Swimming Crab Portunus Trituberculatus Research Articles

Effect of dietary β‐carotene supplementation on growth and antioxidant capability of female swimming crab Portunus trituberculatus

AbstractDietary supplementation with synthetic β‐carotene was investigated in this study to assess its impact on gonad development, antioxidant status, color parameters, and carotenoid composition in adult female swimming crab (Portunus trituberculatus). Four diets, designated as Diet 1 to 4, were formulated to contain 3.07, 53.78, 103.23, and 205.22 mg/kg dry diets of synthetic β‐carotene. The findings revealed the following: (1) No significant differences in body weights or feed utilization were observed, indicating that β‐carotene did not significantly enhance the growth of adult P. trituberculatus. (2) The inclusion of 50–100 mg/kg β‐carotene in the diets led to improvements in antioxidant capacity indicators (T‐AOC, MDA) and immune‐related parameters (AKP, ACP) in both hepatopancreas and hemolymph. (3) Notably, the redness of ovaries and hepatopancreas increased significantly with higher dietary β‐carotene supplementation for color enhancement. In conclusion, incorporating β‐carotene into the diet enhanced the antioxidative capability, nonspecific immunity, and tissue carotenoid contents in adult female P. trituberculatus, and the optimal level of dietary synthetic β‐carotene supplementation for adult female P. trituberculatus was suggested to be around 100 mg/kg.

Reassembly and biotic sources of carapace bacterial community of Portunus trituberculatus after host molting

Crustaceans molt repeatedly during their development, which leads to frequent reassembly of their associated microbial communities. However, the reassembly of the carapace bacterial community (CBC) and its sources remain largely unclear. Here, these concerns were explored by investigating the succession pattern, assembly processes, and biotic sources of CBC of the swimming crab Portunus trituberculatus after host molting. Rhodobacteraceae, significantly discarded with the molted hard shell, was recruited during the 72 h postmolt. The early colonists such as Pseudoalteromonadaceae and Oeanospirillaceae had the higher physiological functional potentials for colonization, mainly via homogeneous selection. By contrast, the late colonists such as Flavobacteriaceae and Pseudomonadaceae had higher metabolic potentials and their colonization was governed by drift first and dispersal limitation later. The CBC was primarily shaped by multiple colonist pools, especially preceding carapace bacteria. Seawater had a higher contribution for CBC at the early stage than the late stage via providing the key bacteria mainly Rhodobacteraceae. These findings advance our understanding of the CBC and its reassembly pattern and sources, highlighting the importance of seawater bacteria for the early colonists. We also suggest the possibility and potential timing of using probiotics in the rearing water for the management of carapace microbiota in the aquaculture practice.

Selectivity of crab pots with escape vents and the optimal vent height for reducing the catch of sublegal swimming crab in the East China Sea pot fishery

Catching and subsequent discarding of sublegal-sized swimming crab Portunus trituberculatus in the pot fishery may result in increased unaccounted fishing mortality and contribute to overexploitation of the crab stocks in the East China Sea. Developing technical measures and implementing related regulations to improve the size selection of pots to reduce the catch of sublegal crab has become urgent. In this study, we evaluated the size selectivity of pots with rectangular escape vents of different opening heights (25 mm, 28 mm, 30 mm and 33 mm) through comparative fishing experiments and by employing the SELECT model. The results show that the installation of escape vents significantly reduced the catch per pot (in numbers) of total and sublegal swimming crabs, and significantly increased the proportion of legal-sized crabs for most vented pots except the 25 mm vent height. A significant positive linear relationship was found between escape vent height and the 50% retention carapace width, selection range and fishing power. Increasing the height of the escape vent had substantial effect on the exploitation pattern for swimming crab and the pot with a 28 mm height escape vent seemed to be the optimal design, releasing 67.4% of sublegal-sized crab and maintaining 94.8% of legal-sized crabs. Results showing that a pot with an escape vent that significantly reduces sublegal crab catch, while maintaining catch efficiency for legal-sized crabs, is positive for the fishery and supports the implementation of escape vents in the East China crab pot fishery.

