Swimming Crabs Portunus Trituberculatus Research Articles

The effects of water flow velocity and odor release frequency on the odor-tracking behavior of swimming crabs (Portunus trituberculatus)

Chemical-guided tracking is vital for critical activities such as foraging and mating in swimming crabs (Portunus trituberculatus), as it facilitates the detection and localization of odor sources. While water flow and odor release patterns are known to influence odor-tracking behavior, the specific mechanisms of their impact remain poorly understood. This study quantified the tracking behaviors of juvenile swimming crabs in response to varying water flow velocities (0.7 cm/s, 1.6 cm/s, and 2.5 cm/s) and odor release frequencies (0.5 Hz, 1.0 Hz, and 1.5 Hz). Results indicate that (1) at a flow velocity of 1.6 cm/s, crabs exhibited a higher proportion of tracking and success. Successful trackers at this flow velocity also demonstrated better tracking performance, including higher net-to-gross displacement ratios (NGDR), reduced gross displacements, shorter exit and track durations, and simpler tracking trajectories. (2) While odor release frequency did not significantly affect the proportion of tracking or success, the successful trackers at a higher frequency (1.5 Hz) had lower NGDR and higher gross displacements compared to those exposed to a lower frequency (0.5 Hz). (3) The successful trackers were not stastistically affected by the interaction between flow velocities and release frequencies. (4) In contrast to successful trackers, unsuccessful ones showed highly variable responses to flow velocity and odor release frequency, with generally inferior tracking performance. These findings provide valuable insights into the olfactory ecology of swimming crabs and can inform the optimized of aquaculture management and formulated feeds production.

Valine biased glycogen consumption to promote energy metabolism of Portunus trituberculatus and increased protein and essential amino acid deposition in muscle

The present research assessed the impact of dietary valine on nutritional and energy metabolism, as well as muscle development in swimming crabs (Portunus trituberculatus) over a period of six weeks. Swimming crabs, initially weighing around 23.34 ± 0.03 g, were given six diets identical in nitrogen and lipid levels (45 % and 8 % respectively). These diets contained valine contents of 0.99 %, 1.24 %, 1.56 %, 1.69 %, 1.90 %, and 2.20 % respectively. One hundred and eighty crabs were randomized into six treatments, each treatment including three replicates. The results suggested that significant increases were discovered in FW, PWG, as well as SGR of crabs when dietary valine increasing from 0.99 % to 1.69 %, but these measurements decreased when dietary valine increased to 2.20 %. Compare to the control treatment, crabs that were given diets with 1.90 % and 2.20 % valine showed increased level of muscle protein. Crabs that were given the diets containing 1.56 % and 1.69 % valine showed significantly increased concentration of GLU in hemolymph compared to the control group. Additionally, crabs that were given the diets containing 1.69 % valine and 1.90 % valine respectively showed significantly increased concentrations of T-CHO and TG in hepatopancreas. Hepatic glycogen concentration significantly decreased as the level of valine in diets increased from 0.99 % to 1.56 %, but significantly increased as valine level further increased to 2.20 %. Compared with the control group, crabs that were given diets with 1.90 % valine showed increased expression levels of genes associated to amino acid metabolism (pi3k, akt, alt, ast, 4ebp1 and eif4e3) and energy metabolism (pk, cs1, idh, nd1, cytb and cox2). Crabs given diets containing 2.20 % valine showed significantly increased expression level of pepck in hepatopancreas, while crabs given diets containing 1.24 %, 1.56 %, and 1.69 % valine exhibited significantly increased expression level of cpt1 in hepatopancreas. Crabs given the diet with 1.69 % valine had the highest expression levels of tor and pax7 in muscle. Increased dietary valine significantly reduced myofiber density but promoted higher frequency of myofibers in larger diameters. In conclusion, the optimal valine requirement for P. trituberculatus was 1.56 % of diet based on PWG by a quadratic modeling. 1.69–1.90 % valine promoted amino acid metabolism and muscle growth, moreover, enhanced energy metabolism by driving the consumption of glycogen rather than lipids.

