Suitability of Using Duckweed as Feed and Treated Sewage as Water Source in Tilapia Aquaculture (original) (raw)

Feasibility of using both treated effluent and duckweed biomass from a pilot-scale UASB-duckweed ponds system treating domestic sewage was evaluated in rearing Nile tilapia (Oreochromis niloticus). The nutritional value of duckweed was compared with wheat bran, used as a local fish feed ingredient, by applying these as the only source of feed for tilapia juveniles weighing 20 grams initial mean body weight. Two sources of water were used for each feed trial, treated-sewage and freshwater. The experiment was conducted in parallel with a conventional settled sewage-fed fishpond stocked with tilapia. Results of growth performance demonstrated that, in case of freshwater ponds specific growth rate (SGR) of tilapia fed on fresh duckweed was significantly (p < 0.01) higher than the SGR in wheat bran fed pond. No significant difference (p > 0.05) was observed between the two feeding regimes in case of treated sewage-fed ponds. The SGR of tilapia reared in the treated sewage-wheat bran-fed pond (TWP) was significantly higher (p <0.01) than the SGR in the freshwater-wheat bran-fed pond (FWP). On the other hand, due to the early spawning in the treated sewage-duckweed-fed pond (TDP) SGR of tilapia in the latter was significantly lower (p <0.05) than the SGR in the freshwater-duckweed-fed pond (FDP). The results demonstrated that duckweed-fed ponds provide higher net fish yield (11.8 ton/ha/y in TDP and 9.6 ton/ha/y in FDP), than wheat bran-fed ponds (8.9 ton/ha/y in TWP and 6.4 ton/ha/y in FWP). The fish yields in the ponds fed with treated sewage were higher than those in the ponds fed with freshwater. Negative net yield was observed in the settled sewage-fed pond (SSP) at -0.16 ton/ha/y. The negative results obtained in this pond, were attributed to the high mortality of 60% in the adult fish and 38% in the fry during the autumn. The best result was obtained in the treated effluent-duckweed-fed fishpond, providing 11.8 ton/ha/y net yield, which shows the potential value of both treated sewage and duckweed in aquaculture of tilapia.