An assessment of the role of buffalo manure for pond culture of tilapia. I. On-station experiment

Abstract

Extrapolated net yields of Nile tilapia ( Oreochromis niloticus) ranged from 2.4–3.7 tonnes/ha/year (extrapolated standing stock from 1.2–1.9 tonnes/ha in the 6-month experiment) in 200-m 2 earthen ponds loaded with buffalo manure at rates of 2–6 tonnes dry matter/ha/day. Stocked fish attained a final weight of about 100 g although growth levelled off during the latter half of the experiment, which indicated that the pond carrying capacity was reached relatively quickly. The presence of the predacious snakehead fish ( Channa striata) had a marked impact on fish in certain treatments by reducing stocking density, which led to increased growth of stocked fish, and by lowering recruitment, which lowered yields. While there was a significant positive relationship between fish yield and manure input, conversion of manure to fish was inefficient with ratios of wet and dry manure to fish ranging from 71–140 and 13–25 at buffalo manure loading rates of 2–6 tonnes dry matter/ha/day, respectively; correspondingly low conversion efficiencies of buffalo manure to fish of 1.0–1.9% on a dry matter basis (manure and fish) resulted from the high dry matter loading rates of manure required to produce high nitrogen and phosphorus loading rates. Manure stained the water brown, reducing penetration of light, which may have contributed to the low phytoplankton biomass. Relatively small diel fluctuation in dissolved oxygen probably resulted from low phytoplankton biomass and increased bacterial respiration due to high manure loading rates.