The impact of noise on the stress response of Portunus trituberculatus in a land-based monoculture system

Human-induced noise, particularly from shipping and construction, significantly affects the stress responses of swimming crabs (Portunus trituberculatus Miers, 1876). Prolonged exposure can lead to stress responses, impacting the overall health of the crabs. This study aimed to assess how noise affects stress responses in P. trituberculatus. The sound had an intensity of 163 dB 1μPa for the noise condition and 114 dB 1μPa for ambient sound. P. trituberculatus was continuously exposed to the noise stimulus for six hours. Samples of serum, muscle tissue, gills, and hepatopancreas were collected at multiple time points: 0 min, 10 min, 30 min, 1 h, 3 h, 6 h, and 7 h. The serum cortisol levels in the noise-exposed group were significantly higher than those in the control group at 30 min and 6 h. The two groups had no significant differences regarding serum glucose and muscle lactic acid content. In the noise-exposed group, the gills exhibited significantly lower superoxide dismutase (SOD) levels. Conversely, for the hepatopancreas, the SOD levels in the noise-exposed group were notably lower than those in the control group at 10 min but significantly higher at 6 h and 7 h. Malondialdehyde (MDA) levels were substantially higher in the noise-exposed group than in the control group at 30 min and 6 h. This study demonstrates that P. trituberculatus experiences a physiological stress response to acoustic sounds.

Host-parasite interactions: a study on the pathogenicity of different Mesanophrys sp. densities and hemocytes-mediated parasitic resistance of swimming crabs (Portunus trituberculatus).

Mesanophrys sp. is a parasitic ciliate that invades and destroys the hemocytes of the swimming crab (Portunus trituberculatus). In the present study, we employed an in vitro model to elucidate how Mesanophrys sp. destroys crab hemocytes. We also evaluated the relationship between the parasite's density, the destruction rate of the hemocytes, and the rapid proliferation pattern of parasites in host crabs. We found that the survival rate and cell integrity of crab hemocytes decreased with an increase in Mesanophrys sp. density, depicting a negative correlation between hemocyte viability and parasite density. Further analyses revealed that crab hemocytes could resist destruction by a low density (10 ind/mL) of Mesanophrys sp. for a long time (60h). Mesanophrys sp. and its culture medium (containing the ciliate secretions) destroy the host hemocytes. The natural population growth rate of Mesanophrys sp. decreased with an increase in the parasite density, but the Mesanophrys sp. density did not affect the generation time of the parasites. In summary, Mesanophrys sp. can destroy crab hemocytes, and the degree of destruction is directly proportional to the parasite density. The resistance of crab hemocytes to Mesanophrys sp. decreased gradually with an increase in the parasite density.

Quality and Microbiome Analysis of Pickled Swimming Crabs (Portunus trituberculatus) during Storage at Two Alternative Temperatures

The storage quality and microbiome analysis of pickled swimming crabs (Portunus trituberculatus) stored at 20 and 4 °C were investigated. It showed that samples stored at 4 °C had a longer shelf life, lower total viable count (TVC), pH, and total volatile base nitrogen (TVB-N) contents than those stored at 20 °C. The biogenic amine (BA) results demonstrated that tyramine (tyr), putrescine (put), and cadaverine (cad) were the dominant amines in all samples, and samples stored at 4 °C had lower BA contents. A microbiome analysis indicated that a salt–alcohol water mixture significantly inhibited the growth of Tenericutes. Firmicutes, Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, and Cyanobacteria were the dominant bacteria of stored pickled crabs, and storage at 4 °C significantly inhibited the growth of dominant bacteria, more than that of 20 °C. In conclusion, 4 °C storage guaranteed the quality of samples by inhibiting changes in biochemical properties and the growth of dominant bacteria, thereby prolonging its shelf life.

Comparison of freezing and heating treatment sequence on biochemical properties and flavor of swimming crabs (Portunus Trituberculatus) meat during freeze-thaw cycles

The objective of this study was to compare the effect of freezing and heating treatment sequences on the biochemical properties and flavor of crab (Portunus trituberculatus) meat during freeze-thaw cycles. The results showed that pH, color, K and microstructure changes in the H-F group were not significant with increasing number of freeze-thaw cycles, but TVB-N values increased and WHC values decreased. However, with the increase in the number of freeze-thaw cycles, pH and WHC significantly decreased and TVB-N, L* and K values significantly increased in the C and F-H groups. Proteins were degraded in all groups, but the lower degree of degradation occurred in the H-F group. Although the total free amino acid content decreased with increasing number of freeze–thaw cycles in each group, the high content of AMP and IMP in the H-F group suggested that it still had a better flavor.

