The effect of different holding systems and diets on the performance of spiny lobster juveniles, Jasus edwardsii (Hutton, 1875)

This study evaluated the growth and survival of lobster juveniles over 8 months when fed fresh Perna canaliculus mussel and stocked at a density of 35 ind. m−2 in one of three holding systems: a prototype sea-cage design, a commercial sea-cage design, and small experimental land-based holding tanks. At the same time the growth, survival and nutritional condition of lobsters fed fresh mussel in the prototype sea-cages were compared with lobsters feeding only on the biofouling of the sea-cages or fed two artificial diets (dry and moist) three times a week. Survival in the prototype sea-cages (83.3±2.3%) was similar to the experimental flow-through tanks (87.9±8.0%) but significantly higher than the commercial sea-cage (55.4±1.8%). Furthermore, the prototype sea-cages resulted in significantly higher specific growth rate (SGR=0.96% BW day−1) than the other system designs (flow-through tank SGR=0.86 BW day−1 and commercial sea-cage SGR=0.77% BW day−1). The growth rate in the prototype sea-cages was one of the fastest ever recorded for this species, over this size range of juveniles (3–31 g) and at comparatively low seawater temperatures (15.2 °C). The survival of lobsters in the prototype sea-cages did not differ between the three experimental feeding regimes. However, growth when feeding on biofouling alone or with the addition of artificial diets was comparatively inferior to the lobsters fed mussels (SGR=0.96% BW day−1; survival=83.3±2.3%). Lobsters fed the dry formulated diet (SGR=0.78% BW day−1; survival=79.3±1.2%) grew significantly faster than on the moist formulated diet (0.60% BW day−1; 59±17.8%) or on the biofouling only (0.38% BW day−1; 66.3±4.9%). The growth of lobsters fed the dry formulated diet in the prototype sea-cage was better than in previous tank growth studies using experimental diets and was probably attributable to animals feeding on biofouling of the sea-cages. Digestive gland histology supported the growth trends, with lobsters fed fresh mussel and the dry formulated diet being in best nutritional condition at the end of the growth experiment. The results indicate that sea-cage culture of juvenile spiny lobsters can provide significant growth advantages over tank systems possibly due to supplementary nutrition from biofouling. However, sea-cage structural design, feeding and diet type are important factors influencing the performance of J. edwardsii juveniles in sea-cages.