Moult Increment Research Articles

Effect of Dietary Protein to Energy Ratios on Growth, Digestive Enzyme Activity and Body Composition of Captive Juvenile Spiny Lobsters, Panulirus Ornatus (Fabricius, 1798)

Abstract An evaluation of six dietary protein-to-energy (P/E) ratios was conducted to the early juvenile lobsters (Panulirus ornatus) by investigating the ratio effects on physiology, digestive enzyme activities, body composition, and amino acid profiles. Juvenile lobsters (0.25±0.01 g) were individually kept in aquaria and treated with six isoenergetic formulated diets of P/E ratios of 21.8, 22.5, 23.5, 24.6, 25.3 and 26.6 mg KJ–1. After 8 weeks of feeding experiment, the differentiation on dietary P/E ratios was found to have affected the specific growth rates, but not the survival, moult increment, moulting rate, moult interval and average daily moulting rate of juvenile lobsters. The dietary P/E ratio also influenced the protease, lipase, superoxidase dismutase activities, and body composition of juvenile lobster. The increase in dietary protein levels significantly affected the increase of the specific growth rate, while increased dietary lipid levels only affected the length increments. Both protein and lipid content were found in the whole body of the juveniles which reflected the treated dietary composition. Results indicated that a P/E ratio of 26.6 mg KJ–1 (55% dietary protein and 9% dietary lipids) can yield the maximum growth and digestive enzyme activities from among the studied diets.

Post-settlement growth and sexual dimorphism in the size and proportion of the body of the varunid crab Gaetice depressus (De Haan, 1833) (Decapoda: Brachyura: Varunidae) based on laboratory-reared material

Abstract We investigated post-settlement growth patterns and sexual dimorphism in the carapace, pelon, and cheliped dimensions of the varunid crab Gaetice depressus (De Haan, 1833). We reared crabs in the laboratory from hatching through megalopae to the first to tenth instars, and measurements were made of exuviae or specimens of crabs that successively molted. The males were larger than the females in all instars. The molt increments of carapace width (CW) and carapace length (CL) did not differ between the sexes; the former decreased with growth, especially up to ~3–4 mm, whereas the latter did not change with growth. This may be due to the rapid growth in CW compared to CL during early ontogeny. The proportion of CW to CL was larger in the females than in the males, and the rate of increase in pleon width accelerated greatly after growth to ~4 mm CW. Cheliped dimensions were larger in males than in females, probably as a consequence of sexual selection. Cheliped propodus length and width increased with growth in both sexes, but the rates of increase tended to decelerate after ~7 mm CW in females. This indicates that females may allocate more energy to pleon growth while limiting cheliped growth.

Building confidence: Developing image-based methods to incorporate fishery-collected data in the American lobster stock assessment

The American lobster, Homarus americanus, supports the most valuable single-species fishery in North America; however to-date, a reliable and robust method to determine age does not exist, and thus some of the more traditional catch-at-age stock assessment methods cannot be used to determine status. In lieu of this, the Atlantic States Marine Fisheries Commission’s American Lobster Stock Assessment Model uses a probabilistic growth transition matrix to determine how lobsters of different sizes will grow and recruit into the fishery. Developing and updating the growth transition matrix to reflect current growth dynamics requires estimates of molt increment and interval. Tagging studies are an inexpensive method to collect this type of information, but relying on fishing industry reported recapture data and buy-in can be challenging, resulting in varied return rates and uncertainty in measurement accuracy. Here, we report on a subset of recaptured lobsters released in the Gulf of Maine and Georges Bank regions between 2015 and 2020, where in addition to recapture locations, harvesters were encouraged to submit images of recaptured lobsters alongside a standard lobster gauge as a scale to estimate carapace length. Some fishermen were able to provide both direct measurements and images. Images were analyzed in ImageJ to estimate individual lobster carapace length (CL); and each image was assigned a quality score. For all groups, image-derived lengths were correlated with measured observations, regardless of the overall image quality, with only a slight underestimation at the maximum end of CL. This image-based method for length estimation provides high-quality length predictions regardless of image quality and can significantly increase the likelihood of harvesters contributing data with broad potential to engage commercial fisherman in collaborative science. Using this method we were able to expand the dataset of length records from this project by 251 or 33 %, providing additional data at a rate similar to tagging an additional 6000 lobsters.

