Cannibalism is a limiting factor in the culture of the commercially valuable tropical rock lobster, Panulirus ornatus. Cannibalism is most common during the early juvenile stage when P. ornatus undergoes frequent moulting of the exoskeleton. Moulting is required to facilitate growth, however the process does expose the soft-bodied post-moult lobster to cannibalism. Despite the importance and impact of this behaviour, few studies have directly examined cannibalism of lobsters in culture.
This study quantifies the contribution of cannibalism to juvenile mortality and investigates pathways responsible for mediating this behaviour. A total 900 hours of time-lapse footage was recorded over 30 days, identifying and characterising moulting and cannibalism events. A 50% mortality rate was identified and attributed solely to the cannibalism of live, moulting lobsters. Over 20% of individual moulting events resulted in cannibalism of the moulting lobster. There was an increase in locomotor activity observed for up to one hour prior to cannibalism, demonstrating the pervasiveness and predetermination of this behaviour. To understand the mechanisms driving cannibalism and reduce its prevalence we investigated the role of chemoreception, particularly olfaction, in the detection of conspecific moulting cues. A behavioural assay was established using a two-current choice flume, demonstrating that lobsters display distinct preferences for moulting cues based on their moult stage and their relationship to the moulting lobster. When the olfactory organ of lobsters is functionally ablated, they no longer demonstrate preference behaviour to conspecific moulting cues in this assay, indicating olfaction is a key link in cannibal-prey recognition. Transcriptomic analysis of the olfactory organ identified several olfactory ionotropic receptor isoforms, adding to the growing genomic and transcriptomic knowledge for this key aquaculture species. These findings demonstrate the importance of conspecific chemical cues and olfaction in facilitating a behavioural response to a moulting lobster.