EFFECTS OF FREQUENCY OF GRADING ON THE GROWTH, INTRA−COHORT CANNIBALISM AND ECONOMIC BENEFITS OF AFRICAN CATFISH (CLARIAS GARIEPINUS, BURCHELL, 1822) CULTURE

The profitability of C. gariepinus still suffers from poor growth performance, low survival and high cases of cannibalism. Attempt that aims at increasing economic benefits must therefore target strategies that decouple link between catfish culture with poor growth survival and cannibalism. This study determined the effects of in−pond grading frequency on the growth performance, cannibalism and economic benefits of C. gariepinus in tank cuture system. Three treatments designated as G0 (no grading), G2 (grading every 2 weeks) and G4 (grading every four weeks) in a completely randomized design (CRD) was applied in triplicate. The tanks were stocked with 200 fingerlings each. Sampling was conducted weekly to measure length and weight of fish. Mortalities were recorded and dead fish observed under dissecting microscope to ascertain that it is due to cannibalism. An enterprise budget was conducted to determine the economic benefits of grading frequency. Data were analyzed using One−way ANOVA. Growth performance in terms of final mean weight, weight gain, Specific Growth Rate (SGR) and Food Conversion Ration (FCR) were affected by frequency of fish grading. The C. gariepinus graded every two weeks grew better than those graded every four weeks and were all above the no grading treatment. Changes in fish heterogeneity was observed after day 42 and continued until day 60. The size variation was significantly affected by grading frequency. The mean TL of fish graded every 2 weeks was the highest, followed by grading every four weeks and finally the no grading treatment was the lowest. Fish size heterogeneity (CV% and skewness) was consistently the highest in C. gariepinus in no grading treatment followed by fish where grading was done every four weeks while it was lowest in treatment where grading was done every two weeks. Mortality owing to cannibalism was affected by grading frequency where highest cannibalism mortality occurred in C. gariepinus where there was no grading followed by grading every four weeks and intermediate at grading frequency every four weeks. Meanwhile other mortality by other causes such as such as wounds and suffocation in fish did not differ with grading frequency. Highest total fish yield, net returns above TVC and TC was obtained in treatment where grading was done every 2 weeks. The enterprise budget analysis of grading frequency in the present study indicated that it is economically feasible to culture C. gariepinus when grading was done every four weeks but the best economic returns occur when the grading frequency is done every two weeks.