Long-chain polyunsaturated fatty acids (LC-PUFA) are essential nutrients for membrane function, development, and immunity in animals. Polychaetes are promising sources of LC-PUFA due to their endogenous biosynthetic capacity, but optimal feeding strategies to enhance their nutritional value remain poorly understood. We investigated the nutritional regulation of LC-PUFA biosynthesis in the marine polychaete Platynereis dumerilii fed three diets differing in fatty acid (FA) profiles: spinach, yeast, and commercial fish feed. Juveniles were cultured for 37 days at 35‰ salinity, and survival, growth, total lipids, FA profiles, and expression of elongases, desaturases, and putative transcription factors were analysed. Survival rates were high across all diets (93.3-95.0%), while growth was significantly reduced in spinach-fed worms, which showed a lower specific growth rate (1.5 ± 0.1% day-1) than worms fed yeast (2.2 ± 0.1% day-1) or fish feed (2.0 ± 0.1% day-1). Diet strongly affected FA composition: fish feed increased n-3 LC-PUFA, spinach elevated α-linolenic acid, and yeast enhanced n-6 LC-PUFA. Despite low dietary LC-PUFA, eicosapentaenoic acid levels remained stable, indicating active endogenous synthesis. Gene expression responses were diet-dependent, with elongase Elovl2/5 expression higher in fish-feed-fed worms (0.8 ± 0.3) than in yeast-fed worms (0.4 ± 0.1), while the front-end desaturase Fed1 (Δ5 activity) and methyl-end desaturase ω des1 (Δ12 activity) showed their highest expression in spinach-fed worms (3.9 ± 1.8 and 2.4 ± 1.0, respectively). Overall, P. dumerilii adjusted its lipid metabolism in response to dietary inputs, demonstrating transcriptional plasticity and reinforcing its potential as a sustainable source of LC-PUFA.
Environmental changes affect microplastic (MP) biofilms, but how the resulting bacterial adsorption influences infection rates and physiological responses in fish remains unclear. This study investigated the combined effects of temperature (18 °C, 22 °C, and 26 °C) and MP size (102 and 220 μm) on biofilm formation and the subsequent effects on Vibrio harveyi infection and physiological responses in Korean rockfish Sebastes schlegelii. Biofilms were formed on MPs over 21 days under different temperature conditions, followed by a 5-day co-exposure experiment with V. harveyi. Biofilm formation markedly increased with rising temperature and was more pronounced on smaller MPs owing to their larger specific surface area, with the highest levels observed in the 26 °C small MP group. Correspondingly, the abundance of V. harveyi on MPs and its accumulation in fish tissues were markedly elevated, indicating enhanced bacterial transport and internalization. Co-exposure to MPs and V. harveyi induced oxidative stress, as evidenced by increased reactive oxygen species production in the liver, along with upregulation of antioxidant enzymes. Immune responses were also activated, with marked increases in the mRNA expression levels of interleukin-1 beta (il-1β), tumor necrosis factor alpha (tnf-α), and c-c chemokine ligand 25 (ccl25), particularly under high-temperature and small MP conditions. In situ hybridization further confirmed increased il-1β expression in liver tissues. Overall, elevated temperature and smaller MPs promoted biofilm formation, facilitating bacterial infection and inducing oxidative stress and immune responses. These findings suggest that climate-driven warming and MP pollution may synergistically increase disease risks in marine fish, with important implications for aquaculture and marine ecosystem health.
In decapod crustaceans, red pigment-concentrating hormone (RPCH) is considered an ortholog of insect adipokinetic hormone (AKH); both belong to the conserved arthropod AKH/RPCH neuropeptide family. Research on crustacean RPCH has focused primarily on pigmentary functions, but the tissue-level roles of RPCH beyond its role in pigmentation are poorly understood. In this study, we used RNA interference to knock down the rpch gene in Litopenaeus vannamei (Lv-rpch) and integrated transcriptomic analysis, reverse transcription quantitative polymerase chain reaction (RT-qPCR) validation, biochemical assays, and histological examination to characterize responses in the gill and hepatopancreas. The two tissues exhibited distinct differentially expressed gene (DEG) profiles, comprising 190 DEGs in the hepatopancreas and 768 in the gill. Gill DEGs were enriched mainly in defense-related processes, lysosome-associated categories, structural components, and carbohydrate metabolism pathways. In the hepatopancreas, enrichment primarily involved transport, protein processing, oxidoreductase activity, xenobiotic metabolism, and carbohydrate and lipid metabolism. Biochemical assays revealed lower superoxide dismutase (SOD) activity and malondialdehyde (MDA) content in both tissues, higher gill lysozyme (LYS) activity, and lower hepatopancreatic lipase activity. Trypsin activity did not change. Histological examination indicated morphological alterations in both tissues after Lv-rpch knockdown. Taken as a whole, these results link Lv-rpch knockdown to tissue-specific transcriptomic, biochemical, and histological responses in L. vannamei, although the underlying causal mechanisms remain to be established.