Establishment of CRISPR-Cas-based antiparasitic agents for the swimming crab parasite Mesanophrys sp.

Mesanophrys sp. represents a parasitic ciliate, significantly jeopardizing the survival of farmed swimming crabs (Portunus trituberculatus). However, certain drawbacks exist in traditional broad-spectrum antiparasitic drugs, necessitating the development of innovative antiparasitic methods. Here we report the development of a series of CRISPR-Cas-based antiparasitic engineering bacteria, termed AEB-Cas(s), capable of sequence-specific killing of Mesanophrys sp.. The AEB-Cas(s) are generated by introducing well-designed prokaryotic plasmid vectors into chassis bacteria to express CRISPR effector protein and guide RNA targeting the 18S rDNA, 28S rDNA, and DHC7 genes of ciliates. By virtue of the bacteria-feeding behavior of ciliates, a feeding-delivery (FD) strategy is established for the targeted delivery of exogenous proteins and RNAs into Mesanophrys sp.. Based on the FD strategy, AEB-Cas9 and AEB-Cas13 antiparasitic agents are feeding to the ciliates, and their antiparasitic effect on Mesanophrys sp. are evaluated, respectively. Our results demonstrate that AEB-Cas(s) exhibit significant differences in the inhibitory effect when targeting different ciliates' genes. Specifically, AEB-Cas9 and AEB-Cas13 exhibit 39.0% and 52.2% inhibition rates targeting the 18S rDNA gene, respectively. In comparison, the inhibition rates are 55.2% and 73.6% targeting the 28S rDNA gene, respectively. Notably, both exhibit the highest lethality targeting the DHC7 gene, with inhibition rates of 56.5% in AEB-Cas9 and 89.4% in AEB-Cas13, respectively. Our findings highlight the potential of AEB-Cas(s) as effective antiparasitic agents against Mesanophrys sp., and provide a promising approach for preventing and treating other aquatic ciliate diseases.

Effects of Ambient Ammonia‐Nitrogen Exposure on Uric Acid and Urea Metabolic Pathways and Tissue Distribution in the Swimming Crab Portunus trituberculatus

AbstractAmmonia‐nitrogen (ammonia‐N) is an important threat factor to the development of the crustacean breeding industry; however, information on nitrogen metabolism remains limited. In this study, effects of ammonia‐N on the metabolic pathways and tissue distribution of nitrogenous wastes were investigated in swimming crabs Portunus trituberculatus. The results showed that ammonia content in the hemolymph of crabs exposed to 1‐ and 5‐mg/L NH4Cl (ammonia‐N concentrations were 1.36 and 5.31 mg/L, respectively) significantly (P < 0.05) increased with time. The expression of xanthine oxidase was significantly up‐regulated in gills and muscles but was significantly down‐regulated in the hepatopancreas of crabs exposed to 1‐ and 5‐mg/L NH4Cl after 6–12 h. The expression of uricase was significantly up‐regulated in gills and muscles at 3 h, whereas it was significantly down‐regulated in hepatopancreas during 6–12 h but up‐regulated again after 24 h. Moreover, the expression levels of carbamoyl phosphate synthetase III and arginase were significantly up‐regulated in gills and muscles but significantly down‐regulated in the hepatopancreas of crabs exposed to 5‐mg/L NH4Cl after 6–12 h. Furthermore, under 5‐mg/L NH4Cl stress, trace amounts of uric acid were detected, which significantly increased in hepatopancreas and hemolymph at 3 h, in muscles at 6–12 h, and in gills at 6–24 h. In addition, similar to hemolymph ammonia, urea was also significantly increased after NH4Cl exposure. Moreover, uric acid was mainly stored in muscles and urea was primarily synthesized in the hepatopancreas. This study provides a theoretical basis for further study on the nitrogen metabolism mechanism in crustaceans.

Each Personality Performs Its Own Function: Boldness and Exploration Lead to Differences in the Territoriality of Swimming Crabs (Portunus trituberculatus).

