Diet immersion time: effects on growth, survival and feeding behaviour of juvenile southern rock lobster, Jasus edwardsii

The effect of water immersion time of a formulated shrimp diet on growth, survival, food conversion and carapace colour of juvenile southern rock lobster, Jasus edwardsii, was determined during a 16 week growth trial. Lobsters were fed one of five diets: pre-soaked shrimp diet (0.5, 2, 4 and 8 h) or non-soaked shrimp diet (0 h). Despite a significant loss in dry matter, protein, ash and astaxanthin from the diet as a result of pre-soaking, there was no effect on the growth, survival, food conversion or carapace colour of lobsters. Feeding behaviour of juvenile J. edwardsii was assessed using glycine, taurine and betaine, previously identified as strong chemoattractants to other crustaceans. Quantification of the antennular grooming frequency (AGF) was identified as the best method of assessing chemoattractant detection in J. edwardsii. The highest rate of AGF was observed in response to glycine at concentrations of 10-4 to 10-6 mol l-1. AGF was subsequently used to assess the excitatory capacity of shrimp diet extract and fresh mussel (Mytilus edulis) extract. Two separate experiments were performed to determine the influence of water immersion on the excitatory capacity (ability to detect the source-(AGF)) and the attractability (capacity to attract to the source-(foraging preference)) of the shrimp diet in comparison to that of fresh mussel flesh. The excitatory capacity of the non-soaked shrimp diet, soaked shrimp diet and fresh mussel extracts were similar. However, the attractability of the non-soaked shrimp diet was greater than soaked shrimp diet and mussel flesh. Lobsters are capable of detecting the shrimp diet regardless of prolonged exposure to water; however, they will selectively move towards a "flesh" rather than a "stale" diet. The results of this study show that the loss of chemoattractants and nutrients from a shrimp diet, caused by leaching, had little impact on the culture performance of J. edwardsii. Thus, even though some lobsters have a slow feeding response and may not feed for several hours after being fed, the dispensation of feed only once per day will not impact on culture performance. However, the influence of leaching on the performance of diets specifically developed for J. edwardsii will need to be re-assessed. © 2003 Elsevier Science B.V. All rights reserved.