Juvenile Crabs Research Articles

Quercetin supplementation improved the growth and health of juvenile Chinese mitten crabs (Eriocheir sinensis) fed low-fishmeal diets

The substitution of fishmeal with plant proteins can induce oxidative stress in aquatic animals and impair their growth and health. Quercetin is a potent natural antioxidant, but its specific effects on the growth and health of Chinese mitten crabs, as well as the underlying molecular mechanisms, remain unclear. This study aimed to investigate the impact of quercetin on the growth, physiological and biochemical parameters, gut microbiota, and transcriptome of juvenile Chinese mitten crabs (Eriocheir sinensis). Crabs (0.53 ± 0.01 g) were randomly divided into seven groups. One group was fed a diet containing normal fishmeal (35 % fishmeal), whereas the other six groups were fed diets containing low levels of fishmeal (15 % fishmeal) supplemented with different levels of quercetin (0, 250, 500, 1000, 2000, or 4000 mg/kg). Each group had four replicate tanks with 40 crabs per 300 L tank, and the experiment lasted for 56 days. The growth performance of the 35 % fishmeal group was significantly greater than that of the 15 % fishmeal group without quercetin. However, quercetin significantly increased the weight gain rate and specific growth rate of juvenile crabs, especially in the 1000 mg/kg quercetin group, where these rates exceeded those of the normal fishmeal group. The antioxidant capacity and immunity of the 35 % fishmeal group were significantly greater than those of the 15 % fishmeal group. However, quercetin supplementation promoted the antioxidant capacity and immunity of the crabs. Quercetin supplementation at 4000 mg/kg changed the gut microbiota structure by decreasing beneficial bacteria and increasing pathogenic bacteria. Quercetin supplementation enhanced the growth performance and antioxidant capacity of Chinese mitten crabs by increasing glutamate metabolism, pantothenic acid and Coenzyme A biosynthesis, sphingolipid metabolism, arachidonic acid metabolism, and cysteine and methionine metabolism. This study revealedthat dietary supplementation with quercetin can promote Chinese mitten crab growth, antioxidant capacity, and nonspecific immunity; improve gut morphology; and promote gut microbiota homeostasis. The optimal dietary concentration of 688–695 mg/kg is recommended on the basis of weight gain and specific growth rate analyses.

Dietary monosodium glutamate affects the growth and feed utilization of Eriocheir sinensis by regulating the appetite related genes expression

This study assessed the impacts of monosodium glutamate (MSG) on the growth performance, feed utilization, feed intake, and appetite regulation of Chinese mitten crab, Eriocheir sinensis. A total of 240 juvenile crabs (9.16 ± 0.21 g) were assigned to six experimental diets supplemented with MSG at 0 %, 0.20 %, 0.39 %, 0.59 %, 0.78 % and 0.98 %. The results demonstrated that 0.59 % MSG supplementation significantly enhanced the weight gain rate (WGR), specific growth rate (SGR), and feed utilization of juvenile E. sinensis by increasing feed intake (FI) (p < 0.05). Moreover, dietary moderate MSG improved the mid-intestine morphology, such as height of microvillus (HMV), width of microvillus (WMV), and thickness of muscularis (TM). The qRT-PCR analysis demonstrated that the mRNA expression levels of the appetite-stimulating neural signals agouti related protein (agrp) and ghrelin were increased significantly by dietary moderate MSG (p < 0.05). Conversely, the mRNA levels of protein kinase B (akt), target of rapamycin (tor) and 4E-binding protein (4e-bp), as well as appetite-suppressing neural signals pro-opiomelanocortin (pomc), corticotropin-releasing factor (crf) and peptide yy (pyy) were significantly down-regulated (p < 0.05). The two-slope broken-line regression analysis of SGR in relation to dietary MSG levels suggested that the optimum dietary MSG level for juvenile E. sinensis was 5.6 g/kg. Collectively, MSG may potentially stimulate or suppress the appetite regulation neural signals/hormones, thereby modulating the feeding behavior of E. sinensis.

One-Year-Old Precocious Chinese Mitten Crab Identification Algorithm Based on Task Alignment.

