The Class II myosin light chain (myl) genes in Chinese perch (Siniperca chuatsi) have not yet been systematically characterised, and relationships with muscle fibre specification, development, and injury-associated remodelling remain unclear. In this study, fast and slow muscle fibres were initially distinguished using myofibrillar ATPase histochemistry. Subsequently, genome-wide mining identified 16 Class II myl genes, comprising eight essential and eight regulatory light-chain subunits. Their conserved-domain features, chromosomal distribution, phylogenetic relationships and expression profiles were analysed. Transcriptomic profiling showed that summed myl transcript abundance was higher in fast muscle than in slow muscle, accounting for 67.2% of the pooled myl transcript pool across the two muscle types (paired t-test, raw P = 0.036). mylpfa, myl1 and mylz3 were the major fast-muscle-associated genes, whereas myl10, myl2b and myl13 were preferentially expressed in slow muscle at the transcript level. These patterns support these genes as candidate fibre-type-associated expression markers. Developmental profiling identified stage-associated myl expression patterns, including a possible expression shift between mylpfb and mylpfa. In the descriptive injury-repair time course (d0-d7), FPKM profiles indicated that fast-muscle-associated genes (mylpfa, mylz3 and myl1) were lower at d1 and recovered by d3, whereas several slow-muscle-associated genes showed biphasic transcript-level increases. The slow-muscle-associated RLC gene mylpfb showed a delayed expression peak at d7. Notably, the embryonic isoform myl6l showed a modest increase from approximately 2 FPKM at d0 to 4-5 FPKM after injury, suggesting a possible injury-associated expression pattern that requires further validation. Together, these findings provide a genome-wide description of the Chinese perch myl gene family and identify candidate fibre-type-associated genes and descriptive injury-associated isoform expression patterns.

The Chinese soft-shelled turtle (Pelodiscus sinensis) is a high-value economically cultured aquatic species in China, and bacterial furunculosis severely restricts the sustainable development of its aquaculture industry. Proteus vulgaris, a ubiquitous opportunistic aquatic pathogen, can induce lethal systemic infections in aquatic animals under intensive culture conditions. However, the molecular mechanisms underlying P. vulgaris pathogenicity in P. sinensis, especially its regulatory effects on host circadian immune and antioxidant homeostasis, remain poorly elucidated. In the present study, a virulent P. vulgaris strain Lb18-01 was isolated from diseased P. sinensis with typical furunculosis symptoms. Artificial infection assays, median lethal dose (LD50) determination, serum biochemical and immune-antioxidant parameter detection, and 24 h rhythmic expression profiling of hepatic clock, immune and antioxidant genes were performed to clarify the pathogenic mechanisms of strain Lb18-01. The infection tests verified the strong virulence of Lb18-01, with 48 h and 96 h LD50 values of 1.0 × 106 CFU/g and 8.4 × 105 CFU/g, respectively, showing a time-dependent decline. P. vulgaris Lb18-01 infection significantly increased serum globulin, aminotransferase, alkaline phosphatase, acid phosphatase, myeloperoxidase and malondialdehyde levels, while markedly inhibiting serum total antioxidant capacity, which indicated severe inflammatory response, oxidative stress and hepatic tissue damage in infected turtles. Quantitative real-time PCR (RT-qPCR) analysis demonstrated that Lb18-01 infection dramatically disrupted the circadian rhythmic expression of core clock genes (CLOCK, Bmal1, Per) and key immune-antioxidant genes (IL-6, Nrf2, HMOX1, CAT) in the liver of P. sinensis, characterized by altered rhythmic parameters, significant phase shifts and abolished endogenous rhythmicity. Genomic analysis revealed that Lb18-01 possesses a circular genome of 4,139,074 bp with a GC content of 39.66%, encoding 4281 protein-coding genes, 78 virulence factors and 92 antibiotic resistance genes including efflux pump and aminoglycoside resistance determinants. Comparative genomic analysis with five reference P. vulgaris strains (ATCC 49132, CSUR P1867, CSUR P1868, FDAARGOS 366, FDAARGOS 556) showed 84%–99% sequence identity, whereas mobile genetic element-mediated chromosomal inversions, rearrangements and insertions/deletions resulted in incomplete genomic collinearity. Collectively, P. vulgaris Lb18-01 is a highly pathogenic strain that induces systemic tissue injury in P. sinensis via disrupting host circadian, immune and antioxidant homeostasis, and harbors abundant virulence and antibiotic resistance genetic determinants. These findings enrich the understanding of P. vulgaris pathogenicity in reptilian hosts and provide novel insights for the targeted prevention and control of turtle furunculosis.