The boldness and exploration of animals are closely related to their territoriality, with relevant studies having important applications in wildlife conservation. The present study establishes a behavior observation system measuring the boldness and exploration of swimming crabs (Portunus trituberculatus) to clarify the relationship between boldness, exploration, and territoriality, as well as to provide a behavioral basis for the construction of marine ranching. The behavioral tests of crabs in a safe environment (predator absence), a dangerous environment (predator presence), and habitat selection (complex and simple habitat) are analyzed. A territorial behavior score is calculated as an evaluation index of territoriality. The correlation between the swimming crabs' boldness, exploration, and territoriality is analyzed. The results show that there is no boldness-exploratory behavioral syndrome. In predator absence or presence environments, boldness is dominant in territorial behavior and positively correlates with territoriality. Exploration plays a vital role in habitat selection tests but has no significant correlation with territoriality. The experimental results preliminarily show that boldness and exploration jointly develop the difference in the space utilization ability of crabs with different personalities, improving the adaptability of swimming crabs in different conditions. The results of this study supplement the behavior rules of the dominant species of typical fishery resources in marine ranches, providing a basis for achieving animal behavior management function in marine ranches.

Effects of Different Habitat Space on Growth Performance and Nutritional Composition of Swimming Crabs (Portunus trituberculatus)

Habitat space is crucial for animals. This experiment explored the effect of four different farming acreages (0.5 m2, 1 m2, 10 m2, and 100 m2) on survival rate, growth performance, and muscle nutrition composition of swimming crabs (Portunus trituberculatus) at the farming density of 2 ind/m2. The results showed that the survival rate of the crabs that live in the 10 m2 group and live in 0.5 m2 alone had the highest survival rate of 20.50% and 20%, better than the 1 m2 group and the 100 m2 group with the lowest of 12.00% and 13% ( P < 0.05 ). There was no significant difference between final body weight and final carapace width among the 4 groups ( P > 0.05 ). The crude lipid content was the highest in 1 m2, which was significantly higher than in 0.5 m2 ( P < 0.05 ). The crude protein content in the 1 m2 and 10 m2 groups was significantly higher than that in the 0.5 m2 and 100 m2 groups ( P < 0.05 ). The results of the three conventional nutrients showed that there was no positive correlation between the muscle conventional nutrients and the farming area. The polyunsaturated fatty acid part of the 100 m2 and 10 m2 group was significantly different from the 1 m2 and 0.5 m2 groups ( P < 0.05 ). The results show that farming crab alone is not better than together, and a small aquaculture acreage helps to improve the muscle nutrition composition of the swimming crabs, while a large aquaculture acreage is more conducive to balance the development of nutrition. Overall, 10 m2 of habitat space was more economically feasible in practice.

Light Intensity and Photoperiod Interaction Affects the Survival, Development, Molting and Apoptosis-Related Genes of Swimming Crab Portunus trituberculatus Larvae

A 19-day experiment was conducted to investigate the optimal light intensity and photoperiod combination for larval swimming crabs Portunus trituberculatus in terms of survival, development, and apoptosis-related gene expression. Two photoperiods, i.e., 12 and 18 h photophases, and three light intensities, i.e., 126.08, 173.17, and 191.53 μmol m−2 s−1, were used in the study. The results showed that the cumulative survival rate (CSR) of larvae decreased with the increasing light intensity, and the adverse effect of high light intensity was only observed in long photophase groups. On the contrary, a long photophase and low light intensity elevated the CSR from zoea III to juvenile crabs. A long photophase also accelerated the development of zoea III larvae and upregulated the molting-related (ecr and rxr) and apoptosis-related (jnk, p53, and bcl-2) gene expressions. Taken together, the present study suggested that the light intensity and the photoperiod had a combined effect on P. trituberculatus larvae. The optimal light intensity and photoperiod for P. trituberculatus larvae were 126.08 μmol m−2 s−1 and an 18 h photophase, respectively.