The cultivation of the Chinese mitten crab (Eriocheir sinensis) is an important component of China's aquaculture industry and also a field of concern worldwide. It focuses on the selection of high-quality, disease-free juvenile crabs. However, the early maturity rate of more than 18.2% and the mortality rate of more than 60% make it difficult to select suitable juveniles for adult culture. The juveniles exhibit subtle distinguishing features, and the methods for differentiating between sexes vary significantly; without training from professional breeders, it is challenging for laypersons to identify and select the appropriate juveniles. Therefore, we propose a task-aligned detection algorithm for identifying one-year-old precocious Chinese mitten crabs, named R-TNET. Initially, the required images were obtained by capturing key frames, and then they were annotated and preprocessed by professionals to build a training dataset. Subsequently, the ResNeXt network was selected as the backbone feature extraction network, with Convolutional Block Attention Modules (CBAMs) and a Deformable Convolution Network (DCN) embedded in its residual blocks to enhance its capability to extract complex features. Adaptive spatial feature fusion (ASFF) was then integrated into the feature fusion network to preserve the detailed features of small targets such as one-year-old precocious Chinese mitten crab juveniles. Finally, based on the detection head proposed by task-aligned one-stage object detection, the parameters of its anchor alignment metric were adjusted to detect, locate, and classify the crab juveniles. The experimental results showed that this method achieves a mean average precision (mAP) of 88.78% and an F1-score of 97.89%. This exceeded the best-performing mainstream object detection algorithm, YOLOv7, by 4.17% in mAP and 1.77% in the F1-score. Ultimately, in practical application scenarios, the algorithm effectively identified one-year-old precocious Chinese mitten crabs, providing technical support for the automated selection of high-quality crab juveniles in the cultivation process, thereby promoting the rapid development of aquaculture and agricultural intelligence in China.

High temperature aggravated hypoxia-induced intestine toxicity on juvenile Chinese mitten crab (Eriocheir sinensis)

High temperature and hypoxia in water due to global warming threaten the growth and development of aquatic animals. In natural or cultured environments, stress usually does not occur independently, whereas the synergistic effect of high temperature and hypoxia on Chinese mitten crab (Eriocheir sinensis) are rarely reported. In this study, 450 juvenile crabs were equally divided into control group (24 °C ± 0.5 °C, DO 6.8 ± 0.1 mg/L), hypoxia stress group (24 °C ± 0.5 °C, DO 1 ± 0.1 mg/L) and combined stress group (30 °C ± 0.5 °C, DO 1 ± 0.1 mg/L), and the intestinal health status, microbial diversity and metabolite profiles were evaluated for 24 h treatment. The results showed that hypoxia stress induced the expression level of pro-inflammatory related genes were significantly up-regulated in intestine of juvenile E. sinensis, and intestinal peritrophic membrane factor related genes were significantly down-regulated. High temperature further amplified the effects of hypoxia on pro-inflammatory and peritrophic membrane factor-related genes. Interesting, hypoxia stress induced a significant up-regulated of intestinal antioxidant-related genes, whereas high temperature reversed this trend. In addition, single stress or/and combined stress led to changes in intestinal microbiota diversity and abundance, and intestinal metabolite profiles. Compared with hypoxia stress, the synergistic effect of high temperature and hypoxia led to an increase in the abundance of pathogenic bacteria and a decrease in the abundance of probiotic bacteria. Moreover, intestinal metabolic pathways were significantly changed, especially amino acid metabolism and glycerophospholipid metabolism. Therefore, the results indicated that hypoxia stress could induce intestinal inflammatory response and oxidative stress, and lead to abnormal changes in intestinal microbiota and metabolic profiles, whereas high temperature further aggravate the toxic effects of hypoxia on the intestine. This study preliminarily revealed the synergistic toxic effects of high temperature and hypoxia on the intestine of juvenile E. sinensis.

