Implications of Size Heterogeneity and Food Availability on the Survival of Heterobranchus Longifilis Fingerlings

This experiment was conducted for a period of 90 days to evaluate the effects of size heterogeneity and food availability on the survival rate of the fingerlings of Heterobranchuslongifilis. The experiment took place in 48 netting hap as each measuring 80cm X 250cm and 110cm deep placed in 6 concrete tanks measuring 3mx8mx1.2m with flow through. 720 fingerlings ranging from 20mm to 60mm total length were used in six size ratios of smaller to large fingerlings to give 1:1; 0.833:1; 0.667:1; 0.50:1; 0.40:1 and 0.33:1. There were 5 predators and 10 preys in each treatment set except the treatment with ratio 1:1 which had 15 (100%) predators. Four feeding regimes of 2 in a day, 1 in a day; 1 in 2 days and 1 in 4 days were taken as food availability using a 35% crude protein polluted feed. The experiment was a 6 by 4 factorial with two replications in a complete randomized design. The fish were fed at 1.5% body weight per ration based on their respective feeding regimens and adjusted accordingly bi-weekly after weight measurement. Feeding was done accordingly at 600-700 hrs (all categories) and 1800-1900hrs (for those fed twice daily). Evidence of cannibalism was monitored regularly. Water quality parameters were monitored weekly. Survival rate was determined at the end of 90 days and the data analyzed using analysis of variance for significance difference. Evidence of cannibalism was observed across all size categories. There was significant interaction between size heterogeneity and food availability. The highest survival rates were found in size ratios 0.833:1-1:1 fed twice daily and these were recommended.