Performance of Nile tilapia Oreochromis niloticus fingerlings in a hyper intensive recirculating aquaculture system with low water exchange

Abstract

The aim of this paper was evaluate the performance of Nile tilapia fingerlings ( Oreochromis niloticus ) raised at hyper intensive stocking density in a recirculating aquaculture system (RAS) with minimum water replacing. The experimental system was performed in a single-batch nursery system to obtain 50 g fish size in 60 days. Fish (2.07 ± 0.04 g) were stocked in triplicate at 400 (T1), 500 (T2) and 600 (T3) fish m -3 (0.84, 1.05, 1.22 kg m -3 ). RAS functioned with 12,000 L of recirculating water and 252 L day -1 of water replacing (2.1% daily). The efficiency of the biofilter for removing the total ammonia nitrogen (TAN) was 48 ± 12.5 mg L -1 . Stocking density did not affect significantly the survival (89.5 to 93.6%). The growth rate of T1 (0.96 g day -1 ; 5.01% day -1 ) and T2 (0.92 g day -1 ; 4.95 % day -1 ) was significantly higher than T3 (0.83 g day -1 ; 4.80% day -1 ). The specific growth rate (SGR)of T1 was 41% influenced by temperature. For T2 and T3 the SGR were influenced by the variation of dissolved oxygen (DO) that explained 47 and 44% of the fish weight variation, respectively. The SGR from T3 was also affected by the concentration of ammonia nitrogen (31%). The high stocking density affected the overall size of fish and the size homogeneity, but had no negative effect on the length–weight relationship (L-W). Data support the conclusion that fingerling stocked at 400 and 500 fish m -3 shows high performance during 9-weeks when the biomass not exceed 37 kg m -3 . At this time fish have reached the desired final nursery weight (50 g) for transfer to grow-out facilities.