Supplementation of yeast culture to low-fishmeal diets improves growth, intestinal health, and heat stress resistance in juvenile Chinese mitten crab (Eriocheir sinensis)

Yeast culture (YC), a microecological product derived from yeast fermentation, can enhance animal growth, health, and resistance to heat stress. However, its impact on the economically significant crustacean Eriocheir sinensis has not been demonstrated. This study investigated the effects of low-fishmeal YC on the growth, intestinal health, and heat stress resistance of juvenile Chinese mitten crabs. Crabs (0.72 ± 0.01 g) were distributed across 42 tanks, and 40 crabs were randomly maintained per tank in six replicates. The crabs were fed a control diet (35% fish meal) or six YC concentrations (15% fish meal; 0, 0.8, 1.6, 2.4, 3.2, or 4.0 g/kg) for 56 days. After sample collection, the remaining crabs were subjected to a 72-h heat stress challenge at 32 °C. A moderate-yield YC diet significantly improved weight gain, specific growth rate, and digestive enzyme activities (α-amylase, trypsin, and lipase) compared to those of crabs fed a 15% fishmeal diet without YC. Notably, the diet with 3.2 g/kg YC supplementation was performed as well as crabs fed a 35% fishmeal diet. YC also enhanced intestinal morphology in the low-fishmeal diet group and reduced oxidative damage by increasing the expression of genes related to the peritrophic membrane and tight junction proteins. Furthermore, YC supplementation diversified the intestinal microbiota, significantly increased the abundance of Firmicutes and the genus Shewanella, increased acetate and butyrate levels and decreased the abundance of Proteobacteria. Correlation analysis revealed that weight gain and specific growth rate were associated with most digestive activity and intestinal health indicators. Following heat stress challenge, YC protected against oxidative stress and enhanced serum immunity at elevated temperatures. This study indicated that incorporating YC in low-fishmeal diets significantly increases juvenile crab growth, improves intestinal health, and mitigates oxidative stress induced by temperature elevation. The optimal YC concentration was determined to be 2.71 g/kg through regression analysis.

Spatiotemporal variation in size and abundance of juvenile Chinese mitten crab (Eriocheir sinensis) in Yangtze Estuary

IntroductionIntertidal habitat preferences and spatiotemporal variation in the abundance of juvenile Chinese mitten crab Eriocheir sinensis in Yangtze Estuary are reported.MethodsThe size and abundance of this crab are reported for mud flat, gravel, root belt, and marsh habitats in this estuary’s lower, middle, and upper reaches from June 2021 (spring) to February 2022 (winter) using quadrat method.ResultsJuvenile E. sinensis of carapace length (CL) 5.5 ± 2.1 mm (mean ± standard deviation) were collected; no juveniles were found in February 2022. Crab abundance in root belt and gravel habitats usually exceeded that of marsh habitat; no juveniles were found in mud flat habitat. The greatest abundances and smallest individuals were found when megalopa recruited in early spring (June); juvenile abundance decreased sharply afterwards, and crabs were absent from the intertidal during winter. Size and relative growth rate of juvenile crabs were greater in root belt and gravel habitat than in marsh habitat from June to August. Recruitment primarily drove changes in crab abundance and size during June and July, and temperature best correlated with changes in the winter. Many stage I juveniles (CL &amp;lt; 3.1 mm) occurred in the lower estuarine reaches, while stage III and IV juveniles (CL 3.9–6.5 mm) primarily occurred in the middle and upper estuarine reaches.DiscussionAlthough intertidal wetland habitat in Yangtze Estuary is severely degraded and reduced in area, it remains important for recruitment and maintenance of mitten crab populations. An understanding of the habitat requirements of this species will benefit management of this crab resource and the prioritized restoration of intertidal habitat.

Effects of background color on survival, growth, and shell coloration of juvenile Chinese mitten crab (Eriocheir sinensis)

Background color is a crucial factor influencing the growth performance and feed utilization in crustaceans. However, little is known about its impacts on the culture performance of Chinese mitten crab (Eriocheir sinensis). In this study, we examined the impacts of six different background colors (white-W, black-BK, green-G, red-R, yellow-Y, and blue-BL) on growth, inter-molt period, and coloration and total carotenoids content of carapace of juvenile E. sinensis. The culture experiment comprised two trials: a 68-day individual culture, and a 30-day group culture. Individual culture results: No significant effects of background color were found on weight gain rate (WGR), specific growth rate (SGR), molting interval, carapace length and width, and survival rate (SR) of the juvenile crabs (P > 0.05). However, during the second molting cycle, the BL group exhibited the highest WGR, and the G group showed the lowest hepatopancreas index (HSI). Meanwhile, markedly lower feed conversion ratio (FCR) was obtained for the W group compared to the G and BK groups. Group culture results: Significantly higher SR was recorded for the BK group, and the highest limb loss rate was detected for Y group indicating the significant effects of background color on survival and aggressiveness of juvenile E. sinensis. Moreover, background color impacted the carapace coloration indices where the W, BK and Y groups showed the highest brightness (L*), redness (a*), and yellowness (b*) values, respectively. Furthermore, correlation analysis revealed a positive linear relationship between the L* value and background color (y =0.1638x+27.961, R2=0.613). In conclusion, our results demonstrated that background color significantly affects culture performance and carapace color. Black background color was shown to enhance the survival rate and reduce the limb amputation rate under group culture condition. These results provide new insights on the optimization of farming technology for juvenile E. sinensis.