Global temperature fluctuations exert multifaceted adverse effects on aquaculture, particularly through seasonal high- and low-temperature stress. Creatine serves to enhance growth performance, stimulate muscle fiber development, and reduce fat deposition. The present study evaluated the effects of dietary creatine on growth performance, muscle quality, and hepatic lipid metabolism in largemouth bass (Micropterus salmoides) under chronic temperature stress in East China ponds. Fish were fed diets containing 0.25% (CT1/CO) or 0.5% (CT2/CM) creatine under summer chronic heat stress (30.6 to 35.7°C) and winter chronic cold stress (20.3 to 7.4°C), respectively. Under summer chronic heat stress, creatine did not significantly influence growth or improved hepatic lipid metabolism. In the creatine-treated group, muscle hardness increased significantly, which was associated with reduced myofiber diameter and increased myofiber density, independent of collagen content. Creatine promoted myofiber proliferation, as indicated by upregulation of myod1 expression. Concurrently, it suppressed the expression of protein synthesis-related genes (s6k, eif3f) and upregulated muscular atrophy gene (foxo1a), collectively impeding myofiber hypertrophy. Under winter chronic cold stress, creatine-fed fish obtained significantly higher body weight, which is attributed to an increase of mesenteric fat. Hepatic lipid content, and total cholesterol (TC) levels were reduced, while serum triglycerides (TG) and TC levels increased in the creatine-treated group. The down-regulation of hepatic accα expression and up-regulation of atgl attenuated lipid deposition. The regulation of muscle by creatine is similar to that under summer heat stress. Combining comparisons under seasonal temperature stresses, active lipid catabolism resulted in better lipid-lowering effects of creatine under winter cold stress, while the increase in protein catabolism led to the disappearance of creatine effect on promoting myofiber hypertrophy under different seasonal temperature stresses. The present study elucidates the regulatory role of creatine under heat stress in summer and cold stress in winter, particularly in growth performance, lipid metabolism, and muscle texture, thereby providing insights for its appropriate application in aquaculture.

Fish skeletal muscle is a vital protein source for humans and exhibits continuous muscle fiber hypertrophy and hyperplasia during post-embryo development, yet the regulatory mechanisms governing its development remain poorly understood. Identifying candidate genes involved in skeletal muscle development and understanding the molecular mechanisms regulating this process can unlock new strategies for enhancing aquaculture productivity and quality. In this study, morphological and histological analyses of Megalobrama amblycephala at 14 developmental stages revealed that 30 d and 45 d post-fertilization are critical stages for fiber hyperplasia and hypertrophy, respectively. Leveraging single-cell RNA sequencing (scRNA-seq), we constructed a high-resolution cellular atlas of skeletal muscle, uncovering 13 distinct cell types and 51 candidate genes essential for M. amblycephala myogenesis. Notably, we discovered novel myoblast markers (trim109, pabpc4, and tcea3) through in situ hybridization and uncovered Igf2b-Igf1ra and Igf1-Igf1ra signaling pathways drive mesenchymal stem cell (MSC) differentiation into myogenic lineages. These findings establish the first comprehensive single-cell atlas of skeletal muscle development in M. amblycephala, delineating cell type-specific gene expression profiles and regulatory networks. This work not only advances the mechanism of teleost myogenesis but also provides valuable molecular targets for marker-assisted breeding programs aimed to enhance muscle production in commercially valuable aquaculture species.

