GROWTH PERFORMANCE OF NILE TILAPIA, GREENHOUSE GAS EMISSIONS AND MICROBIAL WATER QUALITY ASSOCIATED WITH COMPOSTED CHICKEN MANURE FERTILIZATION IN PONDS

Abstract

In the recent past fish farming has gained great prominence in Kenya as the Country struggles to meet food security. Nile tilapia (Oreochromis niloticus L.) farming has attracted the most demand, with the use of manure to enhance primary productivity in fish ponds being encouraged as a form of increasing productivity and returns to the investment. The objective of this study was to assess the role of Composted Chicken Manure pond fertilization on growth performance of Nile tilapia, greenhouse gas emissions and bacterial levels. Generally, there is paucity of such information originating from sub- Saharan Africa. 1,000 Nile tilapia whose average weight was 0.5 g and total length 1.9 cm were stocked in 300 m2 Unfertilized ponds (UF), inorganic fertilized ponds (IF) and Organic fertilized ponds (OF). A control experiment was set up to evaluate the effect of using Composted Chicken Manure (CCM), where 50 Nile tilapia whose average weight was 0.4 g and length 2.4 cm were stocked in square tanks of 1.5 m length and 1 m water height in five treatments of Unfertilized tank (UF), CCM at 10, 20 and 30 g m-2, and non-composted (LPM) at 20 g m-2. Results showed that there were significant differences (p<0.05) among the mean weights and lengths of fish at the end of the growth period, with the fish in the IF treatment having the highest mean weight and mean length. However, the specific growth rate did not show any significant differences among the different treatments. The value of regression coefficient b of 2.57 to 3.14 revealed isometric growth in all the treatments. Relative condition factors ranged from 1 in IF to 1.14 in UF. The mean CH4 fluxes for UF ponds was 0.010±0.012 mg m-2h-1; 0.025±0.020 mg m-2h-1 in IF ponds and 0.059±0.094 mg m-2h-1 in OF ponds; with CH4 fluxes in UF being significantly lower (p<0.05). Mean fluxes of CO2 did not show significant differences among the treatments with mean flux of 0.216±0.407 mgm-2h-1 in UF ponds; 0.227±0.278 mgm-2h-1 in IF ponds and 0.334±0.454 mgm-2h-1 in OF ponds. Mean fluxes of N2O lacked difference, with UF ponds having mean flux of 0.003±0.175 μgm-2h-1, 0.032±0.056 μgm-2h-1 in IF ponds and 0.093±0.324 μgm-2h-1 in OF ponds. The Total Plate Count for bacteria and Escherichia coli did not show significant difference, whereas Total coliforms showed significant differences (p<0.05). In the control study, mean weights of Nile tilapia were significantly higher in CCM20, CCM30 and LPM20 (p<0.05). CO2 and N2O fluxes in UF ponds were significantly lower, while CH4 fluxes showed no significant differences. TPC, TC and E. coli were significantly higher in LPM20 (p<0.05). Fertilization of fish ponds improved the growth of Nile tilapia, increased CH4 emissions and increased bacterial levels, an observation that calls for mitigation measures towards reduction of the emissions and the microbial levels. It also displayed the ability of composted manure in improving growth performance of Nile tilapia, reduction of greenhouse gas emissions and reduction in the number of bacterial levels, with CCM30 represented the best case to be adopted as an aquaculture technology, innovations and management practice (TIMP). The study gives a baseline on GHG emissions arising from fish pond fertilization, and offers a novel manure product that can mitigate on the emissions and bacterial levels.