Toxicity, Oxidative Stress, and Tissue Distribution of Butachlor in the Juvenile Chinese Mitten Crab (Eriocheir sinensis)

The Chinese mitten crab (Eriocheir sinensis) is one of the most commercially important crustacean species in China. The aim of this study was to characterize the toxic effects of butachlor (an herbicide of the acetanilide class) on juvenile E. sinensis crabs. The lethal effects and the acute toxicity of butachlor on juvenile E. sinensis specimens were assessed through a semi-static in vitro experiment. We determined the activities of superoxide dismutase (SOD) and catalase (CAT) as well as the levels of glutathione (GSH) and malondialdehyde (MDA) in the gills and the hepatopancreas of the juvenile crabs, at different time points over a 14-day short-term exposure to butachlor. Moreover, we measured the residual levels of butachlor in three different tissues (gills, hepatopancreas, and muscles) of the juvenile crabs over a longer period. Our findings revealed that butachlor is highly toxic for juvenile E. sinensis crabs. In fact, the median lethal concentration (LC50) values of butachlor at 24, 48, 72, and 96 h were found to be 4.22, 1.84, 0.34, and 0.14 mg/L, respectively, while the safe concentration was 0.014 mg/L. The antioxidant defense ability of the juvenile E. sinensis crabs against butachlor was induced after exposure to the herbicide at a concentration of 0.01 mg/L. After 14 days of exposure to butachlor at 0.04 and 0.16 mg/L, both SOD and CAT were found to be significantly inhibited (p &lt; 0.05), the GSH levels were found to be significantly decreased (p &lt; 0.05) and the MDA levels were identified as significantly increased (p &lt; 0.05). Moreover, after 14 days of exposure to butachlor at 0.16 mg/L, the activities of SOD and CAT as well as the content of GSH in the hepatopancreas were found to be significantly decreased (p &lt; 0.05). Our results revealed that a high concentration of butachlor was capable of inducing oxidative stress and damage in juvenile E. sinensis crabs. The maximal residual value of butachlor was obtained in the gills, with a content of 4.56 μg/kg. Butachlor was not detected after 24 days in the aforementioned three tissues of the juvenile crabs, thereby indicating that it was effectively metabolized.

Evaluation of earthworm meal (Eudrilus eugeniae) as fish meal replacement in juvenile Mangrove Crab (Scylla serrata) diet

Two feeding trials were conducted to evaluate the performance of the earthworm (Eudrilus eugeniae) meal (vermimeal) as a replacement for fish meal in the diet of juvenile mangrove crab (Scylla serrata) in terms of growth, feed efficiency, intermolt duration, carapace width increment, molting success, survival, and incidence of cannibalism. Four experimental diets were formulated with 0, 25, 50, and 75% fish meal protein replaced with earthworm meal protein, designated as D0, D25, D50, and D75, respectively. In the first feeding trial, the experimental diets were fed to crablets with an initial average weight of 0.09±0.007g. Each replicate comprised ten (10) crablets individually stocked in 750ml-capacity plastic containers randomly distributed in a static water bath. Final weight gain, feed efficiency and survival were measured after the 5th molt. In the second feeding trial, 150 crablets with an average weight of 0.07±0.002g were stocked at 30 crablets each in five (5) replicate tanks. Survival and incidence of cannibalism were monitored daily until the end of the culture period of 30 days. The first study showed that the growth of mangrove crab juveniles fed the diet with up to 50% of the fish meal protein replaced by the earthworm meal protein was statistically comparable to the control group. The survival of crablets in the second feeding trial was highest in D25 (33%), followed by D50 (29%), D0 (18%), and lowest in the group fed with D75 (13%). Overall, earthworm meal (Eudrilus eugeniae) can replace as much as 50% of the fish meal protein in juvenile mangrove crab (Scylla serrata) diet without negative effects on growth, carapace width increment, feed efficiency, intermolt duration, molting success, survival, and cannibalism.