Skeletal muscle growth is closely linked to glucose and lipid metabolism. However, the specific molecular mechanisms coordinating these processes remain poorly understood. In this study, two phenotypic groups, designated as "thin" and "fat", were selected from a single cultured population of largemouth bass (Micropterus salmoides). Histologically, lipid droplets within muscle fibers were more abundant in the fat group than in the thin group, and the average diameter of muscle fibers was smaller in the fat group. Transcriptome analysis of these groups revealed pyruvate dehydrogenase kinase 2 (Pdk2) as a potential regulatory factor governing both glucose and lipid metabolism and muscle fiber growth. In vivo, siRNA-mediated inhibition of Pdk2 upregulated lipogenic genes in fast muscle, leading to increased triacylglycerol accumulation without altering total cholesterol levels, validating its function. Histological analysis indicated that Pdk2 knockdown enhanced glycogen deposition in fast muscle fibers, correlating with the upregulation of glycogen synthesis-related genes. Moreover, the number of fibers with diameter < 20 mu m was significantly increased, indicating an enhancement in muscle fiber hyperplasia. This effect was attributed to enhanced proliferation and differentiation of myoblasts, as evidenced by the increase in the abundance of bromodeoxyuridine-labeled cells and expression of Myf5, MyoD, and MyoG. Collectively, the study suggests that Pdk2 may play a critical role in promoting glucose and lipid metabolism while negatively regulating myoblast proliferation. These findings not only enhance our understanding of the interplay between energy metabolism and myoblast proliferation during the growth of largemouth bass but also provide a potential molecular target for genetic improvement relevant for aquaculture.

Twist2 plays a pivotal regulatory role in the growth of skeletal muscle across various organisms. Nonetheless, the specific mechanism by which Twist2 governs skeletal muscle function in fish, particularly in the economically significant Chinese perch (Siniperca chuatsi), remains unclear. Within the muscle injury model in Chinese perch, we observed that Twist2 expression was upregulated during the repair phase of fast muscle tissue, exhibiting an expression pattern analogous to that of Pax7. Following the knockdown of Twist2 using Twist2-specific in vivo-siRNA in fast muscle tissues, the expression of myogenic regulatory factors (MRFs) and Myomaker was significantly reduced in the Twist2-siRNA-treated group compared with the control group, whereas no significant differences were observed for Pax3 and Pax7. Furthermore, the diameter of myofibers and the number of nuclei in single myofibers were reduced, and concurrently, the number of BrdU-positive cells (proliferating cells) was significantly reduced in the Twist2-siRNA-treated group. Taken together, this study demonstrates that Twist2 promotes myoblast proliferation and fusion, thereby regulating fast muscle growth in juvenile Chinese perch. These findings provide a clear direction for further exploration of molecular mechanisms underlying skeletal muscle growth in economic fish species.

Fish skeletal muscle serves as a crucial source of high-quality protein for human consumption. MicroRNAs (miRNAs) are important epigenetic regulators for the growth and development of skeletal muscle. Although the functions of many myogenic miRNAs have been studied, the regulatory functions of miRNAs in fish skeletal muscle have not been fully investigated. Here we show miR-125b is highly expressed in fast muscle of Chinese perch (Siniperca chuatsi) at 30-60 days post-hatching (dph), with transient downregulation during the skeletal muscle injury repair stage, implying its essential regulatory role in fast muscle growth and injury repair. Moreover, inhibiting miR-125b in Chinese perch resulted in an increase in muscle fiber diameter, the number of proliferating myoblasts and nuclei in single muscle fiber. In contrast, overexpression of miR-125b in Chinese perch led to a significant reduction in muscle fiber diameter, accompanied by a significant decrease in the number of proliferating myoblasts and the number of nuclei in single muscle fiber. Bioinformatics analysis and dual luciferase assays confirmed MyoD and Myomaker as direct targets of miR-125b. In summary, our findings demonstrate that miR-125b modulates the expression of MyoD and Myomaker, thereby regulating the proliferation and fusion of myoblasts, and ultimately controlling the hypertrophy of muscle fibers in Chinese perch. This finding holds significant relevance in unraveling the genetic mechanisms that govern the developmental traits of muscle fibers in fish during the postembryonic phase.

