Lobster Diet Research Articles

Lobster predation on barren-forming sea urchins is more prevalent in habitats where small urchins are common: a multi-method diet analysis

Context In Tasmania, Australia, the government’s response to range-extending, barren-forming longspined sea urchin (Centrostephanus rodgersii) includes rebuilding of southern rock lobster (Jasus edwardsii) stocks to increase predation. But lobster preference for native species and continued barren expansion challenges the control efficacy. Aims To determine the impact of lobster predation on C. rodgersii in different habitats. Methods Multi-method dietary analysis consisting of stomach contents, faecal DNA and stable isotopes was performed on 64 lobsters from four habitats varying in barren extent and density of urchins and lobsters. Key results C. rodgersii contributed to lobster diet in all barren habitats and was found in lobsters of every size class. Stable isotope and DNA analyses showed that C. rodgersii was more common in lobster diet than were targeted native species at incipient barren sites. Surprisingly, in extensive barrens C. rodgersii is less prominent in lobster diet. Conclusions Combined with site-specific urchin population data, our findings indicated that lobster predation may be less effective at sites where most C. rodgersii individuals have reached a size refuge than at sites dominated by small urchins. Implications Lobster predation may provide a useful control for smaller C. rodgersii, but top–down predatory control may be constrained at sites dominated by urchins that exceed the size suitable for lobster predation.

Trophic discrimination factors and stable isotope variability in a captive feeding trial of the southern rock lobster Jasus edwardsii () (Decapoda: Palinuridae) in Tasmania, Australia

Abstract Trophic discrimination or fractionation factors (TDFs), such as ∆15N and ∆13C, are used in stable isotope mixing models to account for differences between source tissues (diet/prey) and consumer tissues (predator). We aimed firstly to obtain TDF values for a spiny lobster, the southern rock lobster Jasus edwardsii (Hutton, 1875), to better understand lobster diet in the wild and secondly to investigate variability in isotope signature within tissues of individuals and across a temporal scale to test if non-lethal sampling can be used in an ecological context. We conducted an 18-mo captive feeding trial with juvenile lobsters using three diet treatments and analysed dorsal and leg muscle, along with dorsal and leg exoskeleton for δ13C and δ15N values. Average TDFs for the three diet treatments were 3.86 ± 0.98‰ (∆13C) and 5.06 ± 0.65‰ (∆15N) for leg muscle, and 4.45 ± 1.04‰ (∆13C) and 4.36 ± 0.6‰ (∆15N) for dorsal muscle. When tested against wild lobsters and prey, these TDFs outperformed multi-taxa TDFs found in the literature. Isotope values from lobster leg muscle were not identical to associated dorsal muscle but the two were highly correlated, indicating that non-lethal sampling is acceptable. Values for exoskeleton isotope were significantly different from muscle, likely due to the exoskeleton not being in a constant state of growth and replacement, unlike the muscle tissue, which constantly incorporates new material. We conclude that our experimentally derived TDFs are suitable for mixing model analysis for J. edwardsii and when tested on a wild sample of lobsters they outperformed other TDFs reported in the literature. We show that non-lethal sampling using leg muscle is an appropriate sampling method, since this tissue is highly correlated to the commonly used dorsal muscle. This option for non-lethal sampling enhances the potential to widely sample wild populations or sample during industrial processing without the need to sacrifice whole animals.

Contribution of mussel fall-off from aquaculture to wild lobster Homarus americanus diets

Anthropogenic subsidies to natural systems can influence the diet of mobile omnivore species and co-occurring species. This study assessed if fall-off from mussel aquaculture subsidized wild populations of mobile scavengers and predators, such as the commercially important lobster Homarus americanus. A Bayesian stable isotope-mixing model with parameters determined from the literature and from a 105 days laboratory feeding experiment was applied to wild lobsters to determine how important the various food sources were in these lobsters, especially mussel fall-off. Isotopic values were mainly affected by lobster size with model outputs indicating that large lobsters (>80 mm cephalothorax) fed mainly on mussels from the mussel farm (46% of the diet) while small ones fed mostly on the rock crab Cancer irroratus (99%). The contribution of mussel subsidies to the lobster's diet was thus size-specific and direct (i.e. through mussel fall-off and not through co-occurring species such as rock crab). The absence of a link between food sources and lipid energy content in lobsters suggested that the reduction of rock crab consumption would have to be more drastic to affect the general health of large lobsters in the short term.