Evaluation of spray-dried blood meal for application in commercial-like feed for juvenile swimming crab (Portunus trituberculatus)

The objective of the present study was to evaluate the effects of replacing fish meal (FM) with spray-dried blood meal (SDBM) on growth performance, antioxidant capacity, digestive enzyme activity, tissue Fe content, gene expression related to inflammation, and the TOR pathway in juvenile swimming crab (Portunus trituberculatus). Four isonitrogenous (47.0% protein) and isolipidic (9.0% lipid) diets were formulated to contain different levels of SDBM, with FM replaced by SDBM at 0, 10%, 20%, and 30%, respectively. The results showed that crabs fed diet SDBM30 exhibited the lowest survival among all treatments, and crabs fed the SDBM20 diet had the highest final weight, percent weight gain, specific growth rate and feed efficiency among all treatments. In addition, the protein content of the crab hepatopancreas decreased significantly and the lipid content increased significantly as SDBM replaced FM in the diets. Compared to other diets, crabs fed the SDBM30 diet had the lowest activities of antioxidant enzymes and the highest concentration of malondialdehyde in the hepatopancreas and hemolymph. The Fe contents in hepatopancreas and gill increased significantly, and the color of the hepatopancreas got darker as replacement of FM with SDBM increased from 0% to 30%. The expression of genes related to TOR (tor, akt, s6, and s6k1) and antioxidant (gpx) pathways in the hepatopancreas were down-regulated significantly with increased replacement of dietary FM with SDBM. In contrast, expression levels of genes related to protein translation (4ebp1, eif4e1a, eif4e2, and eif4e3) and inflammation pathways (myd88, traf6, relish, and irak4) were up-regulated significantly in crabs fed diets with SDBM supplementation. In summary, replacing FM with less than 20% of SDBM can promote the growth, but can darken the hepatopancreas, negatively affect antioxidant capacity, and induce an inflammatory response.

Combined effects of pentachlorophenol and nano-TiO2 with different sizes on antioxidant, digestive, and immune responses of the swimming crab Portunus trituberculatus

Marine nano-titanium dioxide (nano-TiO2) and pentachlorophenol (PCP) pollution are escalating concerns in coastal areas. This study investigated the combined effects of continuous exposure to nano-TiO2 (25 nm, 100 nm) and PCP (0, 1, 10 μg/L) for 28 days on the antioxidant, digestive, and immune abilities of the swimming crab Portunus trituberculatus. Compared with the control group, the interaction between nano-TiO2 and PCP was significantly higher than exposure to a single stressor, with a pronounced decrease in amylase activity observed due to the reducing nano-TiO2 particle sizes. Resulting in increased MDA and SOD activity. The expression levels of Toll4, CSP3, and SER genes in crab hemolymph showed perturbations following exposure to nano-TiO2 and PCP. In summary, according to the results of CAT, GPX, PES and AMS enzyme activities, it was concluded that compared to the larger particle size (100 nm), the single stress of nano-TiO2 at a smaller particle size (25 nm) and co-stress with PCP have more significant impacts on P. trituberculatus. However, the potential physiological regulation mechanism of the interaction between these pollutants remains elusive and requires further study.

