Background: Tropical stenothermal fish exhibit special tolerance and response to cold stress. However current knowledge of the molecular mechanisms response to cold stress in aquatic ectotherms is largely drawn from eurythermal or extreme stenothermal species. The tiger barb Puntius tetrazona is a tropical stenothermal fish, with great popularity in aquarium trade and research. Results: To investigate the response mechanism of P. tetrazona to low temperature, fish were exposed to increasing levels of acute cold stress. Histopathological analysis showed that the brain, gill, liver and muscle tissues appeared serious damage after cold stress (13 °C). Brain, gill, liver and muscle tissues from control (CTRL) groups (27 °C) and COLD stress groups (13 °C) of eight-month fish (gender-neutral) were sampled and assessed for transcriptomic profiling by high-throughput sequencing. 83.0 Gb of raw data were generated, filtered and assembled for de novo transcriptome assembly. According to the transcriptome reference, we obtained 392,878 transcripts and 238,878 unigenes, of which 89.29% of the latter were annotated. There were 23,743 differently expressed genes (DEGs) been filtered from four pairs of tissues (brain, gill, liver and muscle) between these cold stress and control groups. These DEGs were mainly involved in circadian entrainment, circadian rhythm, biosynthesis of steroid and fatty acid. There were 64 shared DEGs between the four pairs of groups, and five were related to ubiquitylation/deubiquitylation. Our results suggested that ubiquitin-mediated protein degradation might be necessary for tropical stenothermal fish coping with acute cold stress. Also, the significant cold-induced expression of heat shock 70 kDa protein (HSP70) and cold-induced RNA-binding protein (CIRBP) was verified. These results suggested that the expression of the molecular chaperones HSP70 and CIRBP in P. tetrazona might play a critical role in coping with acute cold stress. Conclusions: This is the first transcriptome analysis of P. tetrazona using RNA-Seq technology. Novel findings about tropical stenothermal fish under cold stress (such as HSP70 and CIRBP genes) are presented here. This study contributes new insights into the molecular mechanisms of tropical stenothermal species response to acute cold stress.

Over the past a few years, evidences indicate that adenosine triphosphate (ATP) is an energy source for the binding, maturation, assembly, and budding process of many enveloped viruses. Our previous studies suggest that the F1-ATP synthase beta subunit (ATPsyn β, BP53) of the shrimp Litopenaeus vannamei (L. vannamei) might serve as a potential receptor for white spot syndrome virus (WSSV)’s infection. BP53 was localized on the surface of shrimp hemocytes and gill epithelial cells by immunofluorescence assay and immunogold labeling technique. Cell surface ATP synthesis was demonstrated by an in vitro bioluminescent luciferase assay. Furthermore, the expression of bp53 after WSSV infection was investigated by RT-PCR test. In addition, RNAi was developed to knock down endogenous bp53. BP53 is present on shrimp cell surface of hemocytes and gill epithelia. The synthesized ATP was detectable in the extracellular supernatant by using a bioluminescence assay, and the production declined post WSSV binding and infection. Knocking down endogenous bp53 resulted in a 50% mortality of L. vannamei. These results suggested that BP53, presenting on cell surface, likely served as one of the receptors for WSSV infection in shrimp. Correspondingly, WSSV appears to disturb the host energy metabolism through interacting with host ATPsyn β during infection. This work firstly showed that host ATP production is required and consumed by the WSSV for binding and proceeds with infection process.

Goldfish are one of the most popular models for studying the genetic diversity of skin color. Transcriptome sequencing (RNA-seq) and whole genome bisulfate sequencing (WGBS) of skin tissues from the third filial (F3) cyan (CN), black (BK), and white (WH) goldfish were conducted to analyze the molecular mechanism of color transformation in fish. The RNA-seq yielded 56 Gb of clean data and 56,627 transcripts from nine skin samples. The DEGs (differentially expressed genes) were enriched in cell junction cellular components and the tight junction pathway. Ninety-five homologs of the claudin family were predicted and 16 claudins were identified in correlation with skin color transformation. WGBS yielded 1079 Gb of clean data from 15 samples. Both the DEGs and the DMRs (differentially methylated regions) in the BK_CN group were found to be enriched in cytoskeleton reorganization and vesicle trafficking. Masson staining and TEM (transmission electron microscopy) confirmed the varied distribution and processes of melanosome/melanin in skin tissues. Our results suggested that cytoskeleton reorganization, cell junction, and the vesicle trafficking system played key roles in the transfer of the melanosome/melanin, and it was the extracellular translocation rather than the biosynthesis or metabolism of the melanin process that resulted in the color transformation of cyan goldfish. The data will facilitate the understanding of the molecular mechanisms underlying dynamic skin color transformation in goldfish.

This study assessed whether fermented rapeseed meal (FRSM) could alleviate the negative impacts of rapeseed meal (RSM) on growth, intestinal health, and liver function in koi carp ( Cyprinus carpio ). Eighty‐one koi carp were randomly divided into three dietary groups: a control group receiving a soybean meal (SBM) diet, an unfermented RSM group, and a FRSM group. Growth performance, serum biochemical parameters, tissue histology, gut microbiota, and transcriptomic profiles were assessed. The findings showed that the RSM and FRSM groups had notably lower weight gain, weight gain rate, and specific growth rate (SGR) compared to the SBM group ( p < 0.05). In the RSM and FRSM groups, serum antioxidant enzyme activities (SOD, CAT, and GSH‐PX) significantly decreased, whereas MDA levels and AST activity significantly increased ( p < 0.001). Histological analysis revealed that intestinal villus structures remained intact in all groups, but the FRSM group exhibited a significant reduction in crypt depth ( p = 0.019). Scanning electron microscopy (SEM) showed that the SBM group had a greater microvilli density than the RSM and FRSM groups. Severe hepatic pathological changes were observed in the RSM group, whereas hepatic damage was notably alleviated in the FRSM group. LEfSe analysis identified the Ruminococcus torques group as a distinctive biomarker in the FRSM group, showing significant enrichment relative to both the SBM and RSM groups. RSM induced significant transcriptomic alterations in the intestine and liver, characterized by increased oxidative stress, metabolic dysfunction, and activation of inflammatory pathways. FRSM transformed these responses by enhancing autophagy, lipid metabolism, and cellular repair mechanisms, indicating a protective and regenerative effect. Quantitative PCR analysis validated the expression trends detected in the omics. In conclusion, dietary supplementation with FRSM may alleviate intestinal and hepatic injuries induced by high‐level RSM inclusion, potentially through gut–liver axis modulation, enrichment of Ruminococcus torques group , and activation of autophagy‐related pathways.