Diet of the spiny lobster Jasus paulensis from the Tristan da Cunha archipelago: Comparisons between islands, depths and lobster sizes

Diet of the Tristan spiny lobster Jasus paulensis was examined using gut content and Stable Isotope Analyses (SIA) to assess whether diets differed among three islands in the Tristan da Cunha archipelago (Inaccessible, Nightingale and Tristan islands), and between small and large lobsters at two depth intervals. Gut fullness was significantly less at Nightingale Island, suggesting overall less food there. Diet differed significantly among all islands, depths and sizes, although multidimensional scaling (MDS) and constrained canonical analysis of principle coordinates (CAP) plots showed considerable overlap and variability in diet. Lobster diet from Tristan Island showed a greater within-island similarity and was significantly less diverse, suggesting a more impoverished reef and narrower feeding niche, while dietary differences between size and depth reflected prey availability. Carbon and nitrogen stable isotope signatures differed among the islands, and carbon signatures between depths. Jasus paulensis appeared to be an opportunistic omnivore, with diet reflecting impoverished reef habitats. In addition, our data showed no evidence of soya remnants in the gut contents or tissue signatures of lobsters at Nightingale Island, following a soya spill there four years previously. However, gut fullness was less at Nightingale. This may have increased the attractiveness of baited traps, possibly explaining an observed rise in CPUE after the spill.

Effect of dietary lipid source on expression of lipid metabolism genes and tissue lipid profile in juvenile spiny lobster Sagmariasus verreauxi

The spiny lobster Sagmariasus verreauxi is an emerging lobster species for intensive aquaculture. The lack of any nutritional information required for feed development in this species initiated this study to understand the effect of different dietary lipid sources on tissue lipid profiles and expression of selected lipid metabolising genes. Krill oil, marine oil (blend of fish oils), and vegetable oil (combination of linseed and palm oil), were utilised to formulate three experimental feeds with different phospholipid, triacylglycerol and polyunsaturated fatty acid profiles. Experimental feeds were administered to freshly moulted juvenile S. verreauxi for 50 to 55days, to determine the effect of lipid sources on the nutritional status, fatty acid composition and expression of genes related to fatty acid biosynthesis, β-oxidation, lipid catabolism and regulation of lipid metabolism. While there were no significant differences in terms of weight gain and mortality among different dietary treatments, the fatty acids composition in the hepatopancreas and to some extent, muscle tissues correlated with the fatty acids composition of the respective dietary treatments. Vegetable oil diet resulted in higher expression of genes related to β-oxidation, which indicates selectivity towards utilisation of monounsaturated fatty acids for energy in this species. In tandem, genes related to fatty acid and cholesterol biosynthesis were upregulated, suggesting their importance in the marine lobster diet. This is the first report on the use of formulated feeds to successfully maintain juvenile S. verreauxi.

Caribbean Spiny Lobster Fishery Is Underpinned by Trophic Subsidies from Chemosynthetic Primary Production