Resistance to initial starvation in stage I larvae of the American lobster Homarus americanus H. Milne Edwards, 1837 (Decapoda: Astacidea: Nephropidae)

Abstract Greater embryo mass confers an advantage in the face of sub-lethal starvation for larvae of the American lobster, Homarus americanusH. Milne Edwards, 1837. We reared larvae in the laboratory and recorded body size, molt increment, stage duration, and mortality during the three larval instars and postlarval stages. Larvae were either fed continuously or subjected to starvation periods immediately after hatching. Larval mass increased with embryo mass suggesting that energetic advantages of heavier embryos are conferred to the larvae. Stage I larvae hatched from clutches with heavier embryos and had lower mortality after five days without food. Stage I duration decreased with increasing embryo mass in treatments with initial periods without food of three, four, and five days. We also observed greater size increase at first molt and larger postlarval size in some treatments. Our results suggest that larger embryos produce larvae that are more resistant to starvation, which may provide a survival advantage when experiencing variable food supply due to the patchy distribution of their planktonic prey.

Infestation of Lithodes santolla by Eremitione tuberculata: spatial and temporal variations in parasite prevalence and effect on host growth.

The southern king crab (SKC) Lithodes santolla is a crustacean parasitised by the bopyrid Eremitione tuberculata. This study aimed to analyse spatial and temporal variations in E. tuberculata prevalence in the juvenile SKC population of San Jorge Gulf (SJG) and adjacent waters (Argentine Patagonia), and evaluate the effects of the parasite on SKC juveniles to improve our understanding of its impact as a disease on SKC health condition. Moult increment and body weight were compared between parasitised and unparasitised individuals. The prevalence of E. tuberculata in SKC juveniles varied both spatially and temporally. In the south of SJG, the prevalence was 54.5% (n = 11). Temporal prevalence analysis revealed values lower than 17.4% in mid SJG during May and September 2015. No significant differences were observed in E. tuberculata prevalence between sexes or among seasons. Eremitione tuberculata had a negative effect on SKC growth (lower body dry mass, moult increment and relative increment rate) in parasitised individuals. We hypothesised that the higher prevalence of E. tuberculata in the south SJG could be attributed to the retention of parasite larvae and the presence of the frontal system in this part of the gulf. The temporal variations could reflect host mortality. Our results suggest that bopyrid infestation may have a more important role than previously believed in the dynamics of the SKC population in mid-Patagonia.

Limited holding space reduces growth and behavioural performance in juvenile European lobsters

Conservation aquaculture offers important tools to secure sustainable animal supplies for human use. However, intensive aquaculture practices are increasingly raising concerns about the welfare conditions of farmed animals, which typically face high mortality rates due to diseases, cannibalism, and aggression. Here we focus on the European lobster (Homarus gammarus), an economically and ecologically important decapod species that has been subjected to conservation programs for decades. While standard husbandry procedures typically result into large numbers of juvenile lobsters produced and released, it remains poorly known whether such standard settings alter the development of behavioural and life-history traits of ecological importance for the animals to survive in the wild. Here, we investigate whether the size of the individual holding spaces affects the behavioural traits (exploration, space use, and sheltering) and growth (carapace length, intermoult period, and percentage moult increment) of juvenile lobsters during their early benthic stages. Our results offer solid evidence that rearing lobsters into small holding spaces not only limits and slows down their overall growth, but also compromises the development of ecologically-relevant behaviours that are essentials for these animals to survive in a complex and risky environment. We point the attention toward the benefits of adopting better rearing procedures to improve the welfare conditions of hatchery-cultured lobsters that can, in turn, result into faster growth rates and the development of competent behavioural repertoires of these valuable organisms—likely to improve the effectiveness of conservation programs.

Body length, dry and ash-free dry weights, and developmental changes at each copepodid stage in five sympatric mesopelagic aetideid copepods in the western Arctic Ocean

Abstract Aetideid copepods dominate the mesopelagic layer of the Arctic Ocean and play an important role in the vertical material flux and biodiversity. However, little information about the lengths and weights of their copepodids is available. In this study, we collected five sympatric aetideid copepods, Chiridius obtusifrons Sars G.O., 1902, Gaetanus tenuispinus (Sars G.O., 1900), Gaetanus brevispinus (Sars G.O., 1900), Aetideopsis multiserrata (Wolfenden, 1904), and Aetideopsis rostrata Sars G.O., 1903, from the Arctic Ocean and examined their body lengths, dry and ash-free dry weights, and developmental growths at each copepodid stage. Highly significant length-weight relationships were obtained among copepodids for all species. Within genera, individuals of the same length were heavier at shallower depths. This may result from the greater nutritional availability to species within genera inhabiting shallower depths. Common to all species, the organic content (ash-free dry weight per dry weight) was high for the early copepodid stages. This may be due to the residual organic content of lipid-rich eggs retained in the non-feeding nauplii. The largest growth in females occurred at C5/C6, whereas the largest growth in males occurred at C4/C5, as determined by moult increment and proportion of growth in weight. These sex differences in weight growth could be due to the degeneration of the feeding appendage and cessation of feeding in C6 males of aetideid copepods.

