Effects of dietary P:E ratio and Rhizoclonium in two stocking densities on growth and profitability of Nile tilapia in intensive pond culture

Abstract

Two onsite tests were carried out to determine the effects of varying dietary protein to energy (P:E) ratio in intensive culture of Nile tilapia in two different places at two stocking densities. In both field trials, three diets were used namely commercial (CM) diet, control (CO) diet containing no Rhizoclonium and a diet containing Rhizoclonium replacing 52% of soybean meal (RLP); the diets contained decreasing P:E ratio of 21, 16 and 12 gMJ-1, respectively. The first trial was conducted in Aklan, Philippines at a stocking density of 17 fishm-2 while the second was in Pangasinan, Philippines at 27 fishm-2. In both trials, the three diets were fed for 2 months to 3 replicate cages of Nile tilapia, all of which were randomly placed in about 1.0 ha fresh water fish pond. In the first trial in Aklan, at 17 fish m-2 stocking density, no significant differences in the parameters were observed except in the absolute growth rate (AGR) in which the RLP dietary treatment exhibited a higher value than did either the CM or the CO diet. In Pangasinan, at 27 fish m-2 stocking density, significant differences in TFI, DFI and SGR were observed, all the other parameters were statistically similar. The RLP group exhibited lower total feed intake (TFI) and daily feed intake (DFI) but higher specific growth rate (SGR) than did either the CM or CO diet. In either stocking densities, feed cost was the main determinant of profitability in which the RLP group resulted in significantly highest profitability i.e., lowest total production cost, highest gross income and highest profit and profit margin. Although profit was significantly higher in the higher stocking density, profit margin was significantly higher in the lower stocking density. There was no statistical interaction between dietary treatment and stocking density as analyzed by two-way analysis of variance.