygen remained high (5. 9-7. 6 mg L -1 ) in all the ponds throughout the study. Biological oxygen demand values between 3. 2 mg L -1 and 18. 9 mg L -1 were observed in the ponds between January and September. Ammonia-nitrogen or ionized Ammonia ranged from 1. 1 mg L -1 to 10. 0 mg L -1 . The minimum and maximum turbidity values in the ponds ranged from 32-480 NTU. High concentrations of toxic (un-ionized) ammonia exceeding 2. 0 mg L -1 occurred in all the ponds at certain times of the study and led to the death of O. niloticus and S. galilaeus.