Serotonin and dopamine regulate the aggressiveness of swimming crabs (Portunus trituberculatus) in different ways

Bioamines act as a pivotal part in the regulation of aggressive behavior in animals as a type of neuroendocrine, but the patterns of how they regulate aggressiveness in crustaceans are still unclear due to species-specific responses. To determine the effects of serotonin (5-HT) and dopamine (DA) on the aggressiveness of swimming crabs (Portunus trituberculatus), we quantified their behavioral and physiological characteristics. The results showed that an injection of 5-HT at 0.5 mmol L−1 and 5 mmol L−1 could significantly enhance the aggressiveness of swimming crabs, as well as an injection of DA at 5 mmol L-1. The regulation of 5-HT and DA on aggressiveness is dose-dependent, and these two bioamines have different concentration thresholds that can trigger aggressiveness changes. 5-HT could up-regulate the 5-HTR1 gene expression and increase lactate content at the thoracic ganglion as the aggressiveness enhances, suggesting that 5-HT may activate related receptors and neuronal excitability to regulate aggressiveness. As a result of DA injection at 5 mmol L-1, lactate content in the chela muscle and hemolymph increased, glucose content in the hemolymph increased, and the CHH gene was significantly up-regulated. Pyruvate kinase and hexokinase enzyme activities in the hemolymph increased, which accelerated the glycolysis process. These results demonstrate that DA regulates the lactate cycle, which provides substantial short-term energy for aggressive behavior. Both 5-HT and DA can mediate aggressive behavior in the crab by activating calcium regulation in muscle tissue. We conclude that the enhancement of aggressiveness is a process of energy consumption, in which 5-HT acts on the central nervous system to induce aggressive behavior, and DA affects muscle and hepatopancreas tissue to provide a large amount of energy. This study expands upon the knowledge of regulatory mechanisms of aggressiveness in crustaceans and offers a theoretical foundation for enhancing crab culture management.

High temperatures enhance the strength of multiple predator effects in a typical crab-clam system

Although marine heatwaves pose urgent threats to marine life, our understanding of how these events influence interactions between key species in marine ecosystems is still inadequate. Herein, we examined the behavioral mechanisms by which heat regulates multiple predator effects in different foraging systems that include Asian paddle crabs (Charybdis japonica) and swimming crabs (Portunus trituberculatus) by quantifying their predation and competition at two temperatures. Our results show that non-independent multiple predator effects occurred in the conspecific treatment of Asian paddle crabs and in the interspecific treatment, whereas independent multiple predator effects occurred in the conspecific treatment of swimming crabs. Asymmetrical behavior responses of these crabs to competition and heat triggered divergences in multiple predator effects. High temperatures increased the strength of multiple predator effects but did not alter their types. The reason is that heat negatively impacts predation by enhancing aggressive interactions, outweighing its direct positive effects on predation.

A baseline study on the distribution characteristics and health risk assessment of cadmium in edible tissues of the swimming crabs (Portunus trituberculatus) from Shanghai, China

This study analyzed the cadmium accumulation differences in edible tissues of the swimming crabs (Portunus trituberculatus) from Shanghai markets, which were mostly caught in the East China Sea, and the human health risk of cadmium from crabs consumption was evaluated. A total of 78 swimming crabs were collected, and the white meat and brown meat were separated for the cadmium analysis by Inductively coupled plasma mass spectrometry. The results revealed that there was difference in cadmium content in brown meat (1.260-16.303mg/kg) and white meat (0.005-0.542mg/kg). Furthermore, pollution index (Pi) results showed that only the claw muscle was at low contamination levels, while other edible tissues had varying degrees of contamination. Based on the health risk assessment by estimated daily intake (EDI), target hazard quotient (THQ) and target cancer risk (TCR), the consumption of the swimming crabs in Shanghai is considered safe, however, the accumulation of cadmium in the brown meat of swimming crabs deserves further attention and evaluation.

Shelter Color Selection of Juvenile Swimming Crabs (Portunus trituberculatus)

Color preference testing for animals is a prerequisite for optimizing facilities and ensuring animal welfare in aquaculture. Swimming crabs (Portunus trituberculatus) are aggressive, and shelters are often installed in ponds to reduce the high mortality rate caused by their agonistic behavior. To test the preference of juvenile crabs for the color of shelters, this study observes the preferences of crabs for shelters of different colors (white, yellow, blue, and black). The counts and duration of crabs occupying different colored shelters were quantified. The probability of fighting and the probability of abandoning the shelter were also calculated. The results revealed that: (i) when all colors were presented simultaneously, the z-scores of the blue shelters were far higher than others during the day; (ii) when only one color was present, crabs occupied the blue shelter significantly more often and for longer periods of time than others during the day, with invasive crabs exacerbating this preference; and (iii) the probability of fighting between crabs was relatively low in the presence of the blue shelter, and the probability of abandoning the shelter was significantly lower than that of others. Based on these results, blue shelters are recommended for use in swimming crab ponds.

