Effect of fish overwintering in earthen ponds and RAS treatment on growth performance of the Nile tilapia, Oreochromis niloticus

The present work aimed to enhance the tolerance of juvenile Nile tilapia, Oreochromis niloticus against cold stress and increase their survival rate by using the recirculating aquaculture system (RAS) during the winter season. The overwintering experiment was carried out in 3 earthen ponds, each of 1 feddan (as replicates of the control group); and 3 circular fiberglass tanks at an intensive fish farm, located in Nubaria City, Beheira Governorate, Egypt. The indoor 1000-liter circular fiberglass tanks (as replicates of recirculating aquaculture system, RAS treatment group). The experiment extended from December 2018 to April 2019. Results showed that the Nile tilapia fingerling reared in the recirculating aquaculture system (RAS) exhibited values of growth performance parameters (L_f, LG, DLG and G in L, W_f, WG, DWG, G in W and SGR) higher than that of fish fingerlings reared in control earthen ponds. The growth performance parameters were significantly varied between all tanks of the RAS treatment and that of control ponds. Also, the feed utilization parameters were best for fishes reared in RAS treatment tanks than that reared in earthen ponds. The survival rate recorded in RAS aquaculture was very high (90.0± 5.0 %) and it was very low (17.1± 1.474 %) in control earthen ponds. The economic analysis showed positive net income values (1080, 840 & 600 LE) for RAS Tanks 2, 1 & 3, respectively. But, negative net income values were recorded (-34200, -30650 & -30010LE)for earthen ponds 3,2 & 1, respectively.