Large yellow croaker is one of the most popular economic fish species in China. There are studies on the effects of salinity on the growth and development of large yellow croaker (Larimichthys crocea), but the effects of the hypothalamic-pituitary-interrenal axis (HPI), HPI axis-related genes, and immune-related gene expression and its mechanisms have not been reported. This study analyzed the comparative transcriptomics of brain tissue in large yellow croaker under different salinity (12, 24, and 36 ppt) treatments for 4 weeks. The results showed that there were 1568 differential expression genes in the high salinity (HB) and normal salinity (NB) groups, including 494 up-regulated and 1074 down-regulated transcripts, and 1720 differential expression genes in the low salinity (LB) and normal salinity (NB) groups, including 486 up-regulated and 1234 down-regulated transcripts. Some pathways were significantly enriched, including the adrenergic signaling pathway of cardiomyocytes, oxidative phosphorylation, aldosterone synthesis and secretion, chemokine signaling pathway, and cyclic adenosine monophosphate (cAMP) signaling pathway. Quantitative Real-time polymerase chain reaction (qPCR) analysis further confirmed changes in the expression levels of HPI axis-related genes (β2-ADR, GH, and PRL) and significant changes in the expression levels of immune-related genes (IL6st, IL6, CXCL12, CD40, IFNAR1, SOCS2, SOCS6, and IRF1). In summary, this experiment demonstrates that salinity stress can activate the HPI axis and influence its immune function in large yellow croaker. Furthermore, the expression of immune factors during the immune response is regulated by the upstream genes of the HPI axis. The findings of this study are significant for understanding the physiological and immune responses of large yellow croaker to salinity stress.

As one of the structural tissues of fish skeletal muscles, slow muscle plays an important role in physiological and metabolic activities. The Hedgehog (Hh) signaling pathway has been reported to be involved in regulating the development and metabolism of slow muscle in fish. The underlying molecular mechanisms by which the Hedgehog (Hh) signaling pathway governs metabolic homeostasis within the slow muscle tissue of fish remain an enigma. In order to reveal the functional regulatory role of the Hh signaling pathway in the slow muscle of Chinese perch (Siniperca chuatsi), Cyclopamine was used to inhibit the Hh signaling pathway and Illumina sequencing technology was employed to explore the effect of inhibiting the Hh signaling pathway on slow muscle transcriptomes. In this study, a total of 666 differentially expressed genes (DEGs) were obtained between the control and Cyclopamine-treated groups. Functional enrichment analyses showed that the DEGs are mainly enriched in signaling pathways related to autophagy and metabolism, such as the mTOR signaling pathway, the autophagy pathway and the FoxO signaling pathway. The Western blotting analysis showed that the autophagy levels increased after treatment with Cyclopamine. Transmission electron microscopy results showed that the number of autophagic lysosomes was reduced in the Cyclopamine-treated group. The above results suggest that the Hh signaling pathway may play a key role in the regulation of autophagy and metabolism in slow muscle of Chinese perch, thus ensuring normal physiological activities in their muscles. In addition, the present study provides a direction for further elucidating the role of Hh signaling pathway in regulating the dynamic balance of metabolism in the slow muscle of Chinese perch.

High-fat diet (HFD) affects flesh quality in fish, but the dynamic changes in flesh nutritional composition and texture parameters have not been comprehensively studied. In this study, six replicates of thirty Nile tilapia (Oreochromis niloticus) weighing 5.5 +/- 0.3 g were fed a medium-fat diet (MFD, 6 % fat) or a HFD (12 % fat) for eight weeks. The results showed that feeding the fish on HFD increased body weight and lowered feed intake than those fed on MFD. However, the fish fed on MFD had significantly higher phospholipids (PL), phosphatidyl choline (PC) and phosphatidylethanolamine (PE) contents in muscle than those fed on HFD, primarily during sixth and eighth weeks. The fish fed on HFD accumulated more n-6 polyunsaturated fatty acids (PUFAs) in muscle, meanwhile fewer n-3 PUFAs as feeding continued. The amino acids changed mainly from the sixth week, when HFD feeding generally reduced essential amino acids (EAA) and half essential amino acids (HEAA) contents in muscle. The fish fed on HFD up-regulated the genes related to enhanced fiber hypertrophy such as myogenin (MyoG) and myogenic factor 6 (myf6) than those fed on MFD during the second and fourth weeks. Consequently, this led to reduced muscle fiber density and flesh hardness in fish fed on HFD from the sixth to eight weeks. Altogether, our study indicates that the nutritional composition and flesh texture parameters are modified during HFD feeding in Nile tilapia at different time points such that the regulation of each parameter has a distinct "time window".