Protein and lipid nutrition in crabs

AbstractUnderstanding the nutrition of crabs has a key role in ensuring the success and sustainability of their culture, as providing a well‐balanced, cost‐effective and sustainable diet that ensures the survival, growth and health of crabs is crucial. The present review is the first to focus primarily on the current state of knowledge of the nutrient requirements and related nutritional aspects in farmed crab species. The most common farmed and studied crabs are the Chinese mitten crab (Eriocheir sinensis Milne‐Edwards, 1853), giant mud crab (Scylla serrata Forsskal, 1775), green mud crab (Scylla paramamosain Estampador, 1949) and swimming crab (Portunus trituberculatus Miers, 1876). The article reviews how levels of dietary protein and lipid, the two most important and expensive macronutrient ingredients for most marine animals, directly affect reproduction, growth performance and survival of crabs, and the important impacts they have on immune response and antioxidant capacity. Furthermore, essential amino acids, and essential fatty acids, especially the long‐chain polyunsaturated fatty acids, as well as key lipid classes such as cholesterol and phospholipid will be discussed in terms of dietary requirements. Nutrient digestibility is a crucial method to determine protein quality, and studies on this topic in crabs were covered. The replacement of fishmeal and fish oil, as the predominant ingredients traditionally used in aquafeeds for marine animals, with more sustainable alternatives in diet formulations for crabs are also discussed. Modern ‘omics’ studies and high‐throughput technologies as fast‐growing approaches in protein and lipid research are also covered. Crabs generally require approximately 35%–50% protein, 5%–10% lipid, ~2.5% arginine, ~2.5% lysine, 1.5%–2.5% phenylalanine, 2.2% leucine, 0.7% tryptophan, 0.7% taurine, 1%–2% each of eicosapentaenoic acid, docosahexaenoic acid and arachidonic acid, 1% cholesterol and ~2% phospholipid in their diets.

Ghost fishing efficiency in swimming crab (Portunus trituberculatus) pot fishery

Abandoned, lost, or otherwise discarded fishing gear (ALDFG) is a global challenge that negatively affects marine environment through plastic pollution and continued capture of marine animals, so-called “ghost fishing”. In different pot fisheries, ghost fishing related to ALDFG is of concern, including pot fishery targeting swimming crab (Portunus trituberculatus). This study quantified the ghost fishing efficiency by comparing it to the catch efficiency of actively fished pots of the commercial fishery. The results showed that the ghost fishing affects both target and bycatch species. On average, the ghost fishing pots captured 12.53 % (confidence intervals: 10.45 %–15.00 %) undersized crab and 15.70 % (confidence intervals: 12.08 %–20.74 %) legal-sized crab compared to the actively fished pots. Few individuals of several bycatch species were also captured by ghost fishing pots. The results of this study emphasized the need to develop new management strategies for reducing marine pollution by ALDFG and associated negative effects in this pot fishery.

Changes in the physicochemical characteristics and microbial community compositions of the abdomen and cheliped muscles in swimming crab (Portunus trituberculatus) during frozen storage

The physicochemical indexes and microbial diversity were investigated to compare the altered quality properties of the abdomen and cheliped muscle in swimming crab (Portunus trituberculatus) during 100 days of frozen storage at −20℃. Over the extended duration of frozen storage, the sensory evaluation, moisture content, water activity (Aw), and water-holding capacity (WHC) in the abdomen and cheliped muscles of swimming crab decreased, while the pH, total volatile basic nitrogen (TVB-N), and trimethylamine (TMA) increased. The increase and decrease rates of these indicators were smaller in the abdomen than those in the cheliped muscle. High-throughput sequencing results indicated a reduction in the microbial richness and diversity in the abdomen and cheliped muscles of the swimming crab as frozen storage time extended. Proteobacteria, Actinobacteriota, and Firmicutes, Achromobacter, Kocuria, and Staphylococcus were the dominant phylum and genus in both muscle tissues, respectively. Furthermore, the correlation analysis between the composition of the microbiota and physiochemical properties revealed that the growths of Kocuria, Vibrio, Staphylococcus, and Aliiroseovarius were closely related to the physiochemical factors. The study provides a theoretical reference for quality deterioration and develops new products of different parts in the swimming crab during frozen storage.