Climate-driven shifts in growth and maturity induce changes to the population and fishery dynamics of a high-value crustacean

Climate change is fueling unprecedented warming in marine environments. Crustaceans demonstrate strong physiological responses to rising temperatures including smaller molt increments, more frequent molting, and decreased size-at-maturity (SAM). Despite the potential for these changes to affect population and fisheries dynamics, there is limited research quantifying potential impacts. This is concerning, as crustacean fisheries are becoming increasingly important globally. Using an individual-based model for the valuable American lobster (Homarus americanus) fishery in the Gulf of Maine (GOM), we sought to address pressing questions about how climate-driven changes to growth and maturity could impact the population and fishery dynamics. To do so, we used counterfactual simulations informed by the literature and an expert survey to quantify the effects of smaller molt increments, increased molting, and decreased SAM on lobster spawning stock biomass (SSB) and landings. We found that all three changes to life history, combined, increased the SSB and landings relative to the base case. Notably, SSB in the terminal year of the time-series was 278.3%, 505.1%, and 748.5% greater than the base case under small, moderate, and extreme changes, respectively, to life history. However, when molt increment size and molting probability were changed but SAM was not, SSB and landings decreased relative to the base case, emphasizing the importance of SAM as a driver of productivity. Overall, these findings indicate that climate-driven changes to growth and maturity may favorably impact the population and fishery dynamics of lobster, contributing to sustained fishery yield in the GOM. This study emphasizes the utility of simulating the effects of climate-forced life history change for informing climate-ready fisheries management. Future work should explore the effects of other climate-driven life history changes alongside alternative management strategies for lobster and other crustaceans.

Effects of Temperature on Growth, Molting, Feed Intake, and Energy Metabolism of Individually Cultured Juvenile Mud Crab Scylla paramamosain in the Recirculating Aquaculture System

An eight-week experiment was conducted to investigate the effects of temperature (20, 25, 30, and 35 °C) on growth performance, feed intake, energy metabolism, antioxidant capacity, and the stress response of juvenile Scylla paramamosain in a recirculating aquaculture system. The results showed that the survival rate of the 35 °C group was 80.36 ± 5.92%, significantly lower than that of the other three groups (100%). The high molt frequency of mud crabs was observed in high-temperature groups, accompanied by a higher ecdysone level and ecdysone receptor gene expression but lower molt inhibitory hormone gene expression. However, the molt increment (73.58 ± 2.18%), food intake, and feed conversion efficiency showed a parabolic trend, with the lowest value found in the 35 °C group. Oxygen consumption rate and ammonia excretion rate increased with the increasing temperature, and oxygen-nitrogen ratio, lactic acid, triglyceride, total cholesterol, glucose, and cortisol peaked at 35 °C. Temperature also significantly affected the antioxidant system of S. paramamosain. Crabs in the 25 °C and 30 °C had a significantly higher total antioxidant capacity and lower malondialdehyde compared with the 35 °C group (p < 0.05). Although the high temperature promoted molting, it decreased the feeding rate and growth performance, leading to oxidative stress and functional hypoxia. The quadratic function model demonstrated the optimum temperature for the specific growth rate of juvenile S. paramamosain was 28.5–29.7 °C.

The effects of feeding ration and cheliped autotomy on the growth and expression of ecdysteroid receptor in early juvenile mud crabs, Scylla paramamosain