The fusion of myoblasts is a crucial stage in the growth and development of skeletal muscle. Myomaker is an important myoblast fusion factor that plays a crucial role in regulating myoblast fusion. However, the function of Myomaker in economic fish during posthatching has been poorly studied. In this study, we found that the expression of Myomaker in the fast muscle of Chinese perch (Siniperca chuatsi) was higher than that in other tissues. To determine the function of Myomaker in fast muscle, Myomaker-siRNA was used to knockdown Myomaker in Chinese perch and the effect on muscle growth was determined. The results showed that the growth of Chinese perch was significantly decreased in the Myomaker-siRNA group. Furthermore, both the diameter of muscle fibers and the number of nuclei in single muscle fibers were significantly reduced in the Myomaker-siRNA group, whereas there was no significant difference in the number of BrdU-positive cells (proliferating cells) between the control and the Myomaker-siRNA groups. Together, these findings indicate that Myomaker may regulate growth of fast muscle in Chinese perch juveniles by promoting myoblast fusion rather than proliferation.

Fish exhibit indeterminate growth by recruiting new muscle fibers (hyperplasia) and increasing the size of already existing fibers (hypertrophy) to promote muscle growth. However, the molecular mechanism by which muscle fibers maintain hyperplasia and hypertrophy during the posthatching period in fish remains unclear. microRNAs have been reported to participate in the proliferation and differentiation of myoblasts in fish. In this study, we found that overexpression of miR-214 in Chinese perch (Siniperca chuatsi) by injecting agomiR-214 in vivo resulted in an increase in the diameter of myofibers, the number of satellite cells and proliferating myoblasts as well as the expression of Pax7, Myomaker and myogenic regulatory factors. However, inhibiting miR-214 by injecting antagomiR-214 in vivo significantly decreased the diameter of myofibers, the number of proliferating myoblasts and the expression of Myf5 and MyoD. In addition, inhibition of the Hedgehog pathway showed results similar to those of inhibition of miR-214. The in silico analysis and dual luciferase reporter assay revealed that Sufu, a negative regulator of the Hedgehog (Hh) signaling pathway, is a direct target of miR-214. Taken together, our results reveal that miR-214 induces the activation of satellite cells by regulating Hh signaling activity, and subsequently stimulates the proliferation, differentiation and fusion of myoblast, thus promoting hyperplasia and hypertrophy of skeletal muscle in Chinese perch.

Bioactive peptides have rich nutritional value and multiple biological functions, which plays a crucial role in health of aquatic animals. In this study, we screened crayfish shell bioactive peptides based on molecular simulation, and analyzed their effects on oxidative stress and lipid metabolism disorders induced by excessive copper (Cu) diet in zebrafish. The protein hydrolysates were prepared by enzymatic hydrolysis of crayfish shell protein using trypsin, and the peptide sequences were determined by LC-MS/MS. The peptide LPLWPY (LY-6, the molecular weight is 787.94 Da) identified using peptide database PeptideRanker prediction and molecular docking showed strong antioxidant potential. In vivo experiments of zebrafish showed that dietary supplementation of LY-6 peptide significantly improved the adverse effects of oxidative stress and abnormal lipid metabolism caused by excessive Cu diet. The results of zebrafish primary hepatocytes revealed that LY-6 peptide promoted the antioxidant capacity and lipid metabolism normalization of cells by regulating nrf2 and ppar gamma signaling pathways, thereby reducing oxidative stress and lipid accumulation. The findings of this study revealed that antioxidant peptide LPLWPY with strong from crayfish shell protein hydrolysates could alleviate oxidative stress and lipid metabolism abnormalities caused by excessive Cu diet in zebrafish, thus could be recommended as a potential functional feed ingredient for fish nutrition. It provides theoretical basis and reference for aquatic animal nutrition regulation and development of novel feed additives.

