ECONOMIC BENEFITS OF REDUCED FEED INPUTS AND POLYCULTURE OF TILAPIA WITH MAJOR INDIAN CARPS
The aim of these studies was to determine if reductions in feed inputs and introduction of native Indian carp, rohu (Labeo rohita) and catla (Catla catla), can increase economic benefits of tilapia culture in earthen ponds in Bangladesh. Two on-station pond trials were carried out for 150 days at the Fisheries Field Laboratory at Bangladesh Agricultural University. In the first study, ponds consisting of four treatments (T1, T2, T3, and T4) with four replications each were stocked with sex-reversed Nile tilapia (Oreochromis niloticus, 5 fish/m2) without (T1) or with (T2) addition of rohu (0.25 fish/m2) and fed a full daily ration of feed (CP, 35% protein; 10%-3% body weight/day). Ponds were fertilized weekly (28 kg N and 5.6 kg P ha/week) in the other treatments and tilapia were grown in the absence (T3) or presence of Rohu (T4) at half the daily feed ration as T1 and T2. The survival rates (75-81 %) of tilapia was similar among treatments. The specific growth rate (SGR, %/day) of tilapia was higher in the T3 (1.87 ± 0.00) and T4 (1.85 ± 0.03) than the T2 (1.76 ± 0.05), and T1 (1.71 ± 0.06) groups (p < 0.05). Feed efficiency was significantly better in the T3 and T4 groups relative to those treatment fish fed the full ration. Gross production of tilapia was higher in the T4 (5,385.23 ± 276.98a kg/ha) followed by T3 (5,340.62 ± 156.47 kg/ha), T2 (4,440.99 ± 440.04 kg/ha) and T1 (4,089.83 ± 518.46 kg/ha) groups, respectively. Rohu gross production was similar among the T2 and T4 groups. A significantly higher net return (BDT 743,977/ha; benefit cost ratio of 2.92) was found in T3 followed by T4 (BDT 673,750/ha; benefit cost ratio of 2.72), T2 (BDT 286,469/ha; benefit cost ratio of 1.49) and T1 (BDT 226,675/ha; benefit cost ratio of 1.37) groups, respectively.
In the second study, ponds consisting of three treatments (T1, T2, and T3; 4 replicates each) were stocked with sex-reversed Nile tilapia (5 fish/m2) and rohu (0.625 fish/m2; T1), or catla (0.625 fish/m2; T2), or with both rohu and catla (0.32 fish/m2 and 0.31 fish/m2, respectively; T3). All ponds were fed a half daily ration of feed and ponds were fertilized weekly. Gross production of tilapia was higher in T2 (7,737.78 ± 646.51 kg/ha) followed by T1 (6,867.11 ± 570.36 kg/ha), and T3 (6,272.23 ± 183.44 kg/ha), respectively. Rohu gross production was higher in T1 and catla production was higher in T2. There was no significant difference in net return or benefit cost ratio between treatments.
Based on the higher net return and benefit-cost ratio it may be concluded that pond fertilization with feeding at half ration is substantially more cost effective over standard full feeding for growout of tilapia. Addition of major Indian carps to tilapia culture may also provide further income benefits to farmers as net production of fishes is greater in polyculture than tilapia monoculture systems regardless of the feeding regimen applied. Since tilapia growth was little impacted by feeding at half ration, but tended to grow better when polycultured with either Catla or Rohu alone compared with Rohu-Catla combined, it might be preferential to polyculture tilapia with only one of the carp species. Regardless, the results indicate profits can increase by 200% if tilapia are grown with native Indian carps and provided half the standard ration level typically used for tilapia monoculture.