This study investigated the combined effects of feeding ration and cheliped autotomy on the intermolt duration, molting success, molt increments in size and weight, and ecdysteroid receptor gene (SpEcR) expression of early juvenile mud crab Scylla paramamosain. Newly molted second stage juvenile crabs (C2) were subjected to four feeding conditions; optimal, suboptimal (1/2 optimal), low (1/4 optimal) ration and starvation, and autotomy (intact vs. cheliped autotomy) in a 4 × 2 factorial design until all crabs successfully molted or died. A significant interaction of feeding ration and cheliped autotomy on intermolt duration was identified. With reduced feeding ration, both intact and cheliped autotomized crabs showed increased time and desynchrony of molting, but decreased carapace size and body weight. Importantly, all crabs with different feeding rations even the low ration had high rates of molting success (> 95%), while the crabs subjected to starvation died without molting. When fed optimal ration, the mean intermolt duration of the cheliped autotomized crabs was significantly prolonged, while no such effect was found between autotomized and intact crabs subjected to suboptimal or low feeding ration. The qRT-PCR revealed that the expression of SpEcR showed a general trend of inhibited by reduced feeding ration, which was consistent with observed significantly increased intermolt duration. Interestingly, the transcript level of SpEcR was only significantly affected by cheliped autotomy under the optimal and suboptimal feeding rations but not for the low feeding ration. Together, the results of this study suggest that the S. paramamosain early juveniles have a strong tolerance for fluctuations in food availability. In addition, the availability of food and limb autotomy could significantly affect growth, molting duration and synchrony of the crabs, which appeared to reflect in SpEcR expression level that involved in the regulation of molting and limb regeneration process of the juvenile crabs.

Analysis of biological and biochemical parameters of adult male spiny lobsters Jasus lalandii for identification of possible growth predictors

Biological body parameters of adult male West Coast rock lobsters, Jasus lalandii, of commercial size were analysed over two years to determine reserve accumulation during two moult (i.e. growth-) cycles. Two fishing areas were compared that were historically known for fast- and slow growth, respectively. In addition, setagenic development for moult stage determination and the biochemistry of the hepatopancreas were investigated from the fast growth area. This information was intended to confirm previously proposed predictors of annual male moult increment and identify potential new ones. Annual moult increments in these areas were determined from tag-and-recapture studies, including the seasons for which reserve accumulation was analysed. Data from the present study were not robust enough to confirm previously proposed predictors from peak accumulation months (March – May). Data arranged per moult stage were also unsuitable for prediction. Further results analysis, however, identified a subset of data that are potentially more useful: Hepatosomatic index HSI (+ 6 %), lipid content (+ 9 % ww, + 12 % wD) and lipid per whole hepatopancreas (+ 24 %) are all significantly higher in July 2011 than in July 2010, the last sampled months before the respective annual moult. These differences correlate with a 26 % (0.7 mm) faster growth during subsequent moult in 2011 than in 2010. Aspects of hepatopancreas lipid metabolism in the months prior to moult have therefore the potential to provide simple and robust predictors of growth in adult male J. lalandii. However, more research is required that also includes the months adjacent to July in more than one area and for a longer period than two years.

Effects of a reduction in algal nitrogen content on survival, growth, and reproduction of an herbivorous amphipod

Since nitrogen (N) is a limiting nutrient for many herbivores, variations in dietary N content will affect their fitness. In the Seto Inland Sea, Japan, the N content of green algae, Ulva spp., has in recent years shown a tendency to decrease due to the progress of oligotrophication. We investigated the effect of the reduction in N content of Ulva australis on the survival, growth, and reproduction of the herbivorous amphipod Ampithoe tarasovi under laboratory conditions. When amphipods were fed U. australis with a low N content, survivorship was not affected. However, the growth of both males and females was impaired due to the reduced molt increment and extended intermolt period. Furthermore, the low N content delayed female maturation and reduced the percentage of ovulation alongside the brood size and number of broods. These results suggest that the total number of eggs produced in the lifetime of a female in A. tarasovi is markedly reduced under low N food conditions. Therefore, in coastal waters where dissolved inorganic nitrogen (DIN) is deficient, because the tissue N content of algae reflects the DIN concentration in the ambient water, the population density of A. tarasovi may decrease due to the reduction in the number of viable offspring.

Direction, ontogeny, and mechanism of the temperature-size rule operating in a large marine crab, Chionoecetes opilio

Abstract The classic temperature-size rule (TSR) states that ectotherms mature smaller in warmer than in colder conditions; the reverse TSR is the opposite response. We combined field observations with laboratory experiments and published information to synthesise the response of snow crab (Chionoecetes opilio), a marine brachyuran with determinate growth, to temperature. Size at onset of physiological maturation/maturity and after terminal moult (TM) were positively related to temperature, thus indicating the reverse TSR. Moult increment varied little with temperature, but crabs were larger at instar in colder than in warmer water due to an initial difference in settlement size that propagated to higher instars, suggesting classic TSR prior to settlement. The pattern of increasing TM size with temperature was caused by crabs moulting more times before TM in warmer than in colder water. Intermoult period (IP) declined exponentially with temperature, and lower instars were more temperature sensitive than higher instars. Temperature effects on IP were strong enough to explain changes in size and instar number at TM under a possible time-invariant maturation schedule. Skip moulting was observed in the smallest crabs reared in the laboratory and resulted in high mortality. The reverse TSR in snow crab seems to be adaptive to coping with ectotherm predation.