Characterization of a pseudohemocyanin gene (PtPhc1) and its immunity function in response to Vibrio parahaemolyticus infection in the swimming crab Portunus trituberculatus

Pseudohemocyanin is a member of the hemocyanin superfamily, but little research is available on its function in immunology. In this study, a Portunus trituberculatus pseudohemocyanin gene, named PtPhc1, was obtained by gene cloning. The PtPhc1 cDNA was 2312 bp in length, encoding 684 amino acids while exhibiting a characteristic hemocyanin structural domain. Tissue expression analysis revealed ubiquitous expression of PtPhc1 across all tissues, with the highest level of expression observed in the hepatopancreas. The expression pattern of PtPhc1 in response to Vibrio parahaemolyticus infection was clarified using RT-qPCR in swimming crabs. Notably, the expression peaked at 24 h, and increased 1435-fold compared to the control group in the hepatopancreas. While the expression level reached the maximum value at 72 h, which was 3.24 times higher than that of the control group in hemocytes. Remarkably, the reduction in PtPhc1 expression led to a noteworthy 30% increase in the mortality rate of P. trituberculatus when exposed to V. parahaemolyticus. In addition, in vitro bacterial inhibition assays exhibited a dose-dependent suppression of bacterial proliferation by recombinant PtPhc1 protein, with a notable inhibition rate of 48.33% against V. parahaemolyticus at a concentration of 0.03 mg/mL. To the best of our knowledge, the results establish the function of pseudohaemocyanin in immunity for the first time, contributing to a deeper comprehension of innate immune regulatory mechanisms in aquatic organisms and advancing strategies for disease-resistant breeding.

The combined effects of microplastics and bisphenol-A on the innate immune system response and intestinal microflora of the swimming crab Portunus trituberculatus

Microplastics (MPs) and bisphenol-A (BPA) have been shown to have toxic effects on aquatic organisms. However, data on the combined effects of MPs and BPA on the innate immune system response and intestinal microorganisms of crabs are limited. Here, Portunus trituberculatus were exposed to BPA (at a concentration of 100 μg/L), MPs (microbeads of polystyrene with a particle size of 1 µm and at a concentration of 1 × 106 particles/L) or BPA+MPs for 21 days were tested at the tissue, cellular, and molecular levels. The results showed that neither the single nor combined exposure of MPs and BPA had a significant impact on the growth of crabs. However, intestinal histology study found that the intestinal villi of crabs in the BPA treated group, MP treated group and MP+BPA treated group appeared abnormal. Overall, compared with the control group and the single pollutant exposure group, co-exposure to the MP and BPA generally led to a significant increase in MDA and SOD activity and a significant decrease in CAT activity, and the activation of MyD88, Crustin-1, TARF6, Cu/Zn-SOD, Lyz, Toll-2 and NOX gene expression levels were significantly up-regulated. Co-exposure induced disorders of the intestinal microbial community of crabs, resulting in an increase in the abundance of harmful bacteria and a decrease in the abundance of beneficial bacteria. This study shows that the combined exposure of MPs and BPA can exacerbate the intestinal toxicity of a single pollutant to P. trituberculatus.

Dietary tributyrin supplementation promotes the growth by improving intestinal digestive and antioxidant capacity and the abundance of intestinal beneficial bacteria for swimming crab (Portunus trituberculatus)

This study aimed to evaluate the effects of tributyrin (TB) supplementation on the growth, digestive enzyme activity, lipid metabolism, and intestinal health of swimming crab (Portunus trituberculatus) with an initial weight of 12.50 ± 0.02 g. Six experimental diets were formulated, which containing 0%, 0.025%, 0.05%, 0.10%, 0.20%, and 0.40% of TB, respectively. Results showed that crabs fed the diet containing 0.10% TB had significantly higher values of percent weight gain (PWG) and specific growth rate (SGR) than those in other treatments. Crabs fed the diet without TB supplementation showed dramatically higher contents of T-CHO, TG, and MDA in serum than those in other treatments, opposite patterns were recorded for the activities of T-SOD, PPO, NO, ACP, and AKP. The activities of antioxidant enzyme including T-AOC, T-SOD, ACP, AKP and GSH-Px in hepatopancreas were significantly affected by dietary TB levels. Meanwhile, crabs fed the diet without TB supplementation had significantly lower activities of trypsin, lipase, and amylase in the intestine than those in other treatments. The relative expression levels of genes related to antioxidant capacity in the hepatopancreas and intestine were markedly decreased when crabs fed the diet without TB supplementation; however, crabs fed the diet without TB supplementation exhibited the highest expression of genes linked to inflammation among treatments, and the expression levels of crustin and lyso in the intestine were significantly affected by dietary TB levels. The expression levels of genes related to energy metabolism and intestinal immune barrier in the intestine were also influenced by dietary TB levels. Dietary TB supplementation could reduce lipid accumulation in hepatopancreas by upregulating lipid catabolism related genes expression levels and decreasing lipid anabolism related gene expression levels. Muscularis thickness, fold width, and fold height in the intestine were significantly increased with dietary TB increasing from 0% to 0.10%; moreover, lipid droplets, the diameter of R cells and the area of R cells in the hepatopancreas significantly decreased with an increase of dietary TB levels. Additionally, the number of Actinobacteria and Bacteroides significantly increased with an increase of dietary TB levels. To sum up, the TB requirement of swimming crab was 0.089% based on two slope broken-line analysis of PWG. The findings of the current study indicate that TB is an effective growth promoter that can serve as a nutritional supplement to improve the growth performance, promote health and regulate lipid metabolism of swimming crab.

