Effect of density on growth and survival of ornate rock lobster, Panulirus ornatus (Fabricius, 1798), in a flow-through raceway system

Juvenile ornate rock lobsters (Panulirus ornatus) (3.24 +/- 0.09 g; 13.8 +/- 0.13 mm CL) captured from the wild were stocked at three densities ( 14, 29, and 43 m(-2)) within each of four 4000-L fibreglass raceway tanks with flow-through seawater supply. Lobsters were provided with shelters consisting of opaque polyethylene platforms, 600 mm x 600 mm, supported on six 100-mm legs and were fed continually through the night with a commercial penaeid prawn (P. japonicus) pellet supplemented with prawn flesh once per day. Growth and survival were monitored by means of a monthly sample of 20 lobsters from each experimental unit. After 272 days, density treatments did not differ significantly in survival, which averaged 52.5% (+/-2.8). Lobster size was also unaffected by density, and mean size for all lobsters was 225.3 +/- 4.68 g (61.8 +/- 4.7 mm CL) at harvest. Mortality was consistent through time and was almost entirely attributable to cannibalism of postmoult individuals. The cannibalism may have been due to inappropriate shelter and feeding strategy. Despite higher mortality than anticipated, growth was rapid, representing a specific growth rate of 1.56% day 1, sufficient to permit growth from g to 1 kg within 18 months. The experiment confirmed the excellent potential of P. ornatus for commercial aquaculture.