Siniperca species are highly valued freshwater fishes in China. In 2022, the country’s production of farmed Siniperca reached 401 kilotons. With the growing demand for high-quality aquatic products, Siniperca aquaculture offers major economic benefits and promising development prospects. However, the current reliance on live bait in Siniperca farming has resulted in resource wastage, environmental pollution, and disease outbreaks, hindering the healthy and sustainable growth of the industry. This review aims to comprehensively summarize the nutritional requirements of Siniperca in artificial farming, with a focus on proteins, amino acids, lipids, fatty acids, carbohydrates, and micronutrients. We also summarize the progress made in researching alternative protein and lipid sources, feed additives, and the development of artificially formulated feeds to replace live bait. The findings of this review will serve as a reference for further research on the nutritional requirements and development of formulated feeds for Siniperca aquaculture.

研究从鳜(Siniperca chuatsi)基因组中获得Shh(Sonic hedgehog)基因序列,对该基因编码的蛋白质和同源进化特征进行了分析.鳜Shh基因的开放阅读框(ORF)为1242 bp,编码413个氨基酸,分子量为46.01 kD,等电点(pI)为6.57,脂溶系数为82.83,亲水性平均系数为-0.292,拥有一个跨膜区,被推定为亲水性膜结合蛋白.Shh蛋白具有两个结构域,即Hh-N和Hh-C结构域.鳜Shh蛋白与自身所属的鲈形目鱼类Shh蛋白同源性较高.通过实时荧光定量PCR技术检测了鳜Shh基因的时空表达水平.结果显示:Shh的表达量在神经胚期表达显著上调,并在胚胎发育中后阶段保持较高水平.Shh在鳜不同组织中存在一定的表达差异,在脑、肠道中表达量较高,而在红肌、白肌等组织中表达量相对较低.通过环巴胺(Cyclopamine)处理鳜胚胎来抑制Shh信号通路的实验表明,Shh信号通路被抑制后,Pax3、Pax7、Myomaker、生肌调节因子及肌球蛋白重、轻链等基因的表达均显著降低,推测Shh参与调控鳜肌细胞的早期分化和发育过程.研究将有助于从分子水平了解Shh信号调控鱼类发育的分子机理,为鱼类发育生物学以及健康养殖提供参考依据.

