Effects of diet on the growth, survival, and condition of sea-caged adult southern rock lobster, Jasus edwardsii

Live-holding of fisheries-caught adult southern rock lobster (Jasus edwardsii) presents a means of value-adding to the South Australian commercial catch through strategic marketing and product enhancement. This study investigated the effects of live mussel and three manufactured diets on the survival, growth, and condition of sea-caged adult J. edwardsii held for an extended period of 29-30 weeks during the closed fishing season. Two trials were conducted in existing industry cage systems. All four diets tested were successful in keeping lobsters alive, promoting growth at moult, and maintaining/improving the condition of lobsters. Unfed lobsters had lowered survival, negative or zero growth at moult, and lowered condition. All lobsters moulted during the trials. Addition of 1% mussel mince to pellets as a feeding stimulant did not increase survival or growth. Males showed substantially greater weight gain at moult than females (means of 8% for females and 17% for males). Biomass of male lobsters increased by up to 16% in one trial treatment, where growth of individual lobsters more than compensated for weight loss caused by mortality. Two different levels of carotenoid (0.15% and 0.25%) proved sufficient to maintain and/or improve colour. Where females were held separate from, but adjacent to, males there was some spawning activity (up to 14%). The one negative outcome of the study was that tail fan damage was found to be a major problem, occurring in both trials and across all diets without apparent pattern. The causes and management of tail fan damage need to be addressed before a long-term live-holding industry can be developed. However, in terms of survival and weight gain, results were very encouraging as improvements in pellet formulation, pellet production, and food delivery can be expected.