The Caribbean spiny lobster, Panulirus argus, is one of the most valuable fisheries commodities in the Central American region, directly employing 50,000 people and generating >US$450 million per year [1]. This industry is particularly important to small island states such as The Bahamas, which exports more lobster than any other country in the region [1]. Several factors contribute to this disproportionally high productivity, principally the extensive shallow-water banks covered in seagrass meadows [2], where fishermen deploy artificial shelters for the lobsters tosupplement scarce reef habitat [3]. The surrounding seabed communities are dominated by lucinid bivalve mollusks that live among the seagrass root system [4, 5]. These clams host chemoautotrophic bacterial symbionts in their gills that synthesize organic matter using reduced sulfur compounds, providing nutrition to their hosts [6]. Recent studies have highlighted the important role of the lucinid clam symbiosis in maintaining the health and productivity of seagrass ecosystems [7, 8], but their biomass also represents a potentially abundant, but as yet unquantified, food source to benthic predators [9]. Here we undertake the first analysis of Caribbean spiny lobster diet using a stable isotope approach (carbon, nitrogen, and sulfur) and show that a significant portion of their food (∼20% on average) is obtained from chemosynthetic primary production in the form of lucinid clams. This nutritional pathway was previously unrecognized in the spiny lobster's diet, and these results are the first empirical evidence that chemosynthetic primary production contributes to the productivity of commercial fisheries stocks.

An exception to the rule: top-down control of a coral reef macroinvertebrate community by a tropical spiny lobster

In temperate habitats, predation by lobsters creates trophic cascades that reverberate through benthic communities. However, the influence of lobsters on tropical benthic communities is thought to be minimal due to higher prey diversity and the mobility and broad diet of lobsters. We hypothesized that this would not be the case for the spotted spiny lobster (Panulirus guttatus Latreille, 1804), an obligate, philopatric dweller of Caribbean coral reefs. Our study took place in the Florida Keys (USA), where we examined the gut contents of wild lobsters, conducted laboratory experiments on lobster prey selection and foraging effectiveness in rubble, and manipulated lobster density on isolated patch reefs to examine the effects of lobster predation on macroinvertebrate prey over a 3-yr period. We found P. guttatus to be a generalist carnivore that consumed a suite of macroinvertebrates, including important reef herbivores (e.g., herbivorous crabs, gastropods, and urchins) that comprised >60% of its diet. Higher densities of P. guttatus exerted strong top-down control over the abundance and composition of macroinvertebrate prey in rubble substrates on patch reefs, but not prey living in substrates dominated by macroalgae. Lobster foraging success in rubble also depended on rubble size; lobsters extracted prey from and overturned rubble more easily when rubble was smaller. The abundance and high site fidelity of predatory P. guttatus appears to provide the necessary conditions for top-down control of prey in coral reef rubble zones, an effect similar to the powerful influence of lobster predation observed in temperate ecosystems.

Characteristics of faecal and dissolved nitrogen production from tropical spiny lobster, Panulirus ornatus

Spiny lobster aquaculture in sea-cages produces both particulate (faeces and waste feed) and soluble wastes [dissolved inorganic nitrogen (DIN)] that have the potential to degrade the environment. To begin to understand the environmental impacts of tropical spiny lobster aquaculture, the waste products of these lobsters were quantified, including the settling velocity of faecal material and DIN output from lobsters of a range of sizes and fed two dietary treatments (seafood and artificial diet), as well as determining the nitrogen leaching from faeces and diets for lobsters. The mean faeces settling velocity of lobsters fed with seafood was significantly higher than those from lobsters fed with artificial diet (0.30 ± 0.01 and 0.22 ± 0.01 cm s−1, respectively, mean ± SE), but the settling velocity of faeces did not differ among the lobsters of different sizes for each diet. The settling velocity of faecal material showed a positive relationship with faeces weight, volume and density but not length. Both carbon and nitrogen content in faeces showed no significant differences between the two diets. Feeding activity doubled the DIN output from lobsters consistently for both dietary treatments compared with unfed lobsters. Nutrient leaching from samples of faeces and diet was highly variable and did not differ among lobsters of different sizes or between the two dietary treatments. Overall, while faecal material, waste feed, as well as DIN excretion by lobsters in aquaculture operations could potentially negatively impact the environment, their faeces settling velocity and DIN output is markedly lower than fin-fish. Thus, the environmental impact from lobster aquaculture is unlikely to be as intensive as for fin-fish aquaculture.