The permanently sub-zero temperatures and high oxygen solubility of the Southern Ocean promote the formation of reactive oxygen species (ROS) in the tissues of resident organisms, imposing persistent oxidative stress. Antarctic notothenioid fish have evolved efficient antioxidant systems to counter this pressure. This study reports the first molecular characterisation of the catalase (cat) transcript and deduced protein (CAT) sequence, together with tissue-specific CAT activity, in two Antarctic species with contrasting physiological traits: the red-blooded notothenioid Trematomus bernacchii and the haemoglobin-less icefish Chionodraco hamatus. Integrating cDNA sequencing with transcriptomic data, we reconstructed full-length cat coding sequences, performed Bayesian and maximum-likelihood phylogenetic analyses, and compared electrostatic surface properties using structural modelling. The cat transcript levels and CAT activity were quantified in liver, gills, heart, and skeletal muscle. Catalytic, NADPH-binding, and substrate-channel residues were fully conserved across Antarctic and non-Antarctic teleosts, consistent with strong purifying selection. T. bernacchii displayed a markedly more negative electrostatic surface than the icefish and non-Antarctic species, a pattern consistent with the increased surface acidity typical of cold-adapted proteins and with the higher oxidative burden of the red-blooded condition. The icefish showed a near-neutral electrostatic profile, consistent with its haemoglobin-less physiology. The liver was the principal site of both cat transcript accumulation and CAT activity in both species. Non-hepatic tissues showed a translation index below unity, consistent with post-transcriptional and/or post-translational regulation, with maximum translational efficiency shifting from the liver in T. bernacchii to the heart in C. hamatus. These findings suggest that enzyme surface properties and tissue-specific translational regulation may jointly contribute to antioxidant homeostasis under extreme marine conditions.
Fish skin mucus covers the body surface, serving as a physical and chemical first line of defense at the interface with the aquatic environment. Epidermal mucus provides a protective cushioning layer and contains numerous bioactive molecules involved in immune defense, antimicrobial activity, and tissue repair. During body-surface injury, direct contact between the plasma components and the mucus layer may influence plasma clotting. However, the role of epidermal mucus in this process remains poorly understood. This study investigated, under in vitro conditions, the effects of epidermal mucus from Japanese flounder (Paralichthys olivaceus) on plasma coagulation and examined coagulation-modulating components through biochemical fractionation. The addition of crude mucus to the flounder plasma shortened the fibrin clotting time and accelerated thrombin substrate cleavage under both prothrombin time-like and activated partial thromboplastin time-like conditions. Affinity fractionation of crude mucus using benzamidine-Sepharose showed that both the bound and unbound fractions retained procoagulant activity, suggesting that the observed activity was not solely attributable to serine protease-like components. Furthermore, size-based fractionation of the crude mucus using an ultrafiltration membranes and size-exclusion chromatography showed that procoagulant activity was distributed across multiple fractions in the approximate 29 to >2000 kDa range, whereas lower-molecular-weight fractions showed anticoagulant activity. These findings suggest that modulation of coagulation by mucus may contribute to the balance between local clot formation and the prevention of excessive coagulation at the epithelial surface.
