Optimum rabbit density over fish ponds to optimise Nile tilapia production in an integrated rabbit–fish system in Rwanda

Abstract

Although previous studies have suggested that rabbit excreta can be used as high-quality manure for sustaining plankton production due to their gradual nutrient release, integrated rabbit–fish production systems are still not widely used. Between 2006 and 2010 optimal rabbit densities for sustainable integrated rabbit–Nile tilapia farming were investigated at the Rwasave Fish Farming and Research Station, Rwanda, by assessing the effects of various rabbit densities on plankton type and abundance, fish production and pond water quality. Five treatments, using 200, 400, 800, 1 200 and 1 600 rabbits per hectare of pond, were tested over ponds in replicates. Physicochemical water parameters, plankton and fish growth were monitored on a daily and/or bi-weekly basis. Fish yield was positively correlated with rabbit density up to 1 200 rabbits ha−1 of pond, but at greater densities the yield began decreasing with increasing inorganic nitrogen, especially ammonia, and decreasing oxygen. Phytoplankton biomass, based on Chl a concentration, and daily primary productivity increased with increasing rabbit densities. Optimum density was in the range of 800 to 1 200 rabbits ha−1 of pond. A density of 1 200 rabbits ha−1 of pond gave the highest fish yield, 3.3 t ha−1 y−1 and the lowest ammonia level, and 800 gave the best environment for fish and plankton in terms of concentrations of Chl a and dissolved oxygen.