Comparative Effect of Different Stocking Densities of Heteroclarias on Plankton Abundance in Tarpaulin Tanks

The effect of different stocking densities of hybrid catfish (Heteroclarias) on plankton abundance in tarpaulin tanks was studied for a period of six (6) months (January – June 2016). The study employed Complete Randomized Design (CRD) experimental design. Five different stocking densities (treatments) were employed (T1 = 100fish/m2 , T2 = 75fish/m2 , T3 = 38fish/m2 , T4 = 18fish/m2 and T5 = 9fish/m2). These were replicated three times. Filtration technique was employed. Mesh size plankton net (25µm) was used to filter 10L depth integrated water samples. The water samples (net content) were emptied into a wide mouth plastic container and preserved in 5% formalin solution after proper labeling. The samples were then taken to the laboratory and were allowed to stand for at least 24hrs in the laboratory for the plankton to settle. The samples were pipetted (1ml sample) with sample pipette. The content was placed in a Sedgewick-Rafter plankton-counting chamber and examined under a magnification of 500× and 1000×. The plankton were identified, enumerated and total number of species were also recorded using keys and check lists. For phytoplankton, a total of eighty-three (83) species belonging to six (6) taxonomic groups were observed in the experimental tanks. Bacillariophyceae occurred highest and was represented by thirty-six (36) species. Chrysophyceae and xanthophyceae occurred least with one (1) species respectively. For zooplankton, a total of twenty (20) species belonging to four (4) taxa were identified during the study. Cladocera occurred highest with nine (9) species, while protozoa occurred least with two (2) species. T5 (9fish/m2 ) had the highest abundance of phytoplankton and zooplankton. T1 (100fish/m2) had the least abundance of phytoplankton and T2 (75fish/m 2 ) had the lowest abundance of zooplankton. Therefore, a stocking density of 9fish/m2 of heteroclarias is optimal and is recommended in order to maintain better plankton presence and good environmental condition.

Keywords: Heteroclarias, hybrid catfish, phytoplankton, zooplankton, stocking density.