There is an increasing interest in the capture and welfare of wild caught fish. Despite this, the methods used to catch and kill fish in commercial fisheries remain associated with significant welfare concerns. It is therefore necessary to determine neurophysiological, and endocrine responses of fish to different fishing gear in order to understand and highlight the welfare challenges affecting wild fish populations. We characterized neuronal activity, neuroendocrine, neurochemical and molecular responses of wild cod caught with Danish seine, fish traps, longline or gillnet. Fish caught by Danish seine had a significant region-specific increase in neuronal activity in the tubercular nuclei (TN) of the hypothalamus, accompanied by a reduced stress response profile in monoamine neurochemistry and plasma cortisol, in comparison to fish caught with the other fishing methods. In contrast, the fish caught with gillnet displayed the highest stress response reactivity. Total transcriptome analysis of the TN revealed that fish caught by gillnet, longline and fish traps had a neural gene expression pattern associated with energy metabolism, neuroinflammation and neurodegeneration. This suggests that the stress imposed by these fishing methods activates pathways that, over time, may lead to neural dysfunction. These results emphasize that Danish seine-caught fish had relatively better welfare compared to fish caught using the other fishing methods, whereas the gillnet-caught fish had relatively poorer welfare outcomes. Furthermore, we present several candidate genes that may be suitable as markers for stress-related neurodegenerative conditions that should be further studied to elucidate their specific functions within the fish brain.
Starvation is a common stressor in aquaculture that can markedly affect intestinal health and function in fish. This study focused on yellow cheek carp (Elopichthys bambusa, initial body weight: 221.36 ± 6.75 g; initial body length: 28.47 ± 0.56 cm) to explore how short-term (8 days) and long-term (28 days) starvation influence intestinal morphology, expression of key functional genes, and gut microbiota composition. Additionally, Spearman's rank correlation analyses were conducted to explore potential host-microbe interactions. The results showed that short-term starvation did not significantly affect intestinal muscle layer thickness or villus height, but markedly upregulated genes associated with autophagy and apoptosis such as bcl-2-associated X protein 2 (bax2), bcl-2-like protein 1 (bcl2l1), and cysteine-aspartic acid protease 8(casp8). It also increased microbial diversity and altered the composition of dominant gut microbiota. In contrast, long-term starvation significantly suppressed the expression of copper/zinc superoxide dismutase (Cu-Zn sod), casp3a, and casp9, increased the number of goblet cells, inhibited muscle layer development, and weakened the correlation between gut microbes and host gene expression. In summary, short-term starvation appears to maintain intestinal homeostasis through activation of autophagy- and apoptosis-related pathways in conjunction with microbial restructuring. However, prolonged starvation inhibited muscularis development, increased goblet cell density, downregulated antioxidant and immune-related gene expression, and weakened the associations between the host and its microbiota. These findings provide new insights into starvation-induced physiological responses and contribute to gut health management strategies in aquaculture.
Understanding the thermal adaptation of protein function is key to predicting species distributions under climate warming. This study investigated the secondary structure of cytosolic malate dehydrogenase (cMDH) from three intertidal snails with distinct heat tolerance. Despite minimal sequence differences (2-3 amino acids) in cMDHs, their heat tolerance differed significantly. Circular dichroism spectra of wild-type and experimentally-generated mutant cMDHs confirmed that all are α-helix-rich proteins. The cMDH from the extremely heat-tolerant Echinolittorina malaccana had a significantly higher α-helix content than that from heat-tolerant E. radiata. A substitution from glycine to serine at residue 48 significantly reduced the α-helix content of cMDH (p < 0.05), however, substitutions at residues 4 and 114 did not significantly alter α-helix content (p > 0.05). Furthermore, the extremely heat-tolerant cMDH exhibited fewer salt bridges and hydrogen bonds, suggesting greater structural flexibility that may facilitate functional dynamics under heat stress. The findings demonstrate that the secondary structure content, particularly α-helix percentage, may be associated with the temperature adaptation of cMDHs.
Anemonia viridis is a species of sea anemone (Cnidaria:Anthozoa) currently experiencing negative environmental impacts on their natural populations in the Mediterranean Sea. This species has excellent regeneration capacity, such that asexual reproduction can be induced in captivity via longitudinal bisection, but there is no information about the impact of this procedure on the animal’s physiology beyond short-term responses. The goal of this work was to assess the stress response of A. viridis during and after regeneration. We measured oxidative and immunological state markers in control and bisected anemones, at 4 weeks post-injury and 20 weeks post-injury. We then performed Principal Component Analysis (PCA) to identify trends at the multivariate level. Additionally, we carried out a histological evaluation of the wound healing process during the first 7 days post-injury. Higher antioxidant enzymatic activity was found in bisected anemones, mainly in catalase and glutathione-dependent enzymes. This response was often reverted by 20 weeks post-injury in tentacles. No differences in lipid peroxidation were observed. Phosphatase activities were unaltered within the studied time-frame. Histological analysis indicated recruitment of amoebocytes, the immune effector cells in anthozoans, and appearance of fibrillar mesoglea, detectable between 6 h and 24 h post-bisection. Results suggest the antioxidant response was effective containing oxidative damage. Longitudinal fission appears to be a viable technique for inducing asexual reproduction in A. viridis without triggering a stress response, and could reduce dependence of the market on the natural environment.
