 Although the culture of snapper has been achieved in water temperatures varying from 13 o C to 28 o C, the optimum temperature for growth of snapper is 20 o C to 28 o C. Snapper stop both feeding and growing at water temperatures below 10 o C and mortalities occur if the water temperature drops below 4 o C (Bell et al 1991, Foscarini 1988). Growth is enhanced in warmer waters and may be twice that experienced in cooler locations. Therefore, it may be reasonable to assume, that increased growth may be experienced by farming fish at the northern end of their distribution in Australia (Bell et al 1991, Foscarini 1988). However, in Western Australia decreased growth has been reported in northerly populations (Moran 1992).
Dissolved oxygen levels should be maintained above 3 parts per million (ppm). Although the minimum concentration of dissolved oxygen that may be withstood is 1.5 ppm, at levels below 3.5 ppm feeding decreases (Foscarini 1988). Internationally, Pagrus auratus has been cultured in ponds, lakes, tanks, pens and sea cages. In Egypt, snapper have been successfully stocked into coastal lakes which have become saline due to evaporation and runoff from agriculture (Ishak 1980).
Tank culture of snapper utilizes large concrete tanks of 50 to 200 m³ capacity and 1.5 to 2.0 m depth (Foscarini 1988). In addition, integrated aquaculture utilizing warm water effluent from power stations has been used in Japan to provide improved hatching success, more rapid growth and more frequent spawnings (Foscarini 1988). The most common form of farming in Japan, where this species is cultured commercially on a large scale, is in floating sea cages. These growout cages are typically 10 m x 10 m and 5 to 7 m deep, with an initial mesh size of 240 to 260 square meshes per 50 cm. The net from each sea cage is replaced, to prevent fouling, with progressively larger mesh size nets every 10 days until a 1 to 2 cm diamond shaped mesh is reached (Foscarini 1988). Cages are stocked with juveniles at a density of 2,000 to 2,500 fish/m³, or approximately 6 gm/m³ (Foscarini 1988). For growout in sea cages, productivities have been reported between 1 and 8 kg/m³ (Foscarini 1988). In Japan, floating net cages are located in closed bays where they are protected from storms and strong currents, while still providing adequate flushing by tides or currents. Site selection involves surveys of currents, temperature and salinity. In addition, to ensure adequate flushing, the minimum water depth is usually twice the cage depth or 10 to 15 m (Foscarini 1988). In Japan, excess fry are sometimes released as part of fisheries enhancement or restocking programs to make up for local depletion of breeding stocks. Returns from these enhancement programs assume an initial stocking mortality of 30% due to stress. The reported returns from these enhancement programs are between 0.73% and 2.99%. Consequently, depending upon site and environmental factors, to achieve a return of 1 snapper from fish enhancement programs requires the stocking of between 34 and 137 juveniles (Smith & Hataya 1982). In order to increase return rates from enhancement programs, a number of researchers have used audio-signal training. This employs 50 to 200 hertz, 50 decibel sound waves linked with automatic feeding to condition fish to remain within a 1 km radius. This technique is, however, still experimental (Foscarini 1988, Smith & Hataya 1982). |