Modelling carbon deposition and dissolved nitrogen discharge from sea cage aquaculture of tropical spiny lobster

Abstract The tropical spiny lobster, Panulirus ornatus, is farmed in floating sea cages situated in shallow coastal waters in many parts of the Asia-Pacific region. Despite the rapid expansion of this aquaculture activity, very little is known about its environmental impacts. This study combines computer modelling with previous laboratory measures to provide information on benthic carbon deposition and the production of dissolved inorganic nitrogen (DIN) from hypothetical sea cage aquaculture of spiny lobsters. Modelling scenarios were run with two different lobster aquaculture stocking densities (3 and 5 kg m−3) and various feed conversion ratios (FCRs) using natural seafood or artificial lobster diet (FCR 1.28–28). Simulations from the model showed that cumulative benthic carbon deposition varied from 0.1 to over 0.8 kg C m−2 year−1, while the mean DIN levels around sea cages ranged from 5.6 up to 25 µg N l−1 and the maximum DIN levels ranged from 10.8 to 165 µg N l−1. The results showed that feeding lobsters with seafood resulted in a markedly higher benthic carbon loading and release of DIN when compared with artificial lobster feed. Therefore, the elimination of the use of trash fish would greatly reduce the environmental impacts of spiny lobster aquaculture. Overall, the effects from spiny lobster aquaculture were spatially localized with the highest concentrations of carbon deposition and DIN directly beneath the sea cages. Therefore, it seems unlikely that spiny lobster aquaculture in sea cages will cause adverse environmental effects unless the lobsters are heavily stocked and supplied with poor quality feed.

Palinurid lobster aquaculture: nutritional progress and considerations for successful larval rearing

AbstractThe closed‐cycle rearing of palinurid lobsters in commercially relevant quantities currently represents one of the most difficult challenges facing modern‐day aquaculture. The length and complexity of the larval life cycle exacerbate the problem, comprising the major bottleneck to their successful aquaculture. The general consensus is that developments in the key research area of nutrition will provide the necessary breakthroughs to make the closed‐cycle rearing of lobster a reality. Due to the cryptic nature of feeding preferences and complex larval morphology, a commercially formulated feed for their culture does currently not exist. Nevertheless, there has been a wealth of research conducted to elucidate many of the unknowns concerning larval nutritional requirements. This review presents a synthesis of this information, ranging from investigations of larval morphology and feeding behaviour, hatchery nutrition practices, the elucidation of wild prey items and the nutritional content of wild‐caught larval species. Based on the information available, this review culminates with a ‘best guess’ formulation for a larval spiny lobster diet, taking aspects concerning both the physical and chemical attributes of formulation into consideration. It is concluded that larval spiny lobsters are likely comparatively low in relation to other larval species with respect to their quantitative dietary requirements. Ultimately, the overall success of the larval cycle appears to be dictated by the stockpiling of lipids to fuel an energy‐demanding metamorphosis and a subsequent nonfeeding puerulus phase. These insights provide valuable direction for the formulation of nutritionally complete feeds to permit the closed‐loop culture of spiny lobster species.

Individual variability in trophic position and diet of a marine omnivore is linked to kelp bed habitat

Omnivores play an important role in the routing and distribution of organic matter across food webs. We demonstrate a novel approach to quantifying the coincidence of landscape- scale nutritional gradients with niche breadth in terms of variability in trophic level and use of basal organic matter sources. We provide an example of the links between individual variability in resource use and habitat of a broad-spectrum omnivore, the red rock lobster Jasus edwardsii. Information on the co-occurrence of J. edwardsii with kelp bed habitats Ecklonia radiata and with their preferred prey Mytilus edulis galloprovinciallis were collected at 60 sites across Fiordland, southwest New Zealand. Analysis of distance-based linear models (DISTLM) indicated that the presence of mussels was the best predictor of lobster occurrence in the model set. At a subset of sites, we collected lobster muscle for stable isotope analysis and measured 3 demographic para- meters from the lobsters: relative abundance, sex and carapace lengths. We characterised habitats with surveys of common kelp and mussels. Using stable isotope signatures (δ 13 C and δ 15 N), we calculated individual-based estimates of trophic level and the mixture of organic matter sources, i.e. phytoplankton and macroalgae. Using DISTLM, lobster and mussel densities best explained variability in lobster diet. Variability in resource use was distinct inside and outside of kelp bed habitat. In kelp beds, lobsters fed at a higher average trophic level, with low variability among individuals in trophic level and use of organic matter sources. Outside kelp beds, individual vari- ability indicated broad trophic diversification. These patterns indicate a strong influence of the nutritional landscape at the scale of the metapopulation, which has important implications for understanding dietary influences on population structure.

