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Effect of dietary protein to energy ratio, stocking density and feeding level on performance of Nile tilapia in pond aquaculture

Kabir, K.A., Verdegem, M.C.J., Verreth, J.A.J., Phillips, M.J., Schrama, J.W.
Aquaculture 2019
Oreochromis niloticus, biomass, cost benefit analysis, dietary protein, dissolved oxygen, economic sustainability, energy, feed conversion, feeding level, feeds, financial economics, fish, fish production, food webs, pond culture, ponds, profits and margins, stocking rate
There is growing interest to understand the dietary P:E requirements for the supplemental feed used in tilapia pond culture where natural food contributes to production. In an on-farm trial, we tested the effect of lowering dietary P:E ratio on fish performance, pond nutrient utilization and economic benefit under two stocking densities and feeding levels. Forty ponds, (average size 234 ± 112 m2), were assigned to test the effect of two diets, which differed in P:E ratio (18 vs 14 g.MJ−1), two feeding levels (14 vs 18−1) and two stocking densities (2 vs 3 fish.m−2). Initial fish biomass was 45(±21) vs 67(±38) g.m−2 at 2 vs 3 fish.m−2, respectively. The experiment lasted 82 days. Decreasing P:E ratio enhanced tilapia production (P < 0.05; 459 vs 399 g.m−2). Increasing stocking density of tilapia from 2 to 3 m−2 increased biomass gain 43% (P < 0.001; 354 vs 505 g.m−2). Averaged over both diets and stocking densities, growth and feed conversion ratio increased with increasing feeding level (P < 0.001). Fish survival was unaffected by diet, stocking density and feeding level. Dissolved oxygen increased with increased stocking density with low P:E diet. The opposite happened for high P:E diet (P < 0.05). Increasing the feeding level also increased the DO concentration (P < 0.001). N retention efficiency was higher with the low P:E ratio diet (P < 0.001; 71 vs 52%) and decreased with increasing feeding level (P < 0.001). The data on N gain and N balance at the pond level suggest that the food web productivity was stimulated by reducing the dietary P:E ratio. The low P:E diet increased the gross margin by 95% (P < 0.001; 2076 vs 1067 USD.ha−1) and benefit cost ratio by 22% (P < 0.05; 1.57 vs 1.29). The P:E ratio of the low P:E diet is less than the presently advised. Lowering the P:E ratio from 18 to 14 g.MJ−1 in pond feeds for tilapia will increase the economic viability of pond aquaculture.