Background: Largemouth bass ( Micropterus salmoides ) is among the most economically important freshwater fish species. High temperature is a major abiotic stressor, leading to increased mortality and significant economic losses. However, research on the regulatory mechanisms of heat stress response in largemouth bass is limited. This study aims to elucidate the mechanisms of adaptability in largemouth bass during heat stress and subsequent recovery. Results: The morphobiochemical alterations and adaptive mechanisms induced by high water temperature in the gill, brain and liver tissues of largemouth bass are investigated through biochemical blood analysis, haematoxylin and eosin staining, transmission electron microscopy and transcriptomic and proteomic profiles. The results reveal that heat stress-induced oxidative stress causes severe damage to the gill, brain and liver tissues, as well as to the mitochondria, endoplasmic reticulum and Golgi apparatus of these tissues. Such damage is alleviated during the recovery stage, which is closely associated with the PPAR signalling pathway, focal adhesion, ErbB signalling pathway, retinoid metabolism, and cytochrome P450 pathways. These pathways contribute to damage repair, functional recovery, and maintenance of homeostasis after heat stress. Furthermore, experimental validation reveals the pivotal role of Hspa9 in the heat stress response. Conclusions: These findings reveal that oxidative stress induced by heat stress can severely damage critical tissues in largemouth bass, but the tissues are heterogeneous and have complex and flexible heat stress response regulatory mechanisms. Furthermore, Hspa9 plays an important protective role in the process of heat stress.

The giant freshwater prawn (Macrobrachium rosenbergii, GFP) is a highly valuable crustacean species in global aquaculture. However, a social hierarchy exists among the distinct male morphotypes, specifically blue-clawed males (BC), orange-clawed males (OC), and small males (SMs). In this study, to identify the specific metabolites among BC, OC, and SM, hemolymph samples were collected for the untargeted liquid chromatography–mass spectrometry metabolomics (LC–MS). A total of 172, 546, and 578 significantly different metabolites (SDMs) were identified in OC vs. BC, SM vs. BC, and SM vs. OC, respectively. Notably, creatine and glutamate in BC males likely enhance their aggressive behavior through improved energy metabolism. In the SM group, the up-regulation of prostaglandin E3, testosterone, and arachidonic acid may lead to premature gonadal maturation and enhance immunity. Serotonin, Glu-Pro, and pentanoylcarnitine detected in OC males reflect their physiological need for rapid growth and adaptation to social behaviors. In the SM group, the up-regulation of prostaglandin E3, arachidonic acid, and testosterone may promote premature gonadal maturation and enhance immunodominance. These findings will enhance the understanding of the physiological basis of social hierarchy formation in male GFPs from a metabolomics perspective.

This study investigated the effects of culture systems and feed types on the gut microbiota of mandarin fish (Siniperca chuatsi), using three production culture modes: pond–live bait (CE), pond–artificial feed (CS), and RAS–artificial feed (GS). Under identical pond culture conditions, CS fish fed compound feed had higher relative abundances of carbohydrate-metabolizing Bacteroidota and Firmicutes than CE. The CS group showed higher α-diversity, but β-diversity analysis indicated no significant community difference (p = 0.36), demonstrating that feed replacement only induced mild microbial shifts. LEfSe analysis uncovered 17 differential taxa: homeostasis-related genera enriched in CS, while the lipid-adapted Macellibacteroides prevailed in CE. Under identical artificial feed conditions, switching culture mode from pond (CS) to industrial RAS (GS) drastically reduced gut microbial diversity and simplified community structure. GS exhibited a sharp rise in Fusobacteriota, with Cetobacterium (64.94%) becoming the single dominant genus. α-diversity was lower in GS than CS, and β-diversity confirmed highly distinct community profiles between the two groups (p = 0.004). LEfSe detected 43 differential taxa with diverse metabolic genera abundant in CS. No PICRUSt2-inferred KEGG pathways remained significant after FDR correction in the above two comparison groups, so these functional trends are only for reference.

Rice–crab coculture, as China’s third-largest integrated farming model, is pivotal for sustainable Chinese mitten crab aquaculture. This study conducted untargeted metabolomics and 16S rRNA gene sequencing on gut contents of crabs from rice fields and ponds, integrating metabolic and microbial profiles. We aimed to reveal the chemical traits of rice-field Chinese mitten crab linked to gut microbiota, providing scientific guidance for optimizing culture practices and developing microbial additives. Both groups were dominated by the phyla Firmicutes, Proteobacteria, and Bacteroidota, but the phylum Bdellovibrionota was not detected in group R. A total of 1271 distinct amplicon sequence variants (ASVs) were identified, which were annotated to 649 genera. At the ASV level, the Chao1 index for the R group (197.12 ± 17.88) was notably lower compared to the P group (288.75 ± 30.59) (p < 0.01). In contrast, the Shannon index for the R group (3.90 ± 0.06) was significantly greater than that of the P group (3.70 ± 0.06) (p < 0.01). The PCA plot demonstrated a distinct discrimination between the groups. The P group had more microbial species but was dominated by Candidatus_Bacilloplasma, resulting in uneven distribution. In contrast, the R group had fewer species but a more balanced distribution. Among 3531 metabolites identified in both groups, 865 differed significantly. Compared to P, 736 metabolites were significantly upregulated and 129 were significantly downregulated in R. Key metabolic pathways included amino acid, carbohydrate, cofactor and vitamin metabolism, signaling, and xenobiotics biodegradation. Group R had higher levels of L-leucine, L-phenylalanine, L-tyrosine, 2-amino-1-phenylethanol, choline, and pyrophaeophorbide a, which correlated with genera like Candidatus_Hepatoplasma and Aeromonas (p < 0.05), suggesting better nutritional value, flavor, and metabolic health in rice-field crabs.