Involvement of Histone Acetyltransferase 1 (HAT1) in the Spermatogenesis of Non-Condensed Nuclear Sperm in Chinese Mitten Crab, Eriocheir sinensis.

Chinese mitten crab, Eriocheir sinensis, is a decapod crustacean with a special, non-condensated nucleus in the sperm. Studies have shown that the nuclear compact state of male germ cells during the spermatogenesis is closely related to histone modification. To explore the possible role of histone acetyltransferase 1 (HAT1) in the chromatin organization during the E. sinensis spermatogenesis, we took the testis tissues of both adult and juvenile crabs as the materials of study and analyzed the biological functions of HAT1 by whole transcriptome sequencing and bioinformatics, then further analyzed the expression and distribution of HAT1 using the methods of RT-qRCR, western blotting, and immunofluorescence location. The results showed that HAT1 is an alkaline-unstable hydrophilic protein. Itwaspredictedtointeractwith a variety of histones and chromosome assembly proteins, including Asf1b, Chaf1b, and Hist1h3f, and is involved in many biological functions pertaining to chromatin dynamics such as chromatin organization, DNAdependent nucleosome assembly, DNA conformational changes, and so on. HAT1 was up-regulated in the adult testes compared to the juvenile (n = 3, P < 0.05). HAT1 was mainly located in the nuclei of male germ cells of E. sinensis. As spermatogenesis proceeded, the expression of HAT1 decreased and evendisappearedinthenuclei (n = 3, P < 0.05). HAT1 is an important player in histone acetylation, which facilitates chromatin alteration in a three-dimensional conformation. The expression of HAT1 in different male germ cells might indicate the chromatin dynamics at the diversity stages of spermatogenesis. The high expression of HAT1 at the early stages of E. sinensis spermatogenesis hints the active involvement in chromatin organization, while its progressively reduced expression accompanied by the progression of spermatogenesis suggests a relatively gradual stabilization and stereotyping of chromatin. As for the disappearance of HAT1 in mature sperm with non-condensed nuclei, the reduction in histones targeted by HAT1 or histone acetylation may be an important initiator.

Gender Identification of Chinese Mitten Crab Juveniles Based on Improved Faster R-CNN

The identification of gender in Chinese mitten crab juveniles is a critical prerequisite for the automatic classification of these crab juveniles. Aiming at the problem that crab juveniles are of different sizes and relatively small, with unclear male and female characteristics and complex background environment, an algorithm C-SwinFaster for identifying the gender of Chinese mitten crab juveniles based on improved Faster R-CNN was proposed. This algorithm introduces Swin Transformer as the backbone network and an improved Path Aggregation Feature Pyramid Network (PAFPN) in the neck to obtain multi-scale high-level semantic feature maps, thereby improving the gender recognition accuracy of Chinese mitten crab male and female juveniles. Then, a self-attention mechanism is introduced into the region of interest pooling network (ROI Pooling) to enhance the model’s attention to the classification features of male and female crab juveniles and reduce background interference on the detection results. Additionally, we introduce an improved non-maximum suppression algorithm, termed Softer-NMS. This algorithm refines the process of determining precise target candidate boxes by modulating the confidence level, thereby enhancing detection accuracy. Finally, the focal loss function is introduced to train the model, reducing the weight of simple samples during the training process, and allowing the model to focus more on samples that are difficult to distinguish. Experimental results demonstrate that the enhanced C-SwinFaster algorithm significantly improves the identification accuracy of male and female Chinese mitten crab juveniles. The mean average precision (mAP) of this algorithm reaches 98.45%, marking a 10.33 percentage point increase over the original model. This algorithm has a good effect on the gender recognition of Chinese mitten crab juveniles and can provide technical support for the automatic classification of Chinese mitten crab juveniles.