Differences in Agonistic Behavior and Energy Metabolism between Male and Female Swimming Crab Portunus trituberculatus Based on the Analysis of Boldness.

Simple SummaryBoldness is a widely studied personality trait that is positively related to an individual’s willingness to fight. To explore the agonistic behavior between female and male crabs with different degrees of boldness, we quantified the boldness of females and males using a behavior observation system and used the experimentally determined boldness and classification. The results showed that boldness affected the agonistic behavior between female and male swimming crabs, the fighting willingness and capacity of male crabs is higher than that of female individuals and is higher in bold crabs than in shy individuals. Energy reserves and metabolic rates may be one of the factors affecting the agonistic behavior in crabs and that the agonistic behavior resulted in significant changes in key energy metabolites.Individual differences in metabolism and agonistic behavior have been a key research area in evolution and ecology recently. In this study, we investigated the boldness of swimming crabs Portunus trituberculatus and explored the agonistic behavior between female and male crabs, specifically examining competitions between bold females vs. bold males (BF–BM), bold females vs. shy males (BF–SM), shy females vs. shy males (SF–SM), and shy females vs. bold males (SF_BM) and its relationship with energy metabolism. The main results revealed the following: There was no significant difference in boldness between females and males, while there were more bold individuals than shy in both females and males. Bold individuals initiated significantly more fights than shy individuals, and male initiators won significantly more fights than female initiators. The duration and intensity of fight between bold individuals was significantly higher than fights between shy individuals. For males, the concentration of glucose in the hemolymph was significantly higher in shy crabs than bold crabs, while there was no significant difference between shy and bold individuals in females. After fighting, the concentration of glycogen in claws was lower than that before fighting, and the concentrations of glucose and lactate in hemolymph were significantly higher after fighting than before. We found that the fighting willingness and ability were higher in male crabs than females and higher in bold crabs than shy. Fighting ability varied between sexes and was influenced by boldness and energy state.

Genome characterization and comparative analysis among three swimming crab species

In this study we sequenced the genomes of three economically important swimming crabs Portunus trituberculatus, Charybdis japonica, and Callinectes sapidus using the next-generation sequencing approach and made a basic assembly. The genomes of the three species are characterized with high heterozygosity (>1.2%) and high repeat content (>50%). Genome comparative analysis revealed 40 long conserved fragments (>5,000 bp) among the three species, most of them are involved in cardiac-related biological process. Relative higher genome similarity was found between P. trituberculatus and C. japonica that are belong to different subfamilies, compared to that between P. trituberculatus and C. sapidus which are from the same subfamily. It is inconsistent with their phylogenetic evolutionary trees inferred from previous mitochondrial DNA coding fragments and a conserved ANK2 protein fragment from this study. We speculated that the high genome similarity between P. trituberculatus and C. japonica might be attributed to their same inhabit range in which the genome is subject to the same environment selection, and the inconsistence between genome similarity and phylogenetic relationship is caused by the different evolutionary rates of coding DNA and non-coding DNA under environment selection.

What Forms, Maintains, and Changes the Boldness of Swimming Crabs (Portunus trituberculatus)?

Simple SummaryThe formation and maintenance mechanism of personality is a hot topic in personality research. The boldness of the swimming crab (Portunus trituberculatus) has the greatest influence on its behavior, but the physiological factors leading to the stability of and difference in boldness are not yet clear. In this study, the factors affecting the formation and maintenance of and change in the boldness of swimming crabs are investigated from the perspectives of behavior, physiology, and neurotransmitters. The results show that the differences in boldness among crabs remain consistent for a long time and are closely related to the body’s energy and neurotransmitter metabolism.Boldness of personality is an important theme in animal behavior and has significant ecological and evolutionary consequences. Studies on boldness in crustaceans typically focus on their behavior, while relatively few studies have focused on the formation and maintenance of and change in boldness, such as energy metabolism and neurotransmission. In this study, we measured the boldness of swimming crabs (Portunus trituberculatus) and analyzed the relationship between boldness and oxygen consumption rate, energy concentration, and the relative expression of energy-metabolism-related and 5-HT genes in mRNA. The results showed that boldness remained stable across repeated tests but changed under dangerous conditions. Swimming crabs could be divided into bold and shy individuals. Bold individuals consumed oxygen at a significantly higher rate than shy individuals. Lactate and glucose concentrations in hemolymph were significantly lower in bold individuals than in shy individuals, and mRNA relative expression of Na+/K+-ATPase and 5-HT genes was significantly higher in bold than in shy individuals. Preliminary results indicate that energy metabolism and neurotransmitters may underlie the formation and maintenance of personality characteristics of swimming crabs. Swimming crabs also exhibit behavioral flexibility in order to cope with risks. This may be an adaptation to their complex environments.

