Behavioural and morphological aspects of feed intake in spiny lobsters Panulirus ornatus and Sagmariasus verreauxi

The unique characteristics of spiny lobster behaviour and morphology impact feed intake and are crucial factors influencing growth, survival, and feeding efficiency in culture. This thesis explores key aspects of juvenile spiny lobster nutritional behaviour and morphology by investigating culture type, mouthparts morphology, feed characteristics and feeding frequency in context of growth, survival and feeding efficiency in culture. This improved understanding of lobster nutritional physiology will aid in the development of economical and effective formulated feeds and feeding strategies for lobster aquaculture. Furthermore, the holistic understanding of feed intake and behaviour will aid in the development of improved commercial production systems, which remain a significant bottleneck for lobster aquaculture. The two spiny lobster species, Panulirus ornatus and Sagmariasus verreauxi, examined in this thesis, are promising candidates for spiny lobster aquaculture. This thesis includes an investigation of culture type effect on growth, survival and behaviour in early juvenile P. ornatus. The three culture types examined segregated or allowed particular conspecific interactions and included isolated, separated and communal culture. In the isolated culture (individual vessels), lobsters were deprived of all conspecific interactions; separated culture (adjacent cages) eliminated physical interactions, and communal culture allowed all sensory and physical interactions. The influence of chemical cues intensity on growth and survival was also investigated, with two water exchange rates. The feeding behaviour and feed preferences for either mussel gonad, commercial prawn feed or moist feed were investigated using time-series photography. The study showed that physical interactions between conspecifics are essential for optimal culture performance. The communally cultured lobsters exhibited improved growth and moulting frequency. These results may be related to the complex social structures of this gregarious species. Behavioural observations revealed circadian rhythm of interactions with feeds, feed preferences and intake. Observations also revealed differences in lobster behaviour in the differing culture types. Lobsters reared in separation displayed a higher level of interactions with feeds; however, this was not associated with higher feed intake. The study also demonstrated an increase of daylight activity (interactions with feeds and feed intake) with ontogeny from juvenile instar 2 to 4. The focal point in advancing the aquaculture of spiny lobster species is the development of formulated feeds. This thesis includes an investigation of the functional morphology of two spiny lobsters, P. ornatus and S. verreauxi, by analysing the mouthpart morphology and mouth aperture. The analysis is focussed on determining likely feed preference based on morphology to provide knowledge to use in the development of formulated feed. Mouth aperture correlates with lobster carapace length (CL) and is equal to approximately 4 and 7.5% for S. verreauxi and P. ornatus lobsters, respectively. This finding provides a species-specific tool that could be used in experimental studies to define optimal dimensions of pellets, and later inform routine adjustments of formulated feed pellet size optimal to the size of the lobster. Differences in mouthpart morphology through ontogeny included an increase of calcification and robustness, which likely reflects a different requirement in the texture (softness/hardness) of the pellet as the animals develop. Spines and setation are a prominent feature of the mouthpart morphology and differ between species and during ontogeny. Spines on maxillipeds III and II and crista dentata on maxillipeds III are likely to play an important role in holding and manipulation of feed before ingestion. Hence, pellet texture will probably need to accommodate spinal puncturing and grasping in a species and age specific manner. Ontogenetic changes in setation were found, with much richer setation proportionally to the size of mouthpart present in first instar juvenile lobsters as well as species-specific differences. This indicates shifts in functions of particular mouthparts at different life stages which likely implies differences in filter feeding with age and between species. This is unlikely to be of high importance in pellet feeding development but could represent an avenue of investigation for the difficult first feeding juvenile stage. Collectively, the differences during ontogeny and between species suggest that formulated feeds may need to tailor to species and life stage, particularly regarding pellet dimensions and texture. Morphological investigations allowed for the establishment of biologically coupled feed pellet diameters in two experiments which examined the amount of feed waste produced by S. verreauxi juveniles in relation to pellet diameter, length and texture. The study examined the relationship between feed waste composition and feeding efficiency by juvenile spiny lobster, S. verreauxi. Lobsters were fed seven different pellet diameters in each of two tested textures (hard and dry, HDP; soft and moist, SMP) or seven pellet lengths (HDP only), in two separate experiments. After feeding lobsters at 0.5% BW for 6 h, feed waste was collected and categorised as either feeding related waste (FRW), which was resulting from manipulation and maceration or non-feeding related waste (NFRW), which was uneaten/unmanipulated feed. In all tested feeds, particularly HDP, increasing pellet diameter or length corresponded in an increase of FRW and decrease of NFRW resulting in no difference in total feed waste in any treatment investigated. Thus, even if there was a clear improvement in feeding efficiency with small feed dimensions (i.e. low FRW), feed intake was not improved. Feed leaching rate decreased with pellet size indicating more rapid decline in feed attractiveness for smaller pellets. The findings indicate a counteractive interaction exists between pellet size and feed attractiveness and suggests that improved sustained feed attractiveness would further enhance feeding on small pellets. Future research should aim at optimising feed dimensions simultaneously to support efficient feeding whilst enhancing prolonged attraction/gustatory stimulation. The sensory stimuli including olfactory, visual, acoustic and tactile, are important aspects of feed exposure and the optimisation of feeding schedules. Feed attractiveness and availability are key drivers for maximising feed intake by juvenile lobsters. These aspects were investigated in a study focussed on the effect of feed frequency on survival, growth and behaviour of early-stage (instars 2-6) juvenile P. ornatus. The lobsters were exposed to one of six feeding frequencies with either one, two, four, eight, sixteen and thirty-two feed supplies per day with overall daily ration the same between treatments. The study showed that increasing feed frequency from one to around a maximum of sixteen feeds per day, improved lobster growth by increasing feed intake. Growth and feed intake maximisation at 16 feeds per day is thought to be due to optimization of feed attractiveness relative to the rapid rate of attractant leakage with immersion. Over and above sixteen feeds per day, feed intake and growth decreased which is thought to be associated with saturation of the culture environment with attractants and reduced the behavioural response to feed supplies. Increased growth at sixteen feed frequency corresponded with higher moulting events and consequently heightened cannibalism. While circadian rhythm indicated more activity at night, there was no interaction with feed frequency. Our results indicate that a feed frequency of sixteen per day was around optimality to maximise growth for P. ornatus early juveniles but cannibalism at moulting is a serious problem which has to be addressed for successful intensive aquaculture of this species. Collectively, this thesis exposed the behavioural and morphological complexity of juvenile spiny lobsters in context of commercial production systems and formulated feed intake. Findings include the importance of gregariousness and physical interactions for growth, and a convoluted interaction between feed intake, growth rate and cannibalism. This thesis highlights the importance of further work to better understand and resolve the apparent negative consequence of growth (cannibalism) for the development of spiny lobster aquaculture. The morphological investigation relating to pellet dimensions showed that the feed shape should be adapted to the size of lobster. However, it has to be considered in context of the wide behavioural repertoire, affecting feed intake in spiny lobsters. The importance of feed attractiveness and availability highlights importance of even subtle improvements to chemosensory and visual exposure of feeds.