Pubertal molt is a vital stage in the cultivation of mature female crabs in the aquacultural industry of Scylla paramamosain. Since fasting occurs during molting, which requires a large supply of energy, internal energy reserves are critical. However, the dynamics of energy supply during pubertal molt is not clear. This study focuses on the variations of carbohydrates and lipids in serum during the pubertal molt of S. paramamosain via a metabolomics approach. Eleven lipid or carbohydrate metabolic pathways were significantly influenced postmolt. A remarkable decrease in carbohydrates in serum suggested that free sugars were consumed for energy. A significant decrease in glucose and alpha-d-glucosamine 1-phosphate showed that chitin synthesis exhausted glycogen, resulting in insufficient glucose supply. An increase in l-carnitine and acetylcarnitine, and a significant decrease in 15 fatty acyls and 8 glycerophosphocholines in serum indicated that carnitine shuttle was stimulated, and β-oxidation was upregulated postmolt. In addition, astaxanthin, ponasterone A, and riboflavin in serum were significantly decreased postmolt. Eleven potential metabolite biomarkers were identified for pubertal molt. Taken together, carbohydrates and lipids were possibly major energy reserves in pubertal molt. This study suggests that an increase in carbohydrate and lipid levels in crab feed may alleviate the effects of fasting during molt and improve farm productivity in mature female crabs.

The crustacean hyperglycemic hormone (CHH) is a multifaceted neuropeptide instrumental in regulating carbohydrate and lipid metabolism, reproduction, osmoregulation, molting, and metamorphosis. Despite its significance, there is a dearth of research on its metabolic impact on the gills and epidermis—key organs in osmoregulation and molting processes. This study employed CHH dsRNA injections to silence CHH gene expression in Procambarus clarkii, followed by a metabolomic analysis of the gills and epidermis using nuclear magnetic resonance spectroscopy. Metabolic profiling through principal component analysis revealed the most pronounced changes at 24 h post-injection (hpi) in the epidermis and at 48 hpi in the gills. At 24 hpi, the epidermis exhibited significant modulation in 25 enrichment sets and 20 KEGG pathways, while at 48 hpi, 5 metabolite sets and 6 KEGG pathways were prominently regulated. Notably, pathways associated with amino acid metabolism, carbohydrate metabolism, and cofactor and vitamin metabolism were affected. A marked decrease in glucose and other carbohydrates suggested a compromised carbohydrate supply, whereas increased levels of citrate cycle intermediates implied a potential boost in energy provision. The silencing of CHH gene expression hampered the carbohydrate supply, which was possibly the main energy derived substrates. Conversely, the gills displayed significant alterations in 15 metabolite sets and 16 KEGG pathways at 48 hpi, with no significant changes at 24 hpi. These changes encompassed amino acid, carbohydrate, and lipid metabolism pathways. The decline in TCA cycle intermediates pointed to a potential downregulation of the cycle, whereas a decrease in ketone bodies indicated a shift towards lipid metabolism for energy production. Additionally, increased levels of nicotinate, nicotinamide, and quinolinate were observed in both organs. Overall, CHH’s impact on the epidermis was prominent at 24 hpi and diminished thereafter, whereas its influence on metabolism in gills was delayed but intensified at 48 hpi. This differential CHH effect between gills and epidermis in P. clarkii provides new insights into the organ-specific regulatory mechanisms of CHH on energy metabolism and osmoregulation, warranting further comparative studies to elucidate the distinct roles of CHH in these organs.

Background: Aquaculture increasingly seeks sustainable alternatives to fishmeal, a key protein source in fish diets. Black Soldier Fly Larvae (BSFL) meal is a promising substitute, but its effects on fish growth, immunity, and gut health need further investigation. This study aimed to evaluate the impact of varying BSFL inclusion levels on juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), a widely farmed species in tropical aquaculture. Methods: Juvenile hybrid grouper were fed diets with four levels of BSFL substitution (0%, 10%, 30%, and 50%) over 56 days. Key metrics such as growth performance, immune function, antioxidant capacity, and gut transcriptome were analyzed. Results: Replacing fish meal with BSFL meal had no significant effect on the survival rate of hybrid grouper (p > 0.05) but significantly affected growth performance, immune function, and antioxidant capacity (p < 0.05). BSFL10 and BSFL30 groups showed good growth and elevated immune enzyme activity, with significantly higher HIS levels (p < 0.05); the Wf of the BSFL10 group was comparable to the control. However, excessive replacement (BSFL50) led to reduced growth (Wf significantly lower, p < 0.05) and increased oxidative stress, as indicated by higher CAT activity (p < 0.05). Transcriptomic analysis revealed upregulation of immune- and metabolism-related genes with increasing BSFL levels, with immune pathways notably activated in the BSFL50 group. Conclusions: BSFL meal is a promising alternative to fishmeal in juvenile hybrid grouper diets, with moderate inclusion (10–30%) being most beneficial. Excessive BSFL substitution (50%) may impair fish health, highlighting the need for careful formulation in aquaculture diets.