Dietary cholesterol promotes growth and ecdysone signalling pathway by modulating cholesterol transport in swimming crabs (Portunus trituberculatus).

Cholesterol, as an indispensable nutrient, regulates molting and growth in crustacean. As crustaceans are unable to biosynthesize cholesterol de novo, it is central to understand how dietary cholesterol affects molting in crustaceans. An 8-week feeding trial was conducted to evaluate the effects of dietary cholesterol level (0.12%, 0.43%, 0.79%, 1.00%, 1.30% and 2.50%) on growth, cholesterol metabolism and expression of genes related to lipid and ecdysone metabolism in female swimming crabs (Portunus trituberculatus). A total of 192 crabs (1.41 ± 0.05 g) were randomly distributed into 192 aquaria. Each treatment had 4 replicates with each replicate containing 8 crabs. Crabs fed the 1.00% cholesterol diet showed best growth performance, and thus based on percent weight gain, the optimal dietary cholesterol requirement was calculated at 1.01%. Tissue cholesterol concentrations were positively correlated with dietary cholesterol level. The contents of functional fatty acids in hepatopancreas significantly increased as dietary cholesterol increased from 0.12% to 2.50% (P < 0.05). The expression levels of genes related to lipogenesis pathway, lipid catabolism and fatty acid oxidation were significantly down-regulated with increased dietary cholesterol level (P < 0.05). The highest expression levels of cholesterol transport genes, low-density lipoprotein receptor (ldlr) and low-density lipoprotein receptor-related protein 2 (lrp2) occurred in crabs fed the 1.30% cholesterol diet. Moreover, hormones related to molting such as crustacean hyperglycemic hormone (CHH), methyl farnesoate (MF), molt-inhibiting hormone (MIH), and ecdysone in hemolymph were significantly influenced by dietary cholesterol level (P < 0.05). The highest expression levels of ecdysone receptor (ecr) and chitinase 1 (chi1) in eyestalk and hepatopancreas were found in crabs fed the diet containing 1.00% cholesterol (P < 0.05). In conclusion, the optimal dietary level was beneficial to functional fatty acid accumulation, regulated lipid metabolism, promoted the ecdysone signalling pathway by improving the cholesterol transport, and improved the molting rate and growth of swimming crabs.

An evaluation of the preferences of the juvenile swimming crab, Portunus trituberculatus, for different structural properties of shelters

Crustaceans select shelters non-randomly, and their preferences may be mediated by the structural properties of shelters. Providing shelters is an effective approach to improving the survival of pond-raised crabs, but the structural properties of shelters that would significantly benefit the survival rate remain unclear. Here, a laboratory experiment was conducted to examine the preference of swimming crabs (Portunus trituberculatus) for three types of shelter with different depths, heights, and widths using an animal behavioral observation system. The residence time of crabs in each shelter was calculated, the changes in their preference were described by the program PFunc, and the correlations between the carapace width and preference function traits were analyzed. The results showed that juvenile swimming crabs (carapace width = 5.08 ± 0.34 cm) preferred shallow, high, and wide shelters, and the strongest preferences observed were for depth and height. There was a correlation between crab carapace width and preference function traits, which suggests that preferences became stronger as the carapace width increased. Height and width are the two major dimensions that need to be controlled when designing a shelter, and their value should be determined by the carapace width of the crabs. Providing the crabs with shelter at their preferred dimensions in the pond can prolong the residence time, which may help to reduce the frequency of agonistic encounters and improve the survival of the crabs.