Feed availability and its relationship to survival, growth, dominance and the agonistic behaviour of the southern rock lobster, Jasus edwardsii in captivity

The effect of feed availability (ration level and feeding frequency) on the culture performance of the juvenile (5-22 g) southern rock lobster Jasus edwardsii was examined to determine whether multiple daily feeding of a formulated feed would stimulate growth. Furthermore, the relationships between feed availability, agonistic behaviour, dominance, growth and survival were examined. A total of 252 lobsters (mean weight 5.26 g) were stocked into 28 black 52-1 tanks at a density of nine lobsters per tank (42 m(-2)) and maintained at a temperature of 18.8 degreesC in a recirculating seawater system for 119 days. Lobsters were fed with high (4% BW day(-1)) or low (0.5% BW day(-1)) rations divided between one, two or four meals per day. These regimes were compared to a regime of fresh mussels (Mytilus edulis) fed to excess once per day. Feeding lobsters with a high-ration level, 4 day(-1), made no significant (P>0.05) improvements in specific growth rate (SGR) (0.77-0.82% BW day(-1)), survival (75-84%) or biomass yields (96-102 g) compared to feeding 1 or 2 day(-1). Low-ration-fed lobsters had a higher final mean weight (17.5-20.9 g) compared to high-ration lobsters (13.4-14.3 g), however, survival of lobsters that were fed with low ration of 4 day(-1) (41%) was significantly (P < 0.05) lower than that of high-ration-fed lobsters (75-84%). The larger final mean weight of lobsters, fed with a low ration, was explained by the increased nutrient uptake from cannibalism. Significantly (P < 0.05) higher biomass yields were achieved by lobsters fed with fresh mussels once per day which was achieved through the combined effects of larger final mean weight (17.1 g) and improved survival (91%). Lobsters were size-ranked (g) to determine the effects of feed competition on the growth and survival of individuals of different rank. The ability and/or motivation of the largest lobsters to maintain their size status increased as feed availability decreased, suggesting that feed restrictions increased the strength of dominance. Size-ranking also demonstrated that small lobsters were more vulnerable to being cannibalised, especially when the feed-ration level was low. Feed competition was consistent with the concept of economic defensibility, predicting that levels of agonistic behaviour are highest when a low ration was patterned into smaller, more easily defended meals (low-ration fed, 4 day(-1)). In contrast, feed competition and agonistic behaviour were rarely observed when feed was freely available (high-ration fed, 4 day(-1)). The high levels of cannibalism of small size-ranked lobsters meant that assessing growth depensation was not a useful approach to the evaluation of the relationships between competition and growth in groups. The implications for J. edwardsii culture are that feeding high-ration levels of formulated feeds, more than once daily, reduces feed competition and incidence of agonistic behaviour. However, there appear to have few benefits in terms of growth or survival. The recommendation from this study is to feed lobsters once daily to excess after dusk. (C) 2003 Elsevier Science B.V. All rights reserved.