Supplementary feeding value of duckweed (Lemna sp.) at varying stocking density of Oreochromis niloticus
1990
Dhital, Raj Resham
Two iso-nitrogenous and iso-caloric diets were formulated using duckweed as a sole protein source in one (duckweed diet) and fish meal as sole protein source in the other diet (fish meal diet). Cassava starch was used as energy source in both diets. A factorial design was utilised to evaluate the feeding value of diets at three different stocking densities of Nile tilapia (3, 5 and 8 fish 1/square m) to assess the effect of density on supplementary feed requirement in fertilized tanks. The experiment was conducted in twenty seven out-door tanks for 53 day grow-out period. Growth parameters (mean body weight, total length, feed intake and specific growth rate) feed utilization (feed conversion ratio), protein utilization (protein efficiency ratio, apparent net protein utilization) and protein digestibility showed no significant difference in fish fed with duckweed diet and fish meal diet. Carcass compositions of fish were also similar except for a significantly higher lipid content of fish fed with the fish meal diet. The yield of fish supplemented with duckweed diet, fish meal diet and fertilization only differed significantly (P0.05). A yield of 4.8 g 1/square m/day was obtained with fish meal as a supplementary feed, duckweed diet had a yield of 3.9 g 1/square m/day and the lowest yield was 1.2 g 1/square m/day from only manure. Critical standing crop for manure treat tank was 231 g 1/square m Tank fertilized with manure plus inorganic fertilizer (fertilizer onward) was able to sustain only this biomass of fish. Where as treatment receiving supplementary feed, growth was not restricted.
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