Enhancing productivity of Labeo victorianus ponds using maize flour as a carbohydrate source

This study investigated the effects of manipulating carbon–nitrogen (C/N) ratio and fish stocking density on pond productivity: total heterotrophic bacteria counts, plankton biovolume and benthic macro-invertebrates. Labeo victorianus juveniles were reared for 72 days in 18 hapas suspended in six ponds measuring 150 m2 at densities of 10, 15 and 25 fish m-2. Fish in hapas received a locally formulated and prepared feed containing 295 g kg-1 crude protein, and ponds were treated with a C/N ratio of either 10 or 20. All treatments were carried out in triplicate. Increasing C/N ratio from 10 to 20 increased phytoplankton by 13% and zooplankton biovolume by 25% in the water column (P <0.001). Total benthic macro-invertebrates biovolumes were also 30% higher (P <0.05) with a C/N ratio of 20 compared to 10. Total heterotrophic bacteria counts increased both in water and sediment by 29% while net yield increased by 15% from 1534 (C/N 10) to 1821 (C/N 20) kg ha-1 72 day-1. C/N ratio of 20 and a stocking density of 25 fish m-2 led to the highest yield, survival, production and net benefits. It is suggested that polyculture may lead to better utilization of pond communities to further improve pond productivity