Purple sea urchins Strongylocentrotus purpuratus reduce grazing rates in response to risk cues from the spiny lobster Panulirus interruptus

The classical view of trophic cascades is that predators, by consuming herbivores, exert a positive indirect effect on plants. Although this form of trophic cascade has been demonstrated in a variety of terrestrial, aquatic, and marine systems, growing evidence suggests many trophic cascades are driven by anti-predator behaviors in prey. Despite abundant evidence of behavioral responses by sea urchins to predators, there has been little examination of how predation risk may influence urchin grazing rates. To determine if purple sea urchins Strongylocentrotus purpuratus graze less in the presence of predation risk, I monitored individual urchin grazing on the kelp Macrocystis pyrifera in the presence and absence of waterborne cues from damaged conspecifics and the predatory spiny lobster Panulirus interruptus. Sea urchin grazing rates were similar in the presence and absence of damaged conspecifics, but sea urchins exposed to lobster cues, regardless of lobster diet, reduced grazing rates by 44%. Given that trophic cascades involving herbivorous sea urchins exert an impor- tant influence on primary production in kelp forests, these results suggest that predation risk may play an important but under-appreciated role in the dynamics of kelp forest food webs and primary production.

Trophic effects of fishing southern rock lobster Jasus edwardsii shown by combined fatty acid and stable isotope analyses

The southern rock lobster Jasus edwardsii is a commercial species that has benefited from the complete protection offered by no-take reserves, with higher abundances and larger ani- mals recorded in reserves than in adjacent fished areas. What remains unclear is whether there is any change in the diet of lobsters in reserves, for example, as a result of increased intraspecific competi- tion for food. We used combined chemical tracers to examine the diet of lobsters in fished and reserve areas in 2 bioregions in eastern Tasmania. δ15N values of lobsters were richer in fished than in reserve areas, indicating that lobsters eat a greater proportion of food items from higher trophic levels in fished areas. Mixing models suggest that ascidians, sea urchins and the turbinid gastropod were all important food sources for lobsters, but the importance of these food items differed between biore- gions. This spatial variability may suggest thatthe small size of the reserve in one bioregion is inad- equate at ensuring the diet of lobsters is protected from fishing pressure. Fatty acid profiles of lobsters supported the importance of these food sources to lobsters. Differences between bioregions, or inside and outside of reserves, were not apparent using fatty acids. The present study highlights that lobster fishing has the capacity to alter the trophic status of prey for generalist predators and suggests that fatty acid analyses may be limited in detecting changes in the dietary composition of such generalist feeders.

Digestive enzyme response to natural and formulated diets in cultured juvenile spiny lobster, Jasus edwardsii