Environmental enrichment improves survival and growth of Portunus trituberculatus in recirculating aquaculture system by reducing energy expenditure and stress responses

Barren rearing environment of recirculating aquaculture system (RAS) is a stressful situation that may result in high mortality rate of the swimming crab Portunus trituberculatus, an important economic seawater crab species in China. Environmental enrichment can mitigate stress to animals held in captivity. However, the physiological responses as well as survival and growth phenotype of the swimming crabs in the enriched RAS are currently unknown. Here, we examined the changes in the survival and growth performance as well as metabolic and immune features after 28 day-environmental enrichment using sand and polyvinylchloride (PVC) tube in RAS. We observed that sand enrichment improved survival and growth performance accompanied by reduced stress to crabs. The reduced stress subsequently attenuated the glucolipid metabolism and enhanced the accumulation of glycogen and triglyceride. This in turn mitigated oxidative stress and knock-on positive effects on immunity and apoptosis of the swimming crabs. PVC tube induced the similar but less significant effects on the swimming crabs to/than sand. Overall, environmental enrichment using sand and PVC tube improved survival and growth performance of the swimming crabs by reducing stress of RAS, glucolipid metabolism, oxidative damage and apoptosis, as well as enhancing accumulation of energy substances and immunity. The application of environmental enrichment techniques in RAS is urgently required to improve the yield of the swimming crabs.

The miRNAs let-7b and miR-141 Coordinately Regulate Vitellogenesis by Modulating Methyl Farnesoate Degradation in the Swimming Crab Portunus trituberculatus.

Methyl farnesoate (MF), a crucial sesquiterpenoid hormone, plays a pivotal role in the reproduction of female crustaceans, particularly in the vitellogenesis process. Despite extensive research on its functions, the molecular mechanisms that regulate MF levels during the vitellogenic phase remain largely elusive. This study investigates the roles of microRNAs (miRNAs), significant post-transcriptional regulators of gene expression, in controlling MF levels in the swimming crab Portunus trituberculatus. Through bioinformatic analysis, four miRNAs were identified as potential regulators targeting two genes encoding Carboxylesterases (CXEs), which are key enzymes in MF degradation. Dual luciferase reporter assays revealed that let-7b and miR-141 suppress CXE1 and CXE2 expression by directly binding to their 3' UTRs. In vivo overexpression of let-7b and miR-141 significantly diminished CXE1 and CXE2 levels, consequently elevating hemolymph MF and enhancing vitellogenin expression. Spatiotemporal expression profile analysis showed that these two miRNAs and their targets exhibited generally opposite patterns during ovarian development. These findings demonstrate that let-7b and miR-141 collaboratively modulate MF levels by targeting CXEs, thus influencing vitellogenesis in P. trituberculatus. Additionally, we found that the expression of let-7b and miR-141 were suppressed by MF, constituting a regulatory loop for the regulation of MF levels. The findings contribute novel insights into miRNA-mediated ovarian development regulation in crustaceans and offer valuable information for developing innovative reproduction manipulation techniques for P. trituberculatus.