From the Adriatic to Northern Norway—geographic differences in moult increment and moult probability of the European lobster (Homarus gammarus), across the natural range

Abstract This study collated existing data on lobster moult increment from studies across the range of Homarus gammarus, together with new tagging data from Orkney, United Kingdom. Generalized additive models were used to investigate geographical differences in absolute moult increment and moult probability. Absolute moult increment was seen to differ significantly between regions and between sexes and showed a non-linear relationship with pre-moult size. Smaller absolute moult increments were observed at southern and northern latitudes with larger increments observed in the centre of the species range. Temperature was identified as a significant factor explaining differences in absolute moult increment between regions, consistent with there being a thermal optimum for growth for in H. gammarus. Moult and double moult probabilities decline with pre-moult size, with greatest probability of moulting occurring around day 250. Probability of double moulting increased with mean annual sea surface temperature. Regionally variable growth patterns, and localized adaptation to abiotic variables such as temperature, should therefore be taken into account when defining lobster stock assessment and fishery management areas.

Parameter estimation of laboratory-reared Panulirus ornatus

In the fisheries study, fish growth is typically in an indeterminate fashion implying a continuous growth function occurs throughout the life. Most existing studies of fish trajectories are continuous; however, it is not true when modelling growth of the crustacean species with discontinuous growth paths. In this context, it is imperative to insure that a different type of model for describing absolute growth in crustaceans. Crustaceans must moult for them to grow. A moulting process is of periodical shedding of the exoskeleton and thus the crustacean growth is known to be a discontinuous process. The sudden growth of crustaceans through the moulting process makes the growth estimation more complex. To model the discontinuous growth, we consider stochastic approaches where the growth model only considers for a monotonically increasing function. To this end, we introduce a subordinator that is a special case of a Levy process. A subordinator is a non-decreasing Levy process, that enabling the individual variability and environmental perturbation to be included in modelling growth. A dataset in the laboratory setting (e.g. in an aquarium) is developed. The motivational dataset is from the ornate rock lobster, Panulirus ornatus, where the growth parameters can be estimated through two inter-correlated variables, namely the intermoult periods and the moult increments. We propose a joint density function, consisting of the moult increments and the intermoult periods. Both of these variables are assumed to be conditionally independent based on the Markov property. In the four-year studies from 1995 to 1999, the growth rates for females and males are estimated averagely 0.307 mm year–1 and 0.205 mm year–1, respectively. Therefore, the growth parameters of moult increments and intermoult periods can be quantified individually. The corresponding functions will then be convoluted through a simulation approach to obtain a population mean curve for crustaceans.

Growth of juvenile southern king crabs (Lithodes santolla) in San Jorge Gulf, Southwestern Atlantic Ocean

The southern king crab (SKC), Lithodes santolla, supports a lucrative fishery in San Jorge Gulf (SJG), Argentina and its adjacent area in the southwestern Atlantic Ocean. However, despite its commercial value, biological data on the SKC in SJG are scarce. In this study, we analyzed the growth of early juvenile SKCs by combining field and laboratory data. Sampling was carried out monthly in shallow waters in the central area of SJG (44°–46 °S). The sex and molt stages of SKC were recorded and the carapace length (CL) was measured. Individuals in premolt were taken alive to the laboratory to measure the molt increment. Size frequency distribution was used to assess modal progression, whereas the molt increments determined in the laboratory were used to verify the modal groups identified. Juvenile SKCs had molting activity throughout the year with no synchronization of the molt cycle observed. The molt increment ranged from 0.37 to 8.86 mm and the relative increment varied between 7.13 and 48.29 %. A total of 17 post-settlement modal groups were recognized: nine within the first year post-settlement, four within the second and three within the third. A wide variability in CL was recorded within the same annual class, which could be due to the absence of molting synchrony and the wide range of molt increment. Our results suggest that both male and female SKCs reach maturity four and a half years after settlement and that males recruit to the fishery seven years after settlement (at 110 mm CL).

