New production strategy for silver perch ('Bidyanus bidyanus'): over-wintering fingerlings in a tank-based recirculating aquaculture system

Slow growth and losses to bird predation and infectious diseases in winter can compromise the profitability of silver perch farming. To evaluate over-wintering silver perch ('Bidyanus bidyanus') in a recirculating aquaculture system (RAS), fingerlings (38g) were stocked in either cages in a pond at ambient temperatures (10-21°C) or tanks in the RAS at elevated temperatures (19-25°C) and cultured for 125 days. Mean survival (96%), final weight (146 g), specific growth rate (1.07% day⁻¹) and production rate (28.1 kg m⁻³) of fish in the RAS were significantly higher than for fish over-wintered in cages (77%, 73 g, 0.53% day⁻¹, 11.1 kg m⁻³). Fish from both treatments were then reared in cages for a further 129 days. Final mean weight of fish originally over-wintered in the RAS was 426g, while fish over-wintered in cages were only 273 g. To determine optimal stocking densities, fingerlings (11.8g) were stocked at 500, 1000 or 1500 fish m⁻³ in tanks in the RAS and cultured for 124 days. Survival was not affected, but growth was significantly slower and feed conversion ratio higher at 1500 fish m⁻³ compared with 500 or 1000 fish m⁻³. Results demonstrate that over-wintering silver perch in an RAS can produce large fingerlings for grow-out in early spring. This strategy could eliminate bird predation, reduce losses to diseases and shorten the overall culture period.