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.

Effects of dietary histidine level on growth, antioxidant capacity and TOR signaling pathway in juvenile swimming crabs, Portunus trituberculatus

An eight-week feeding trial was conducted to determine the optimal dietary histidine requirement of juvenile swimming crab (Portunus trituberculatus). Six isonitrogenous and isolipidic diets (45.0% crude protein and 8.0% crude lipid) were formulated to contain 0.43%, 0.68%, 0.97%, 1.24%, 1.45% and 1.79% histidine, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile crabs (approximately initial weight 17.63 ± 0.08 g). The results indicated that the highest percent weight gain (PWG) and specific growth rate (SGR) was presented in crabs fed the diet with 1.24% histidine (P < 0.05). Crabs fed the diet with 1.45% histidine showed remarkably higher activities of alanine transaminase (ALT) and aspartate transaminase (AST) in hemolymph than those fed the other diets (P < 0.05). Meanwhile, the concentrations of malondialdehyde (MDA) in hemolymph and hepatopancreas remarkably decreased with dietary histidine levels increasing from 0.43% to 1.79%, and activities of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC) and hydroxyl radical scavenging activity in hemolymph and hepatopancreas exhibited the significant trend of first increasing to 1.17% histidine and then decreasing (P < 0.05). The concentrations of carnosine significantly increased with the increase of dietary histidine levels (P < 0.05). Moreover, dietary histidine levels could significantly influence the mRNA levels of genes related to TOR pathway such as tor, akt, s6k1, s6, eif4e1a, eif4e2 and eif4e3, and antioxidant such as cat, cMnsod, gpx, trx and prx (P < 0.05). Two slope broken-line model analysis of PWG against the dietary histidine levels indicated that the optimal dietary histidine requirement was estimated to be 1.17% of the dry matter (2.60% of the dietary protein) for juvenile swimming crab. In conclusion, dietary 1.24% histidine can significantly increase the carnosine contents in muscle, hepatopancreas and hemolymph, improve antioxidant performance and activate the TOR signaling pathway.

Response pattern of hemocyanin to Vibrio parahaemolyticus infection and its immune function in the swimming crab Portunus trituberculatus

Hemocyanin is a critical oxygen-transporting protein exhibiting multiple physiological functions, including protein storage and transportation, osmolarity regulation, molting, and immunomodulation in arthropods and mollusks. However, the immune function of hemocyanin in Portunus trituberculatus is rarely reported. Here, we identified ten subunit genes within the hemocyanin family from the P. trituberculatus genome. These genes exhibited conserved functional domains and copper ion binding sites. Building upon prior research, we specifically focused on investigating the immune functions of PtHc1 and PtHc2. Tissue expression analysis revealed that PtHc1 and PtHc2 were prominently expressed in the hepatopancreas and hemocytes. Upon infection with Vibrio parahaemolyticus, both PtHc1 and PtHc2 demonstrated a similar expression pattern, characterized by a gradual upregulation of expression levels in the hepatopancreas. While within the hemocytes, they exhibited a trend of initial downregulation followed by subsequent upregulation in expression. In addition, Recombinant hemocyanin was able to inhibit bacterial proliferation in a dose-dependent manner, with inhibition rates of 40 % and 39 % when the recombinant proteins of PtHc1 and PtHc2 reached 0.03 mg/mL, respectively. Besides, V. parahaemolyticus challenge resulted in a significant 20–23 % increase in mortality in P. trituberculatus following knockdown of PtHc1 and PtHc2. Overall, our study sheds light on the immune-related functions of PtHc1 and PtHc2 in P. trituberculatus, revealing their potential as key players in defending against pathogenic threats like V. parahaemolyticus. These results enriched the field of innate immunity in crustacean and providing a theoretical basis for disease resistance breeding.