Ontogenetic vertical migration of the mesopelagic carnivorous copepod Paraeuchaeta spp. is related to their increase in body mass

Abstract Two dominant mesopelagic carnivorous Paraeuchaeta copepods, Paraeuchaeta glacialis in the western Arctic Ocean and Paraeuchaeta elongata in the western subarctic Pacific, exhibited specialized ontogenetic vertical migration patterns with deeper occurrences of early copepodids (C1) and adults (C6F/M) and shallower occurrences of older copepodids C3−C5. Molt increments in body masses (wet, dry and ash-free dry masses) exhibited highly significant negative correlations with habitat depth. These facts suggest that both Paraeuchaeta species spend their reproductive (C6F/M) and early developmental (C1) stages in deeper layers to avoid predation and migrate upwards to where prey is abundant during the middle-late copepodid stages (C3−C5) to achieve greater mass growth.

A condition index based on dry weight as a tool to estimate in-situ moult increments of decapod shrimp: Investigating the effects of sex, year and measuring methods in brown shrimp (Crangon crangon)

The determination of in situ growth rates in crustaceans is a major obstacle for stock assessment, especially in short lived small shrimp species such as Crangon crangon. Here a new method is presented, which uses a condition index based on dry weight to predict growth increments. The method is based on a simple equation relating dry weights of shrimp and exuvia directly after moult with length measurements before and after moult. The parameter estimation of the model requires controlled moult experiments in the laboratory. In total 272 individuals moulted successfully within the first 2 days after capture, hence the increments reflected the feeding situation of the prior feeding period in the field. The results confirmed the validity of the method with data from two different years and demonstrated that in C. crangon the model parameters differ significantly between the two sexes. As a side product also moult intervals were estimated as a function of length and temperature. Moult increments were relatively shorter and more variable than previously found.

Effects of Sublethal Chlorpyrifos Exposure on Postlarval American Lobster (Homarus americanus).

The organophosphate pesticide chlorpyrifos has been introduced to the marine environment via adsorption to agricultural soil runoff or as spray drift. Chlorpyrifos affects the survival of some larval decapod crustaceans, but no data exist on the impacts to the American lobster, Homarus americanus. The purpose of the present study was to assess the levels at which chlorpyrifos affects the survival of postlarval H. americanus. Using acute saltwater exposures, the 24- and 48-h median lethal concentrations were established for stage IV H. americanus (1.56 and 1.33 µg/L, respectively). Movement, acetylcholinesterase activity, intermoult period, specific growth rate, and moult increment were measured during exposure to sublethal concentrations. Movement patterns were assessed to establish a 48-h median inhibition concentration for cessation of normal movement (0.66 µg/L). Acetylcholinesterase activity was found to be inhibited immediately post-exposure to 0.50, 0.57, and 0.82 µg/L chlorpyrifos but could be recovered within a period (9-15 d) in clean seawater. Sublethal growth effects of increased intermoult period, decreased specific growth rate, and decreased moult increment were observed during exposure to an environmentally relevant concentration (0.82 µg/L). The present study suggests that H. americanus stage IV larvae were marginally less sensitive to chlorpyrifos compared with other decapods and that acute lethality of H. americanus postlarvae is not likely to occur with chlorpyrifos concentrations previously reported from aquatic environments. Environ Toxicol Chem 2019;38:1294-1301. © 2019 SETAC.

Adapting the dynamic energy budget (DEB) approach to include non-continuous growth (moulting) and provide better predictions of biological performance in crustaceans

Abstract Dynamic energy budget (DEB) theory offers a comprehensive framework for understanding the overall physiological performance (growth, development, respiration, reproduction, etc.) of an organism over the course of its life cycle. We present here a simplified DEB model for the swimming crab Liocarcinus depurator. To the best of our knowledge, this is the first to be presented for this species. Most applications of the standard DEB model assume continuous growth in all size metrics (length, wet mass, carbon content) of the modelled species. However, in crustaceans growth, measured as an increase of carapace length/width, occurs periodically via moult. To account for this, we have extended the model to track the continuous increase in carbon mass as well as the episodic increase in physical size. Model predictions were consistent with the patterns in the observed data, predicting both the moult increment and the intermoult period of an individual. In addition to presenting the model itself, we also make recommendations for further development, and evaluate the potential applications of such a model, both at the individual level (e.g. aquaculture) and as a potential tool for population level dynamics (e.g. fisheries stock assessment).