Fish offal based aqua-feed for rearing post-larvae of freshwater prawn, Macrobrachium rosenbergii

Market demand for freshwater prawn (Macrobrachium rosenbergii) is high in Sri Lanka. The national agencies stock 20 days old post-larvae (PL 20 ) of this prawns in minor perennial reservoirs but the yield is low due to high mortality. There is a need to develop a low-cost nursing strategy for PL 20 before stocking. This research was conducted to evaluate the potential for nursing PL 20 in backyard nurseries using low-cost fish offal-based aqua-feed. The trial was carried out in a backyard nursery comprising 6 cement tanks (1.73 m 3 ) each. One hundred PL 20 were stocked in each tank (stocking density=57 PL 20 m -2 ). There were two feeding treatments each with three replicates: (1) fish offal-based aqua feed (Af), and (2) commercial prawn feed (Cf) at a rate of 5% of body weight. Af was made using a 1:1 mixture of rice bran and boiled fish-offal and Cf was purchased from the market. The feeding rate was adjusted for body weight using bi-weekly sampling and the trial was conducted for 96 days. Average Daily Growth (ADG) of PL 20 fed with Af on days 16, 30 and 47 were higher than the ADG of PL 20 fed with Cf on same days but not significantly different (p>0.05). However, ADG of PL 20 that fed on Af on day 85 and 96 were lower than that were fed on Cf on same days but not significantly different (p>0.05). Nevertheless, ADG of the PL 20 that fed on Af on day 63 (0.0038±0.0001 g day -1 ) was significantly lower (p0.05) from WG of PL 20 that fed on Af on same days. However, WG of the PL 20 that fed on Cf on days 63 and 85 (0.4551 ± 0.0784 and 1.0117 ± 0.0944 g respectively) were significantly different (p0.05) except the values on day 63 in Af (56.67±1.15) and in Cf (50.3±1.0). However, % survival of PL 20 that were fed with Af on days 85 and 96 were lower than that of the PL 20 that fed on Cf but not significantly different (p>0.05). Fish offal-based aqua-feed can therefore be effectively used for nursing PL 20 of M. rosenbergii for 47 days in backyard nurseries.