Single nucleotide polymorphisms of the SIF gene and their association with growth traits in swimming crab (Portunus trituberculatus)

The swimming crab (Portunus trituberculatus) is an economically important aquaculture species in China. Mining candidate single nucleotide polymorphisms (SNPs) and genes associated with growth traits of P. trituberculatus is of great importance for the genetic breeding of this species. Among the genes associated with growth traits, “protein still life, isoforms C/SIF type 2 (SIF)” is thought to be an important gene affecting animal growth and development. In the current study, we investigated the SIF gene from P. trituberculatus to better understand its biological function. The full-length cDNA of SIF was 6185 bp, with a 5208 bp open reading frame encoding 1735 amino acids. Homology analysis showed that SIF shared 90.07% identity with Procambarus clarkii and 40.25–86.95% with other species. Expression pattern analysis of SIF in fast- and slow-growing groups revealed a significantly higher expression level in the former than in the latter (P < 0.05). qPCR studies revealed the ubiquitous expression of SIF in seven tissues tested, but most abundantly in the heart compared with muscle, testis, ovary, seminal vesicle, gill, and hepatopancreas (P < 0.05). A total of 38 SNPs in the UTRs and exons of SIF were screened and genotyped in 184 individuals of swimming crabs by targeted resequencing. Association analysis showed that four SNPs were significantly associated with growth traits (full carapace width, carapace length, body height, and body weight; P < 0.05). Two SNPs out of the four SNPs were shaped as a haploblock containing three haplotypes (GC, TA, and TC), and the TA haplotype showed significantly higher growth traits than the GC haplotype. Overall, the results provided potential candidate genes and SNP markers for the genetic improvement of growth traits in P. trituberculatus breeding.

Nutrient Composition of Ovary, Hepatopancreas and Muscle Tissues in Relation to Ovarian Development Stage of Female Swimming Crab, Portunus trituberculatus.

The swimming crab Portunus trituberculatus is one of the most important economic species in China and its mature ovary often determines its commercial value and production. Although the ovary maturation of crustaceans is generally affected by exogenous nutrition, the specific nutritional needs of ovary maturation of P. trituberculatus are poorly understood. To this end, we collected the P. trituberculatus samples with five ovarian maturation stages and measured their biochemical composition of the ovary, hepatopancreas, and muscle at each ovarian developmental stage. We further analyzed their relation to the ovarian developmental stage of P. trituberculatus by principal components analysis (PCA). We found the levels of branched-chain amino acids, long-chain polyunsaturated fatty acids (LC-PUFA), and monounsaturated fatty acids (MUFAs) in the ovary and hepatopancreas increased during the ovary maturation process, and also passively correlated with ovarian developmental stage, which highlights the necessity of these specific nutrients for oogenesis and for improving the nutrient quality of crabs. In addition, we found an increasing tendency of carotenoid content and phosphatidylcholine in phospholipid in the ovary from the pre-developmental stage to the proliferative stage, but not in the hepatopancreas and muscle, which highlights the possible involvement of carotenoids during the rapid oocyte development process. Our study may provide valuable information for developing a suitable broodstock diet that promotes the ovarian maturation of adult P. trituberculatus and ensures high-quality larval production.

A novel Vibrio alginolyticus phage and its therapy application in Portunus trituberculatus larvae