Performance Parameters of Paralarvae and Postparalarvae Rearing of Patagonian Red Octopus, Enteroctopus megalocyathus, under Experimental Conditions

Patagonian red octopus, Enteroctopus megalocyathus, an interesting species for Chilean aquaculture diversification, requires the improving of their experimental technology to obtain early juveniles. The first objective of the study was to enhance aspects of feeding and temperature management in broodstock, egg incubation, paralarvae rearing, and early juveniles’ growth. The results indicated that female weight decreases up to 46.0 ± 8.6% during the egg incubation. Test of 8, 14, and 18°C during egg incubation shows that at 18°C embryos do not survive. Paralarvae reared under four diet treatments: (1) unfed, (2) enriched Artemia (Nannochloropsis sp.), (3) copepod (Acartia spp.), and (4) juvenile crabs (Petrolisthes spp.) showed survival quadruplication when they fed copepods and crabs instead of Artemia. Juveniles reared at 11, 13, and 15°C improved feed conversion and protein efficiency ratios at 15°C. The second objective was to analyze batches of paralarvae and early juveniles of two different periods to obtain their performance indicators and to compare them between productive periods. The results of growth rates, the relative weight condition coefficient, and morphometric relationships are discussed in the context of paralarvae culture from 1 to 90 days after hatching (DAH) and early juveniles from 1 to 135 days postsettlement (DPS).

Seasonal dynamics of intestinal microbiota in juvenile Chinese mitten crab (Eriocheir sinensis) in the Yangtze Estuary.

In this study, the seasonal differences in the intestinal microbiota of Chinese mitten crab (Eriocheir sinensis) larvae were investigated at different sites in the intertidal zone of the Yangtze River Estuary. 16S rRNA high-throughput sequencing technology was used to compare and analyze the microbial community structure in the intestines of juvenile crab from different seasons. The results showed that the main microbial phyla in all seasons and sites were Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria, which accounted for 97.1% of the total microbiota. Composition analysis revealed that the relative abundance of Proteobacteria decreased from summer to winter at each station, whereas Bacteroidetes showed the opposite trend. Alpha diversity analysis showed that species richness increased from summer to winter at the upstream site (P < 0.05), but decreased at the downstream site (P < 0.05), with no significant differences observed in other comparisons. Biomarker species analysis showed that juvenile crab exhibited a more specialized microbial community in summer compared with autumn and winter. Co-occurrence network analysis revealed that microbial interaction network complexity was lower in autumn compared with summer and autumn. Functional prediction analysis showed that the microbial community only exhibited seasonal differences in amino acid biosynthesis, cofactor, prosthetic group, electron carrier, and vitamin biosynthesis, aromatic compound degradation, nucleotide and nucleoside degradation, and tricarboxylic acid cycle pathways. The results indicated that the microbiota did not significantly differ among sites, and seasonal variation was a main factor influencing the differences in intestinal microbiota of Chinese mitten juvenile crab. Moreover, the microbial community was more complex in summer compared with autumn and winter.

Effects of soy isoflavones on growth performance, antioxidant capacity, non-specific immunity and lipid metabolism of juvenile Chinese mitten crab, Eriocheir sinensis

Soy isoflavones are phytoestrogens that provide protection against some hormonal disorders and regulate several physiological functions in animals. This study investigates the effects of soy isoflavones on body composition, antioxidant activity, non-specific immunity, and lipid metabolism in juvenile Chinese mitten crabs, Eriocheir sinensis. A total of 960 juvenile crabs (1.09 ± 0.01 g) were randomly assigned to 24 tanks (300L), with 40 crabs in each tank in four replicates. The crabs were fed diets (43.5% protein and 7% lipid) with six levels of soy isoflavones (0, 8.8, 15.8, 33.8, 66.8, and 137.0 mg/kg) at 4% BW/day for 56 days. The final biomass and biomass gain of crabs supplemented with 15.8 and 33.8 mg/kg soy isoflavones were significantly higher than those in the control group. The total lipid content in the whole-body and hepatopancreas of the crabs fed 15.8 and 33.8 mg/kg soy isoflavones was significantly lower than in the control group. Compared with the control group, soy isoflavones significantly enhanced the activities of superoxide dismutase, glutathione peroxidase and total antioxidant capacity in the hepatopancreas by 40%, 57% and 79%, respectively, and significantly decreased malondialdehyde content by 24%. The high dietary soy isoflavones levels increased total protein and hemocyanin contents in hemolymph, and alkaline phosphatase activity was also significantly enhanced. The triglyceride contents in the hepatopancreas and hemolymph were significantly lower in the soy isoflavones-supplemented group. Dietary soy isoflavones may reduce lipid accumulation in the hepatopancreas by repressing genes related to lipid synthesis and promoting the expression of lipid oxidation and transport genes. The broken-line model analysis of biomass gain against dietary soy isoflavones levels shows that the optimal supplemental level of soy isoflavones for juvenile crabs is approximately 26.66 mg/kg. Thus, this study suggests that dietary soy isoflavones supplementation can improve growth performance and health and reduce lipid accumulation in the hepatopancreas of juvenile crabs.

