BIO-ECONOMIC EVALUATION OF AFRICAN CATFISH (CLARIAS GARIEPINUS) INTERACTION WITH NILE TILAPIA (OREOCHROMIS NILOTICUS) IN LOW INPUT SYSTEM AND ITS EFFECT ON WATER QUALITY
Gamal El Naggar , Ahmad Nasr-Alla and Nabil A. Ibrahim
WorldFish Center, Regional Center for Africa and West Asia, Abbassa, Abou-Hammad, Sharkia, Egypt.
Received 2/ 8/ 2010 Accepted 31/ 8/ 2010
The present experiment was conducted in twelve earthen ponds 2100-m2 at WorldFish Center, Abbassa, Egypt, to assess the efficiency of African catfish (Clarias gariepinus) in controlling unwanted Nile tilapia (Oreochrmis niloticus) recruits and its effect on water quality, in addition to evaluate the economics of tilapia (T) and catfish (CF) biculture under low-input production system (fertilized only ponds). Mixed sex tilapia fry (0.15 g) were stocked at a rate of 2 fish m-2 and African catfish fingerlings (223 g) were stocked two months later at stocking rates of 0, 7 and 13% of tilapia (T. only, T.+7%CF and T.+13%CF, respectively). Ponds were fertilized using chicken litter at a rate of 500
kg ha-1 week-1 for 30 weeks. Water quality parameters were monitored weekly for measuring dissolved oxygen concentration, water temperature, Secchi disk depth, pH and total ammonia nitrogen (TAN), while nitrate-nitrogen, available phosphorus, chlorophyll “a”, and total hardness were measured biweekly. Among mean water quality parameters only pH and available phosphorus were differed significantly (P<0.05) among treatments. The other water quality parameters were not significantly different (P>0.05), although non significance mean TAN concentration was 1.5 folds in T. only treatment than other polyculture treatments. At the end of the experimental period, catfish significantly (P<0.05) reduced the biomass of tilapia recruits to 14.9 and 8 % fry as percentage of the total fish yield in T.+7%CF and T.+13%CF treatments, respectively as compared to 26.6% obtained in T. only.
Total fish production was
also significantly (P<0.05) higher in T.+13%CF and T.+7%CF compared to T. only treatment. But marketable size tilapia production in T.+7%CF and T.+13%CF (1617.3, 1725.9 kg/ha, respectively) was significantly lower than tilapia monoculture “T. only” (1865.5 kg/ha). Partial economic analysis showed that there were no significant differences among the different treatments for both net profit and rate of return on operational costs. This study concluded that the presence of catfish with tilapia reduced TAN concentrations to about two thirds of tilapia monoculture, while introduction of catfish at a rate of 13% of tilapia stocking number eliminated 70% of tilapia reproduction and enhanced total pond production of marketable size fish
since it was 2804.2 kg/ha while it was 2427.3, 1887.5 kg/ha for T.+7%CF and T. only treatments, respectively. But profit generation rates didn’t show significant differences among the different treatments.
Keywords: African catfish; bio-economic; biological control; low input system and tilapia.