Ubiquitous pathogenic marine Vibrio alginolyticus is a very important pathogenic factor causing the outbreaks of sever vibriosis in marine-cultured animals broadly, an opportunistic pathogen for human, and a major pathogen associated with seafood. Antimicrobial drug resistances increased considerably, making the development of alternative therapeutics urgently needed. Isolation and characterization of V. alginolyticus phage vB_Va_Val-yong3 was performed. vB_Va_Val-yong3 contains an icosahedral head and a flexible tail. The diameter of the head is 62 ± 4 nm. The length and width of the tail is 110 ± 9.5 nm and 8 ± 1 nm, respectively. Its burst size is 87.5 PFU/cell. vB_Va_Val-yong3 is euryhaline, chloroform-tolerant, relatively UV-tolerant, stable at 4–50 °C and pH 5–12. Its genome size and GC content are 42,534 bp and 45.6%. It shared the highest nucleotide sequence similarity of 29.67% and the highest intergenomic similarity of 16.3% with all the other phages in PASC scanning and VIRIDIC scanning. Both the values were far below the threshold (> 70%) for genus definition, which illustrated that vB_Va_Val-yong3 revealed a novel phage genus. In the proteomic tree, vB_Va_Val-yong3 and three unclassified Vibrio phages (HY01, ST2-1pr and Seahorse) formed a clade, which clustered with two other clades representing the Mesyanzhionvvidriae family and the Casjensvidriae family respectively. VirClust analysis revealed that 27.7% of genes were shared between Vibrio phages vB_Va_Val-yong3, HY01 and ST2-1pr, which was higher than the family demarcation criteria (> 17%). Far <17% of genes shared between the three Vibrio phages and other viruses (including phage Seahorse and the phages of Mesyanzhionvvidriae and Casjensvidriae family). We advocate the establishment of a new phage family harboring Vibrio phages vB_Va_Val-yong3, HY01 and ST2-1pr. Phage therapy tests on swimming crab Portunus trituberculatus larvae were performed via immersion. vB_Va_Val-yong3 increased the survival rate of the larvae from 33.33% to 51.67% (p < 0.01). Very satisfactorily, the survivors of the infected larvae treated with vB_Va_Val-yong3 could molt and grow normally, while the survivors of the untreated larvae infected with V. alginolyticus all had the problems of molting and slow growth. This brings the very valuable results: all the survivors of the control groups were dwarf, while that of the experimental groups were normal. Food processing tests were also performed using vB_Va_Val-yong3 to eliminate V. alginolyticus in sashimi. The relative bacteriostatic rate of vB_Va_Val-yong3 in sashimi was 97.58% (p < 0.01). Results suggest that vB_Va_Val-yong3 has good potential to be developed as therapeutic agent against V. alginolyticus. This study enriches knowledge about Vibrio phages and lays a foundation for the application of the V. alginolyticus phage.

Identification of candidate genes associated with body weight in swimming crab (Portunus trituberculatus) according to conjunctive analyses of BSA-seq and RNA-seq

The swimming crab (Portunus trituberculatus) is a valuable crustacean species extensively cultivated in China, owing to its fast development, palatability, and rich nutrition. However, the genetic factors regulating its growth remain elusive, impeding the progress of breeding initiatives for this economically important species. In this study, we combined bulk segregation analysis sequencing (BSA-seq) and transcriptome sequencing (RNA-seq) to identify potential candidate genes related to the body weight of P. trituberculatus using a full-sib family. BSA-seq successfully identified five candidate intervals on chromosomes 31, 38, and 47, spanning a total length of 9.76 Mb, which encompassed 137 annotated genes. By conducting RNA-seq analysis on swimming crab individuals in two extreme weight groups, 1581 genes were mined as differentially expressed genes (DEGs), involving 357 up-regulated and 1224 down-regulated genes. GO enrichment analysis demonstrated that DEGs were significantly enriched in proteolysis, obsolete oxidation-reduction process, nucleus, cytoplasm, molecular function, and metal ion binding. KEGG enrichment analysis showed that the proteasome signaling pathway could play a prominent role in the growth difference of P. trituberculatus. The conjunctive analyses of BSA-seq and RNA-seq led to the identification of eight critical DEGs, including peripheral plasma membrane protein CASK (CASK), cytoplasmic dynein 2 heavy chain 1 (Dyh1b), RNA-binding protein 5 (Rbm5), structural maintenance of chromosomes protein 3 (Smc3), hemicentin-2 (Hmcn1), A-kinase anchor protein 13 (Akap13), zinc finger MYM-type protein 2 (Zmym3), and extracellular matrix protein FRAS1 (Fras1), which exert influence over the growth of P. trituberculatus. This study not only enhances our understanding of the molecular mechanism governing the growth of P. trituberculatus but also provides valuable insights for future aquaculture programs aimed at selective breeding of this species.