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.

Microcystin-LR-induced autophagy via miR-282–5p/PIK3R1 pathway in Eriocheir sinensis hepatopancreas

With the intensifying climate warming, blue-green algae blooms have become more frequent and severe, releasing environmental hazards such as microcystin that pose potential threats to human and animal health. Autophagy has been shown to play a crucial role in regulating immune responses induced by environmental hazards, enabling cells to adapt to stress and protect against damage. Although microcystin-LR (MC-LR) has been identified to affect autophagy in mammalian, its impact on aquatic animals has been poorly studied. To investigate the toxicological effects of MC-LR in aquatic ecosystems, we constructed a microRNA profile of acute MC-LR stress in the hepatopancreas of the Chinese mitten crab. Interestingly, we found the MC-LR exposure activated autophagy in the hepatopancreas based on the following evidence. Specifically, mRNA expression level of ATG7, Beclin1 and Gabarap was significantly up-regulated, autophagy regulatory pathways were significantly enriched, and numerous autolysosomes and autophagosomes were observed. Additionally, we found that miR-282–5p and its target gene PIK3R1 played important regulatory roles in autophagy by in vivo and in vitro experiments. Overexpression of miR-282–5p mimicked MC-LR-induced autophagy by inhibiting PIK3R1 expression, while miR-282–5p silencing inhibited autophagy by promoting PIK3R1 expression. Altogether, our findings suggest that MC-LR increases miR-282–5p, which then targets inhibition of PIK3R1 to stimulate autophagy. This study focused on the stress response regulatory mechanisms of juvenile crabs to toxic pollutants in water, offering a potential target for alleviating the toxicity of MC-LR. These findings lay a foundation for reducing the toxicity of MC-LR and environmental hazards in organisms.

Population genomics provides evidence of interspecific hybridisation and population structure in the blue-swimmer crab (Portunus armatus) along the Western Australian coastline

Responsible and sustainable fisheries management requires a comprehensive knowledge of stock structure. Here, we examine population structure in the blue-swimmer crab (Portunus armatus), which supports one of the largest commercial and recreational fisheries within Western Australia (WA). Tissue samples from adult P. armatus were collected from 16 sites along the WA coastline from Albany to the Kimberley, a distance spanning over 3000 km. Adult individuals were also collected from one site in South Australia (SA) and one in the Northern Territory (NT), the latter separated into two morphologically similar species, P. armatus and P. pelagicus, as their ranges are known to overlap in northern Australia. Juvenile crabs were also sampled from five sites within the south-west region of WA to test for evidence of local recruitment. Using a panel of 11,175 single-nucleotide polymorphism (SNP) loci, we found evidence of two genetically distinct clusters in the NT sample and the northernmost WA site in the Kimberley region consistent with two sympatric species. We also found evidence of hybridisation between the two groups where they co-occur. Subsequent analyses on the remaining WA sites and SA, revealed the presence of four genetically distinct populations, represented by sites at SA, Exmouth, Shark Bay and the south-west region of WA. Additional analyses focussing on the south-west of WA exclusively failed to detect any appreciable population structure within this region. Consistent with this pattern, juveniles collected from five sites within south-west region of WA were no more genetically related to other juveniles from the same sampling site, on average, than juveniles collected elsewhere. Our results suggest the south-west region of WA is comprised of a single panmictic population, consistent with the view that populations along this coastline are highly interconnected due to inshore and offshore currents. Future management should consider a more integrated approach for managing blue-swimmer crab fisheries within the south west region of WA and improved monitoring in northern Australia, where two genetically distinct groups are currently fished as a single stock.

Assessment of treatment-specific tethering survival bias for the juvenile blue crab Callinectes sapidus in a simulated salt marsh.