The Sma- and Mad-related protein 3 (SMAD3) is a pivotal downstream mediator of the transforming growth factor-β (TGF-β) signaling pathway, playing a central role in collagen synthesis and fibrotic processes in mammals. However, its function is tissue context-specific and remains poorly elucidated in teleosts. In this study, we identified and functionally characterized smad3 from Nibea coibor (designated as Ncsmad3), an important marine economic fish valued for its collagen-rich swim bladder. The Ncsmad3 gene encodes a 425-amino acid protein with conserved Mad Homology 1 (MH1) and Mad Homology 2 (MH2) domains, showing the highest identity with other fish Smad3 orthologs. Tissue expression profiling revealed ubiquitous Ncsmad3 expression. The factors promoting collagen synthesis (Tgf-β1, leucine, proline, hydroxyproline) significantly upregulated the expression of Ncsmad3 in swim bladder cells. Furthermore, bioinformatics analysis revealed multiple Smad-binding elements in the collagen alpha 1 chain (col1a1) and collagen I alpha 2 chain (col1a2) promoters, and dual-luciferase assays confirmed that Ncsmad3 enhances their promoter activity. These results underscore the role of Ncsmad3 in regulating collagen synthesis in teleosts, providing a potential molecular target for improving collagen deposition in aquaculture species.
Circulating biomarkers are commonly measured by researchers to assess the health of wild animals. Previous studies of mammals have reported variations in plasma glucose concentrations between peripheral and cardiac blood samples, as well as between venous and arterial samples. To our knowledge, however, no studies have compared plasma metabolites collected from different sampling sites in wild-caught birds. Adult mourning doves of both sexes (n = 13) were captured using walk-in style funnel traps as part of a separate study. Blood samples were collected from the ulnar vein of unanesthetized birds. Following euthanasia with sodium pentobarbital (200 mg/kg, i.p.), blood samples were also collected from the cardiac left ventricle (LV). Plasma was separated from formed elements and analyzed for glucose and uric acid concentrations using commercially available kits. In contrast to mammals, there were no significant differences in glucose concentrations between sampling sites (paired t-test; p = 0.6582), and glucose concentrations from ulnar vein and cardiac LV samples were positively correlated (Spearman r = 0.7363; p = 0.0041). In contrast, ulnar vein samples had higher uric acid concentrations (paired t-test; p = 0.0007), and no correlation was observed between ulnar vein and cardiac LV samples for this metabolite (Spearman r = 0.3956; p = 0.1809). Additionally, glucose and uric acid concentrations were not significantly correlated within either the ulnar vein (Spearman r = -0.2363; p = 0.4371) or cardiac LV (Spearman r = 0.3462; p = 0.2466) samples. These findings highlight the importance of considering sampling site and condition when measuring plasma metabolites and when comparing results across studies.
This study evaluated the potential for tauroursodeoxycholic acid (TUDCA) to ameliorate the negative effects associated with high soybean meal (SBM) diets in the grass carp (Ctenopharyngodon idellus). Grass carp (initial weight 25.42 ± 0.16 g) were fed one of four diets for 8 weeks: a control diet (fish meal [FM]-based), Control+TUDCA (0.5 g/kg), a high SBM diet (100SBM, completely replacing FM), or 100SBM + TUDCA. The 100SBM diet reduced growth performance and feed efficiency. However, TUDCA supplementation did not reverse these growth deficits. The 100SBM diet induced hepatopancreatic lipid accumulation, which was attenuated by TUDCA. Regarding hepatic lipid metabolism, the SBM diet significantly increased apolipoprotein E gene expression, while TUDCA supplementation decreased acetyl-CoA carboxylase gene expression. Hepatic farnesoid X receptor (FXR) signaling and endoplasmic reticulum stress (ERS)-related gene expression remained unaltered across all dietary treatments. Histological analysis revealed that the 100SBM diet reduced intestinal villus height and muscle thickness while increasing capillary width. TUDCA ameliorated SBM-induced muscular atrophy and capillary dilation in the foregut and midgut. Furthermore, the 100SBM diet elevated inflammatory cytokine concentrations (interleukin-6, tumor necrosis factor-α, and interleukin-1β) in the foregut and midgut, an effect mitigated by TUDCA. Intestinal FXR and ERS pathways displayed segment-specific modulation by TUDCA, with significant activation in the midgut and hindgut, respectively. Overall, although it lacked significant growth-promoting effects, TUDCA protected against SBM-induced hepatopancreatic lipid accumulation and intestinal inflammation, partially through the modulation of intestinal ERS and FXR signaling pathways.
