Effects of stocking density on the performance of the Australian freshwater silver perch ( Bidyanus bidyanus) in cages

Abstract

Silver perch fingerlings (range mean weights, 109.3–115.4 g) were stocked at densities of 12, 25, 50, 100 or 200 fish/m 3 in cages (1 m 3) in an aerated, 0.32-ha earthen pond, with four replicate cages for each density. Fish were fed a formulated diet containing 32% crude protein and 13 MJ/kg energy and cultured for 210 days. Water temperatures ranged from 20.6 to 29.8 °C. There was aggression between fish in cages stocked at 25 or 50 fish/m 3 and survival (50% and 64.5%, respectively) was significantly lower ( P < 0.01) than at the other densities (87.5%, 98.5% and 97.4%). Stocking density did not affect final weight (454.6–471.1 g), specific growth rate (0.65–0.70%/day) or absolute growth rate (1.6–1.7 g/fish/day), but feed conversion ratios (FCR) of fish stocked at 25 or 50 fish/m 3 (4.4 and 3.7) were significantly higher ( P < 0.01) than FCRs (range, 2.3–2.5) at other densities. Coefficients of variation in weight (CV) at 25 or 50 fish/m 3 (24.4% and 28.3%) were significantly higher ( P < 0.01) than at other densities and the lowest CV of 16.1% was at 200 fish/m 3. Production was significantly affected ( P < 0.01) by stocking density, with the highest mean rate of 88.5 kg/m 3 in cages stocked with 200 fish/m 3. One infestation of the ectoparasitic ciliate, Chilodonella hexasticha, and two infestations of the monogenean gill fluke, Lepidotrema bidyana, were each treated successfully with an application of 30 mg/l formalin. The high survival, relatively fast growth, low variation in weight and high production rates of silver perch stocked at 100 or 200 fish/m 3 demonstrate that cages are a viable alternative to ponds for the commercial production of silver perch.