A better understanding of the nutritional requirements and digestive processes are essential for improving the consumption and growth of spiny lobsters on formulated diets used in commercial culture. Differences in the enzymatic digestive response (i.e., post-prandial changes in digestive enzyme activity, digestive fluid pH and digestive gland structure) of juvenile Jasus edwardsii fed either a natural (mussel flesh) or a formulated diet were investigated. Digestive enzyme activities (total protease, trypsin, α-amylase and α-glucosidase) and soluble protein concentration in the foregut after a single feeding event for the two dietary treatments displayed a common peak at 4 h, and a second peak at 18 h post-prandial for the mussel fed lobsters only. In lobsters fed the formulated diet, the lumen size of the digestive gland tubules was 88% larger, the number of B-cells per tubule at 18 h post-feeding was 269% higher, and the pH of the digestive gland was lower (6.20 versus 6.34) than in lobsters fed mussel flesh. These results indicated an intensified intracellular digestion in the digestive gland on the formulated diet that could have played a role in the poor appetite revival (>18 h) exhibited on this diet. Rearing of juvenile lobsters on the formulated diet for 6 months resulted in a marked decrease in the digestive capacity (i.e., total and specific enzyme activity of the foregut and digestive gland) and nutritional condition of lobsters. Overall, these results suggest that difficulty in the digestive processing of formulated feeds may help to explain the bottlenecks encountered in developing more effective formulated diets for juvenile spiny lobster culture. Improvements in the dissolution of dietary ingredients upon entering the foregut, and in the digestibility of dietary carbohydrate sources, may assist in further improving the performance of formulated diets for lobsters.

Contribution of bait to lobster production in an oligotrophic marine ecosystem as determined using a mass balance model

The fishery for the western rock lobster ( Panulirus cygnus) in Western Australia is Australia's largest trap-based fishery, deploying 8.8 million pot lifts, landing on average 11,000 tonnes of lobster and using approximately 14,000 tonnes of bait annually. A mass balance model was constructed to determine the potential contribution of this bait to the diet of western rock lobsters. Bait is potentially a significant subsidy given the oligotrophic nature of Western Australia's marine environment. The mass balance model was constructed on the principle that the biomass of the lobster population reflects the difference between inputs (growth, immigration) and outputs (natural and fishing mortality and emigration). Biomass calculated using this approach was within 7% of biomass calculated from independent estimates based on depletion analysis, indicating the model is robust. The food required to explain observed growth was then calculated, allowing the potential contribution of bait to lobster diet to be assessed. The abundance of natural diet items on the benthos was sufficient to explain the observed growth of lobsters, with bait contributing a maximum of 13% of lobster food requirements over the whole ecosystem. This contribution of bait will differ spatially and temporally reflecting uneven distribution of fishing effort and may be as high as 35% during some months of the fishing season, a result consistent with dietary studies based on stable isotopes. Given observed effects of organic matter addition on ecosystem processes as observed in trawl fisheries and aquaculture operations, it is likely that the effects of bait addition on ecosystem function are more widespread than lobster production.

Western rock lobsters ( Panulirus cygnus) in Western Australian deep coastal ecosystems (35–60 m) are more carnivorous than those in shallow coastal ecosystems

The western rock lobster ( Panurilus cygnus George.) is a conspicuous consumer in the coastal ecosystems of temperate Western Australia. We used stable isotope analysis and gut content analysis to determine the diet and trophic position of western rock lobsters from mid-shelf coastal ecosystems (35–60 m depth) at three locations. Lobsters were primarily carnivorous, and no consistent differences in diet were detected with varying lobster size, sex or among locations. The main components of the diet were bait (from the fishery) and small crustaceans – crabs and amphipods/isopods. Foliose red algae, bivalves/gastropods and sponges were minor contributors to diet. The diet of lobsters in deep coastal ecosystems differed from the results of previous studies of diets of lobsters from shallow coastal ecosystems. In particular, coralline algae and molluscs – important prey in studies of lobsters from shallow coastal ecosystems – were minor components of the diet. These differences are likely to reflect differences in food availability between these systems and potentially, differences in choice of prey by lobsters that inhabit deeper water. Given the high contribution of bait to lobster diet, bait is likely to be subsidizing lobster production in deep coastal ecosystems during the fishing season.