Hepatocyte nuclear factor 4 alpha (HNF4α) plays a critical role in hepatic lipid metabolism in mammals, particularly with respect to fatty acid β-oxidation (FAO). However, its gene structure and biological function in fish remain largely unknown. In this study, the hnf4α gene, which encodes a peptide consisting of 454 amino acids, was characterized from the tiger puffer (Takifugu rubripes). As a member of the nuclear receptor superfamily, the Hnf4α protein contains a conserved deoxyribonucleic acid-binding domain at the N-terminus and a C-terminal multifunctional hydrophobic ligand-binding domain, which binds fatty acids. Amino acid sequence alignment, gene structure comparison, and phylogenetic analysis indicated that tiger puffer Hnf4α is highly conserved relative to mammals and other teleosts, suggesting evolutionarily conserved functions. Tissue distribution analysis indicated that hnf4α transcript levels were highest in the intestine, followed by the liver and kidney. To explore whether HNF4α participates in regulating hepatic FAO in tiger puffer, a lipid accumulation model was first established in hepatocytes using 200 μM oleic acid (OA). Subsequent treatment with 100 μM docosahexaenoic acid (DHA) visually diminished OA-induced lipid droplets accumulation, accompanied by a significant reduction in triglyceride content and upregulation of hnf4α as well as several FAO-related genes, including peroxisome proliferator-activated receptor alpha (pparα), peroxisome proliferator-activated receptor γ coactivator 1 alpha (pgc1α), and carnitine palmitoyltransferase 1ab (cpt1ab). Taken together, these findings offer initial evidence that Hnf4α may be involved in the DHA-induced promotion of FAO in tiger puffer hepatocytes.
Hepatic lipid homeostasis is crucial for overall liver health, necessitating an understanding of its underlying physiological mechanisms. While G protein-coupled receptor 119 (GPR119) has emerged as a key receptor in lipid metabolism, its physiological role in the liver remains poorly explored. We investigated the role of Gpr119 in hepatic lipid homeostasis using the zebrafish hepatocyte cell line (ZFL), alongside both high-fat diet (HFD)-induced and genetic knockout (gpr119-/-) zebrafish models. We demonstrated that pharmacological activation of Gpr119 by the agonist MBX-2982 attenuated HFD-induced hepatic steatosis and liver injury. Conversely, endogenous gpr119 deficiency induced spontaneous hepatic lipid accumulation and elevated serum transaminase activities under basal physiological conditions. Mechanistically, Gpr119 signaling limits lipid accumulation by coordinately downregulating de novo lipogenesis while promoting lipolysis and very-low-density lipoprotein (VLDL)-dependent lipid clearance. Collectively, our findings indicate that Gpr119 is a regulator of hepatic lipid homeostasis, functioning to restrict lipid supply and accelerate lipid clearance. This study provides in vivo genetic evidence highlighting the role of Gpr119 in hepatic lipid homeostasis, thereby advancing our physiological understanding of liver function and lipid handling.
Dopamine (DA) regulates diverse physiological processes via dopamine receptors (DRs), yet the molecular activity and physiological relevance of dopamine receptor D4 paralogs in teleosts remain unclear. Here, we identified and characterized Drd4b (LcDrd4b) from Larimichthys crocea. Sequence and phylogenetic analyses supported its assignment to the DRD4 lineage. Heterologous expression in human embryonic kidney (HEK293) cells showed that LcDrd4b exhibited membrane-associated localization and DA-associated redistribution, reduced forskolin-stimulated cyclic adenosine monophosphate (cAMP) accumulation, and activated extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Gene expression profiling revealed relatively high Lcdrd4b expression in the intestine at early reproductive stages and prominent gonadal expression at stage IV, especially in mature testes. Tyrosine hydroxylase (Lcth) showed high hepatic expression at stages II-III and a sex-related shift at stage IV. Together, these findings establish LcDrd4b as a functional DR in a marine teleost and provide a molecular basis for further studies of DA signaling in teleost physiology.