Physiology disorders of the liver, as it is an important tissue in lipid metabolism, can cause fatty liver disease. The mechanism might be regulated by 17 circadian clock genes and 18 fat metabolism genes, together with a high-fat diet (HFD). Due to their rich nutritional and medicinal value, Chinese soft-shelled turtles (Trionyx sinensis) are very popular among the Chinese people. In the study, we aimed to investigate the influence of an HFD on the daily expression of both the core clock genes and the lipid metabolism genes in the liver tissue of the turtles. The two diets were formulated with 7.98% lipid (the CON group) and 13.86% lipid (the HFD group) to feed 180 juvenile turtles, which were randomly divided into two groups with three replicates per group and 30 turtles in each replicate for six weeks, and the diet experiment was administrated with a photophase regimen of a 24 h light/dark (12L:12D) cycle. At the end of the experiment, the liver tissue samples were collected from nine turtles per group every 3 h (zeitgeber time: ZT 0, 3, 6, 9, 12, 15, 18, 21 and 24) for 24 h to investigate the daily expression and correlation analysis of these genes. The results showed that 11 core clock genes [i.e., circadian locomotor output cycles kaput (Clock), brain and muscle arnt-like protein 1 and 2 (Bmal1/2), timeless (Tim), cryptochrome 1 (Cry2), period2 (Per2), nuclear factor IL-3 gene (Nfil3), nuclear receptor subfamily 1, treatment D, member 1 and 2 (Nr1d1/2) and retinoic acid related orphan receptor α/β/γ β and γ (Rorβ/γ)] exhibited circadian oscillation, but 6 genes did not, including neuronal PAS domain protein 2 (Npas2), Per1, Cry1, basic helix-loop-helix family, member E40 (Bhlhe40), Rorα and D-binding protein (Dbp), and 16 lipid metabolism genes including fatty acid synthase (Fas), diacylglycerol acyltransferase 1 (Dgat1), 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), Low-density lipoprotein receptor-related protein 1-like (Ldlr1), Lipin 1 (Lipin1), Carnitine palmitoyltransferase 1A (Cpt1a), Peroxisome proliferator activation receptor α, β and γ (Pparα/β/γ), Sirtuin 1 (Sirt1), Apoa (Apoa1), Apolipoprotein B (Apob), Pyruvate Dehydrogenase kinase 4 (Pdk4), Acyl-CoA synthase long-chain1 (Acsl1), Liver X receptors α (Lxrα) and Retinoid X receptor, α (Rxra) also demonstrated circadian oscillations, but 2 genes did not, Scd and Acaca, in the liver tissues of the CON group. However, in the HFD group, the circadian rhythms’ expressional patterns were disrupted for the eight core clock genes, Clock, Cry2, Per2, Nfil3, Nr1d1/2 and Rorβ/γ, and the peak expression of Bmal1/2 and Tim showed delayed or advanced phases. Furthermore, four genes (Cry1, Per1, Dbp and Rorα) displayed no diurnal rhythm in the CON group; instead, significant circadian rhythms appeared in the HFD group. Meanwhile, the HFD disrupted the circadian rhythm expressions of seven fat metabolism genes (Fas, Cpt1a, Sirt1, Apoa1, Apob, Pdk4 and Acsl1). Meanwhile, the other nine genes in the HFD group also showed advanced or delayed expression peaks compared to the CON group. Most importantly of all, there were remarkably positive or negative correlations between the core clock genes and the lipid metabolism genes, and their correlation relationships were altered by the HFD. To sum up, circadian rhythm alterations of the core clock genes and the lipid metabolism genes were induced by the high-fat diet (HFD) in the liver tissues of T. sinensis. This result provides experimental and theoretical data for the mass breeding and production of T. sinensis in our country.

Cadmium (Cd) is a toxic heavy metal pollutant in the environment. Excessive Cd in water has toxic effects on fish, endangering their healthy growth and ultimately affecting the quality and safety of aquatic products. To evaluate the toxicity of excessive Cd to fish through potential oxidative damage, Siniperca chuatsi was exposed to Cd in water for 15 days. It was found that Cd exposure significantly decreased the survival rate of S. chuatsi and Cd was detected in their muscle. Meanwhile, Cd disrupts the redox balance by reducing antioxidant enzyme activities, increasing reactive oxygen species (ROS) and malondialdehyde (MDA) levels in muscle, and promoting oxidative damage. Histomorphology showed that enlargement of muscle fiber gaps, cell swelling and vacuolar degeneration after Cd exposure. In addition, Cd toxicity induced up-regulating the expression of miR-216a, while down-regulation of Nrf2 protein and its downstream antioxidant enzyme genes expression. Further analysis revealed that miR-216a was significantly negatively correlated with the expression of Nrf2, and injection of miR-216a antagomir significantly enhanced the expression of Nrf2 and antioxidant enzyme genes, as well as the activity of antioxidant enzymes, thereby reducing the damage of Cd to fish. These results suggested that miR-216a-mediated Nrf2 signaling pathway plays an important role in Cd-induced oxidative stress of S. chuatsi muscle.

