Rabbitfish (Siganus guttatus) culture in floating net cage with different stocking densities

Abstract

Rabbitfish (Siganus guttatus) is a schooling species which potential for being farmed in high density, however the information about stocking density of this species remain rare. This study was aimed to evaluate growth, survival rate, FCR, stress level and osmoregulation of Rabbitfish under different stocking densities. The tested fishes were the second generation (G2) of Rabbitfish that produced by hatchery outdoor of Research Institute of Coastal Aquaculture and Fisheries Extension, Maros, Indonesia. There were two stages of this study: the first stage was fingerling production. The seeds of Rabbitfish with average of length 6.2±0.8 cm and body weight 4.7±1.9 g/ind were reared in total of 12 units of 1 x 1 x 1 m3 floating net cage for 90 days. The stocking densities were 50, 100, 150 and 200 ind/m3. The second stage of this study was fish growing, where the tested fishes were cultivated with stocking density of 100, 150 and 200 ind/m3 in the same size of net as the first stage. The result of first stage showed that stocking density did not significantly affect growth rate of Rabbitfish fingerling. However, survival rate at stocking density of 50 (99.33±1.15%) and 100 ind/m3 (98,33±0,58%) were higher compared to stocking densities 150 and 200 ind/m3 (94.89±1.39 and 93.50±2.65%, respectively). The result of second stage showed that stocking density of 100 ind/m3 resulted significant growth, survival rate and FCR compared to that observed on 150 and 200 ind/m3. The fish stocked with density of 100 ind/m3 had length (18.6±0.3 cm), weigh (121.8±9.8 g/ind.), survival rate (92.0±2.6%) and FCR (4,41±0,43). Whereas, the result for fish stocked with 150 ind/m3 were 17.6±0.3 cm, 107.1±7.0 gram, 86.2±7.1 % and 5.15±0.59, respectively, and 200 ind/m3 were 16.9±0.2 cm, 96.5±5.9 gram, 82.2±2.3 % and 5,64±0,6, respectively. High stocking density might trigger stress on Rabbitfish and lower blood osmolality found on stocking density of 150 ind/m3 (490.00±59.77 mOsm/kg) and 200 ind/m3 (469.00±23.30 mOsm/kg) compared to that observed on density of 100 ind/m3 (501.67±23.50 mosm/kg). During hypo-osmotic condition, the osmoregulation was not regulated by stocking density as indicated by blood osmotic performance levels <1, which was 0.37 mOsm/kg (100 ind/m3) and 0.33 mOsm/kg (for 150 and 200 ind/m3).