Elongation of very long-chain fatty acids (Elovl) proteins play essential roles in the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFAs). However, endogenous LC-PUFA biosynthesis in crustaceans remains incompletely understood, partly due to limited functional characterization of elongases. In this study, we cloned and functionally characterized an elovl1/7-like gene from the red swamp crayfish (Procambarus clarkii). The full-length cDNA contains an open reading frame of 1155 bp encoding a 384-amino acid protein with five predicted transmembrane domains and a conserved histidine box (HXXHH). Phylogenetic analysis showed that P. clarkii Elovl1/7-like clusters with crustacean homologs, forming a distinct clade separate from vertebrate Elovl1 and Elovl7. Tissue expression analysis revealed ubiquitous expression, with the highest levels in the hepatopancreas and gill. Functional characterization using a heterologous yeast expression system demonstrated that P. clarkii Elovl1/7-like catalyzed the elongation of C18:1n-9 to C20:1n-9 and converted C18:2n-6 and C18:3n-3 to their corresponding C20 products, while no elongation activity was detected toward C20 or C22 polyunsaturated fatty acid substrates. These results indicate that the enzyme preferentially acts on C18 fatty acids and has a limited role in elongating longer-chain substrates. This study provides functional evidence for the involvement of Elovl1/7-like in fatty acid elongation in P. clarkii and contributes to understanding lipid metabolism in crustaceans.
The remarkable diversity of decapod crustaceans inhabiting a wide range of osmotic environments reflects their evolutionary success, likely driven by the variety of mechanisms for body fluid regulation involving both molecular and systemic adaptations. In recent decades, considerable research has focused on the osmoregulatory strategies of decapod crustaceans occupying distinct osmotic niches. However, limited information is available on the effects of salinity on the activity and expression of gill (Na+, K+)-ATPase in terrestrial and semi-terrestrial species. This study investigates key aspects of osmoregulation in the semiterrestrial crab Goniopsis cruentata during acclimation to varying salinity levels. After exposure to 10, 20, 30, and 40 ‰S for 5 days, the crabs exhibited strong hyper- and hypo-osmoregulatory capabilities, reaching isosmotic conditions at approximately 30 ‰S. The Total Regulatory Capacity, expressed as a dimensionless ratio of hemolymph to external osmolality variation, was 0.08, with hyper- and hypo-osmoregulatory values of 0.06 and 0.12, respectively. Goniopsis cruentata demonstrated increased mRNA expression of (Na+, K+)-ATPase under hypo-osmotic conditions, despite a concurrent reduction in enzyme activity. These findings suggest that both hyper- and hypo-osmoregulatory mechanisms in G. cruentata are dependent only minimally on branchial (Na+, K+)-ATPase activity and instead rely more strongly on other ion transporters to maintain body fluid homeostasis. These results contrast with observations in aquatic crabs, in which branchial (Na+, K+)-ATPase plays a central role in osmoregulation.
In the present study, myoblast determination protein (myod) and myogenic factor 5 (myf5), two critical primary myogenic regulatory factors (MRFs) that govern muscle growth were characterized in snow trout (Schizothorax richardsonii). In addition, their mRNA expression was examined in relation to age, sex, nutritional conditions and temperature regimes. The full-length of Srmyod and Srmyf5 mRNA sequences were 1638 and 1397 nucleotides, respectively; with open reading frames of 825 and 723 nucleotides, which encoded proteins of 273 and 240 amino acid residues. In silico protein-protein interaction, nuclear localization signals, ligand-binding residues and tertiary protein structures indicated their putative roles in dimerization, DNA binding, and transcriptional activation. With respect to muscle mRNA expression, Srmyod was upregulated in older fish (2+ age) and conversely Srmyf5 was higher in younger fish (0+ age). There were no sex-dependent differences in MRFs expression. Three weeks of refeeding following three weeks of starvation significantly upregulated the transcriptional levels of both MRFs, corroborating the compensatory growth potential of the fish. The expression of Srmyf5 and Srmyod were concurrently high in fish fed 35% dietary protein. In contrast, dietary lipid levels (3-13%) had no significant effect on MRF expression. With respect to rearing temperature (6-24 °C), Srmyf5 expression showed marked upregulation at 18 °C, consistent with optimal fish growth. Overall, these findings reveal the conserved molecular profile and distinct transcriptional regulation of myod and myf5 in snow trout, under different biological, nutritional and environmental determinants of growth.