The red-claw crayfish Cherax quadricarinatus has been widely introduced and cultured in China and has become a crucial economic freshwater species. However, individuals reared from the same batch of seedlings in uniform aquaculture systems exhibit significant size variation within and between genders, which notably impedes the optimization of both their quality and yield. Gut microbiota plays an important role in the metabolism, development, and immunity of aquatic animals. However, the knowledge on the intestinal microbiota of red-claw crayfish with various sizes and genders is poor. In this study, the intestinal microbiota of red-claw crayfish cultured in consistent farming conditions were separated to larger-sized female (GUBF), larger-sized male (GUBM), smaller-sized female (GUSF), and smaller-sized male (GUSM) groups based on their body size (weight) and gender, before being analyzed via high-throughput 16S rRNA gene sequencing. The intestinal microbiota results showed that alpha diversity tended to generally decrease in the order of GUBF, GUBM, GUSF, and GUSM, indicating that the richness and evenness of the gut flora were gradually improved with the increase in body weight or from male to female. Community richness and diversity were highest in the GUBF group, followed by the GUBM, GUSF, and GUSM groups, respectively. Beta diversity indicated significant differences in gut microbiota between the GUBF and GUSF, GUBM and GUSM, GUBF, and GUBM groups. Further analysis showed that the dominant phyla in the intestine of the red-claw crayfish were Firmicutes, Proteobacteria, Fusobacteriota, Bacteroidota, and Deinococcota, and the dominant genera were Vibrio, Tyzzerella, Candidatus Bacilloplasma, Citrobacter, and Candidatus Hepatoplasma. Moreover, nine phyla and 106 genera were identified to be significantly different in abundance among all four groups. Pairwise comparisons revealed that the phylum Dependentiae and Planctomycetota and genus Babeliaceae_unclassified were significantly abundant in the gut of female crayfishes, regardless of body size. On the other hand, irrespective of genders, the abundance of Novosphingobium, Piscinibacter, and Citrobacter was significantly increased or declined in the larger or smaller crayfishes, respectively. PICRUSt2 analysis based on the KEGG database suggested that the pathway bacterial secretion system, isoflavonoid biosynthesis, and pathway glycerolipid metabolism were significantly up- and down-regulated in female individuals, respectively, regardless of body sizes. Meanwhile, the adipocytokine signaling pathway, pyruvate metabolism, and pathway electron transfer carriers were significantly up- and down-regulated in larger individuals, respectively, regardless of gender. Gender differences may induce gut microbiota to exert a greater impact on hormonal regulation, whereas differences in individual size seem to lead gut microbiota to develop a preference for food intake and energy sources. In summary, this study revealed key differences in the intestinal microbiota of the crayfish with different sizes and genders, even in those which were cultured in the same environment and period, which potentially suggest that the intestinal microbiota may be influenced by some other factors in the culture system, such as hormone secretion, metabolism, and immunity. This study will contribute to improving growth performance and animal quality in the aquaculture of C. quadricarinatus.

The red-claw crayfish, Cherax quadricarinatus, is a commercially valuable freshwater aquaculture species, with muscle flavor representing a core trait driving consumer preference and market value. Under identical farming conditions, same-batch crayfish commonly develop marked size divergence within and between sexes, but the impacts of this variation on muscle volatile flavor profiles remain largely unexplored. Here, C. quadricarinatus reared under consistent environmental conditions were categorized into four groups by body weight and sex: large-size female (GUBF), large-size male (GUBM), small-size female (GUSF), and small-size male (GUSM). Headspace solid-phase microextraction–gas chromatography–mass spectrometry (HS-SPME/GC-MS) was employed to profile volatile organic compounds. Multivariate statistical analysis, relative odor activity value calculation, metabolic pathway and network analysis, and receiver operating characteristic (ROC) analysis were combined to dissect flavor variation patterns, identify key aroma compounds, reveal underlying metabolic mechanisms, and screen potential biomarkers. Proximate composition analysis showed significant size differences in crude protein, lipid, moisture, and meat yield, with no significant sex differences. One hundred thirty-six volatile metabolites across 15 chemical categories were identified in all samples. Multivariate statistical analyses revealed clear separation among the four groups, suggesting that both body size and sex shape muscle volatile metabolite profiles, with stronger effects observed in females. Thirty-eight shared aroma-active compounds were detected, mainly including alcohols, aldehydes, ketones, esters, and aromatic hydrocarbons. The overall sensory profile was dominated by sweet-like notes, followed by fruity and green notes. Sex-related flavor differences were relatively slight in large-size crayfish but pronounced in small-size individuals. Large-size female crayfish had simpler flavor composition, while small-size females showed higher diversity and abundance of flavor compounds; size variation had limited effects on male flavor. Butanoate metabolism was significantly enriched in both the small-size sex comparison and female size comparison. Core metabolic frameworks were generally conserved across groups, but key hub metabolites differed by comparison type. This study systematically characterized the volatile flavor profiles of C. quadricarinatus muscle across different body sizes and sexes under controlled farming conditions, providing preliminary references for quality evaluation and premium aquaculture optimization of C. quadricarinatus.