The blue crab (Callinectes sapidus) is ecologically and economically important in Chesapeake Bay. Nursery habitats, such as seagrass beds, disproportionately contribute individuals to the adult segment of populations. Salt marshes dominated by smooth cordgrass Spartina alterniflora are intertidal nursery habitats which may serve as a refuge from predation for juvenile blue crabs. However, the effects of various characteristics of salt marshes on nursery metrics, such as survival, have not been quantified. Comparisons of juvenile survival between salt marshes and other habitats often employ tethering to assess survival. Although experimental bias when tethering juvenile prey is well recognized, the potential for habitat-specific bias in salt marshes has not been experimentally tested. Using short-term mesocosm predation experiments, we tested if tethering in simulated salt marsh habitats produces a habitat-specific bias. Juvenile crabs were tethered or un-tethered and randomly allocated to mesocosms at varying simulated shoot densities and unstructured sand. Tethering reduced survival, and its effect was not habitat specific, irrespective of shoot density, as evidenced by a non-significant interaction effect between tethering treatment and habitat. Thus, tethering juvenile blue crabs in salt marsh habitat did not produce treatment-specific bias relative to unvegetated habitat across a range of shoot densities; survival of tethered and un-tethered crabs was positively related to shoot density. These findings indicate that tethering is a useful method for assessing survival in salt marshes, as with other nursery habitats including seagrass beds, algae and unstructured sand.

Coupled patterns of natural and anthropogenic resources in typical ecosystems in coastal areas of China

The coastal area of Yancheng, China, is one of the hotspots for ecological research. Under the coupling of human and natural ecosystems, the region has gradually evolved into a coexistence of aquatic, agricultural and mudflat ecosystems. What are the patterns of natural and artificial resource inputs and patterns of change in ecosystems? How can ecological flows be analyzed at a uniform scale? Here, we selected six typical local ecosystems, namely, rice‒wheat for enterprises (RWE), rice‒wheat for smallholder households (RWS), chrysanthemum‒wheat (CW), fish polyculture (FP), juvenile crab farming (JF) and clam polyculture (CP), and analyzed their energy flow flux and sustainability based on emergy theory. The results showed that anthropogenic resource inputs were higher than natural resource inputs in all ecosystems, and the inputs of aquatic ecosystems were greater than those of agroecosystems. The greatest total input was 2.0 E+17 seJ/ha/yr for FP, and the lowest was 1.9 E+16 seJ/ha/yr for RWE. The proportions of renewable and artificial inputs for RWE, RWS, CW, FP, JF and CP were 32.8% vs. 96.1%, 40.3% vs. 96.5%, 34.7% vs. 97.0%, 32.6% vs. 99.4%, 55.1% vs. 98.5%, and 62.5% vs. 98.6%, respectively. The highest input to agroecosystems was nitrogen fertilizer, while in JF and CP, it was water, and feed (63.3%) accounted for the highest percentage of input in FP. JF and CP had lower environmental loads and higher sustainability than other ecosystems, but this still represents a high input compared to agroecosystems. Human-led resource coupling profoundly affects ecosystem sustainability, and various thresholds of energy use and ecological sustainability need to be studied in depth. Continuous exploration of methods and mechanisms for the maintenance and evolution of ecosystems with low total inputs and low inputs of non-renewable resources can contribute to high-quality sustainable development of an area or region.

Triacylglycerols are a Rich Source of Polyunsaturated Fatty Acids in Red King Crab Juveniles (Paralithodes camtschaticus)

Abstract: In the Sea of Japan and the Okhotsk Sea, the red king crab Paralithodes camtschaticus is the major commercial species of the crab. The crab is a rich source of polyunsaturated fatty acids (PUFAs). The composition of triacylglycerol (TG) molecular species in freshly collected juveniles of P. camtschaticus has been determined for the first time. By supercritical fluid chromatography with mass-spectrometry, 45 molecular species of TG were identified. Most of the molecular species contained docosahexaenoic acid (DHA; 22:6n-3), eicosapentaenoic acid (EPA; 20:5n-3), arachidonic acid (AA, 20:4n-6), and monounsaturated fatty acid 18:1. Thus, DHA, EPA, and AA received from the diet are used to build phospholipids (PL) and also stored in TG in P. camtschaticus juveniles. Therefore, the crab is a rich source of PUFAs, which are concentrated both in structural PL and in reserve TG.