The Effect of Dietary Protein Levels and Female Brood Stock Size On Size Heterogeneity Among Heterobranchus longifilis Fingerlings

ABSTRACT

Background and Objectives: Heterobranchus longifilis and its sister species and corresponding hybrids are popular species cultured in the Sub-Saharan Africa. Studying the size variation of this species will help maximize product output and enhance aquaculture production, thus, the objective of this work was to assess how female brood stock size and dietary crude protein levels influence fingerlings size heterogeneity and at the same time seek for ways of obtaining better seed quality and survival in Heterobranchus longifilis culture. Materials and Methods: The experiment was conducted in a randomized factorial design with 4 brood stock size categories (size category 1-4) and 4 dietary protein levels (protein level 45, 40, 35 and PL 30%) in 3 replications. The fish in each replicate were fed twice daily at 3% bwt per day with the respective feed for the particular treatment combination for 6 months. Water exchange was maintained by daily intermittent flow through and the quality monitored weekly. After determination of the 3 best ripe fish for spawning, each fish was induced with Ovaprim at 0.5 ml kg^-1 bwt and 50 g egg aliquot fertilized with 1 ml of pooled milt from 16 homogenous males of 2,181.83 g mean bwt. 250 one day old larvae from each female were raised separately for 30 days. Each set of fingerlings was audited, sorted into sizes, survival rate, and percentage composition of each class of fingerlings determined. The growth performance and FCR of the brood stock in each replicate were also determined. Four size categories of fingerlings A, B, C and D in descending order of size were identified. The data generated were subjected to analysis of variance for significant difference and means separated with DMRT at p = 0.05. Results: The results revealed significant interaction for mean wt gain, SGR, and FCR of brood stocks, and composition of C and D fingerlings. No significant interactions were found in survival rate, and percentage composition of A and B fingerlings. Conclusion: Size heterogeneity of fingerlings appeared to be strongly maternal size dependent as a greater percentage of bigger larvae were obtained from larger maternal brood stock.