Variation in evacuation rates of different foods skew estimates of diet in the western rock lobster Panulirus cygnus

Knowledge regarding differences in evacuation rates of diet items from a consumer’s stomach is important when using gut content analysis to quantify consumer diet. Evacuation rates of three diet items (pilchards, crabs and coralline algae) from the foreguts of western rock lobsters (Panulirus cygnus) were compared in aquaria. To determine evacuation rates, lobsters were allowed to consume offered food over a 90-min feeding period before being killed at 4, 6, 8, 10 and 12 h after the feeding period concluded. Diet items differed in their rate of evacuation from lobster foreguts with coralline algae evacuated most rapidly, followed by crabs, then pilchards. The evacuation of crabs and pilchards was still not complete 12 h after the feeding period concluded. Food not evacuated after 12 h predominantly consisted of hard components of the lobster diet, indicating that it is these components that account for slower evacuation. Observed variation in evacuation rates between diet items may skew the results of studies that use gut content analysis to quantify the diet of western rock lobsters.

Use of commercial Artemia replacement diets in culturing larval American lobsters ( Homarus americanus)

This work reports on the successful incorporation of commercial formulated Artemia replacement diets as 50% of a larval American lobster diet. Combination diets of either live Artemia nauplii or frozen adult n-3 fatty acid enriched Artemia with a rotation of three commercial formulated diets resulted in equivalent survival to stage IV (19–25%), postlarval size and subsequent early juvenile performance compared to an Artemia nauplii plus frozen Artemia combination diet. A 100% formulated diet resulted in reduced larval survival (6%) and postlarval size, while a larval diet of 100% frozen adult Artemia resulted in reduced postlarval quality and early juvenile performance. The much lower price of the formulated diets compared to the prices of Artemia nauplii and frozen Artemia makes its inclusion in the lobster larval diet the most cost-effective diet choice.

The importance of rock crab ( Cancer irroratus) for growth, condition and ovary development of adult American lobster ( Homarus americanus)

The rock crab ( Cancer irroratus) fishery is a growing industry in eastern Canada. Considering that American lobster ( Homarus americanus) is highly dependent on the rock crab as a food source, questions have arisen as to the impacts such a fishery would have. This study examines how different rations of rock crab can affect somatic growth, condition and ovary development of mature lobster, following molt. We tested the effect of four diets containing various amounts of rock crab, blue mussel and green sea urchin. The four diets were: a reference diet where 80% of the energy was provided by rock crab (T), a diet with half the crab content of the reference diet but containing as much protein (isoproteinic) as the reference diet (E1), a diet without crab but isoproteinic with the reference diet (E2), and a diet without crab but with as much energy (isocaloric) as the reference diet (E3). In general, lobsters fed a diet without rock crab showed lower glycogen and lipid content and higher water content in the digestive gland. Growth of chela muscles was lower, although diet did not have any effect on protein concentration. Ovary development was stunted in females. Differences were mostly striking in diet E3, which contained less proteins than the reference diet. Results obtained from diet E2 were also significantly different from the reference diet and not from E3, suggesting that mussel and urchin, even if given in a greater amount, are not equivalent to crab and cannot fully compensate the absence of this essential component of the lobster's diet. The importance of rock crab for lobster may be due to its high protein content and presence of particular amino acids. Our results strongly suggest that the development and management of a rock crab fishery should be cautious and governed by a multi-species approach.

Antinutritional properties of egg white in diets for lobsters.

In crustaceans, performance of dietary proteins has been shown to be influenced by a number of factors and is not limited to only amino acid compositions. Egg albumin serves a prominent role as an amino acid standard for terrestrial animals, however it is utilized poorly as a single protein source in lobster diets. This study investigated the influence of processing on egg white suitability in diets for lobsters.Egg white, commercially obtained as well as prepared in the laboratory was used as a protein source in juvenile lobster diets. Sprayed dried egg white, with or without having been heated to 110°C for 20 minutes performed poorly in contrast to casein control diets. Egg white which had first been cooked to coagulation and later dried was significantly better than either the casein control or other egg diets. Findings suggest antinutritional factors, such as trypsin inhibitors, strongly influence the suitabilty of egg white as a protein source of lobsters, however, appropriate denaturation techniques can minimize their effects.