Objective:The PCSPHs were prepared by enzymatic hydrolysis of Procambarus clarkii shells,and their hypoglycemic and lipid-lowering activities in vitro were evaluated and peptide sequence were analyzed.Methods:Different crayfish shell proteolysates were prepared by hydrolysis of pepsin,alcalase protease,trypsin,flavor protease and papain,and their in vitro hypoglycemic and lipid-lowering activities were evaluated and peptide sequences were determined.The peptides sequence of Procambarus clarkii shells was identified by LC-MS/MS.Taking the crystal structure of the nuclear receptor PPARγ ligand binding region as the target,Autodock vina was used to simulate molecular docking to obtain crayfish shell peptides with potential hypoglycemic/lipid-lowering activities.Results:The PEP-PCSPHs had significant inhibitory effects on α-amylase andα-glucosidase activity,with IC50 values of(5.42±0.05)mg/mL and(7.11±1.01)mg/mL,respectively.The TRY-PCSPHs had the strongest inhibitory effect on pancreatic lipase activity,with an IC50 of(4.71±1.12)mg/mL,and exhibited the best in vitro binding effects on sodium glycinocholate.In addition,3 391 peptide sequences were identified in pepsin hydrolysates and 2 086 peptide sequences were identified in trypsin hydrolysates,and multiple hypoglycemic/lipid-lowering crayfish shell active peptides that could bind to PPARγ were screened through online website prediction and molecular docking.Conclusion:The shrimp shell peptides prepared by enzymatic hydrolysis of crayfish shells have potential hypoglycemic and lipid-lowering activities,which may play a role in improving glucose and lipid metabolism disorders.

Chinese perch (Siniperca chuatsi) is an important commercial fish species in China. Understanding the molecular mechanisms of growth and development of skeletal muscle is helpful for selection breeding and improving the growth rate of Chinese perch. We analyzed histological and transcriptomic differences in fast muscle of Chinese perch between 30 days post hatching (dph) and 60 dph using histological sections and high-throughput RNA-Seq. The results showed that the diameter of muscle fibers in 30 dph Chinese perch was mainly distributed in range of 30 - 40 μm, and that of 60 dph was primarily in the range of 40 - 50 μm. 34 differentially expressed genes (DEGs) were identified in the fast muscle of Chinese perch between 30 and 60 dph, of which 9 were up-regulated and 25 were down-regulated (60 dph vs 30 dph). The DEGs, including MYH4, ENO3, Bag3, krt13 and krt18, are associated with muscle cell differentiation and fusion in Chinese perch. The analysis of the protein-protein interaction network of DEGs revealed that FOS, junb and EGR1 may involve in the development of fast muscle. KEGG enrichment results showed that the up-regulated genes in the 60 dph were associated with several pathways related to metabolism and protein synthesis, such as glycosphingolipid biosynthesis and aminoacyl-tRNA biosynthesis. The results suggest that the development of fast muscle in Chinese perch from 30 to 60 dph is accompanied by an increase in muscle fiber diameter and changes in gene expression related to muscle cell differentiation and protein synthesis. Abbreviations: DEGs, differentially expressed genes; dph, days post hatching; FC, fold change; FDR, False Discovery Rate; GO, Gene Ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes; MyHCs, Myosin heavy chains; qRT-PCR, quantitative real-time PCR.

Lipids are necessary nutrients for fish and play an important role in growth and metabolism. This study analyzed the effects of dietary lipid levels on growth performance, flesh quality, antioxidant status, and lipid metabolism of juvenile rice flower carp (Cyprinus carpio). The results showed that the weight gain rate and specific growth rate increased initially and then decreased with increasing dietary lipid levels, which 5.82 % dietary lipid level had the best growth in rice flower carp. Dietary lipid levels also affect the nutrition and quality of fish flesh. With the increase of dietary lipid levels, the hardness, adhesiveness, springiness, gumminess and chewiness of muscle showed a trend of increase and then decrease. Moreover, there are similar changes in the activity of antioxidant enzymes in the muscle, and the content of ROS and MDA was significantly higher than other levels at 11.80 % dietary lipid level. The expression of Nrf2 mRNA and some downstream antioxidant enzyme genes was the contrary. Furthermore, the content of TG, TC, and LDL-C in serum and liver increased with increasing dietary lipid levels. Meanwhile, it was observed that the lipid accumulation increased in the liver. The mRNA expression of ATGL and CPT1 genes associated with lipid metabolism in liver increased firstly and then decreased, the expression of FASN, PPARγ, and SREBP1 gradually increased, and reached its maximum at 11.8 % dietary lipid level. The above results showed that the growth performance of juvenile rice flower carp was optimal when the dietary lipid level of 5.82 %, and the nutrition and quality of fish flesh also has good effects. However, the dietary lipid level of 11.80 % inhibited the weight gain and induced oxidative stress and lipid metabolism disorders of rice flower carp, which can affect their flesh quality and health.