Rearing temperature induces changes in muscle growth and gene expression in juvenile pacu (Piaractus mesopotamicus)

Association Between Muscle Growth and Transcription of a Mutant MSTN Gene in Olive Flounder (Paralichthys olivaceus)

Myostatin (MSTN, also known as growth differentiation factor-8 (GDF-8)), a member of the transforming growth factor β (TGF-β) superfamily, functions as a negative regulator of skeletal muscle development and growth. However, it is also expressed in a wide range of tissues in fish and thus may have more diverse roles in this group than in mammals. In this study, we assessed the genome-wide transcriptional expression pattern associated with the CRISPR/Cas9-mutated MSTN gene in the olive flounder (Paralichthys olivaceus) in association with changes in cell proliferation and transportation processes. There were no differences in the hepatosomatic index, and the growth of male and female fish increased in the F1 progeny of the MSTN mutants. Furthermore, the histopathological analysis showed that myostatin editing resulted in a 41.24% increase in back muscle growth and 46.92% increase in belly muscle growth in male flounder compared with normal flounder, and a 16.01% increase in back muscle growth and 14.26% increase in belly muscle growth in female flounder compared with normal flounder. This study demonstrates that editing of the myostatin gene enhances muscle growth in olive flounder, with a notably more pronounced effect observed in males. Consequently, myostatin-edited male flounder could represent a valuable asset for the flounder aquaculture industry.

Cloning, phylogenetic and expression analysis of two MyoDs in yellowtail kingfish (Seriola lalandi)

Yellowtail kingfish (Seriola lalandi) is a pelagic piscivore distributed circumglobally. Owing to its great market value, the growth mechanism of S. lalandi, including muscle development and growth, is a hot research topic. The myoblast determination protein (MyoD) gene has been shown to play an important role in formation of myoblasts and the function of somites in fish. The open reading frame (ORF) sequences of MyoD1 and MyoD2 in S. lalandi encoded 298 and 263 amino acids possessing three common characteristic domains, respectively, containing a myogenic basic domain, a bHLH domain, and a ser-rich region (helix III). S. lalandi MyoDs shared the highest identity with the MyoDs of S. dumerili. MyoDs are highly expressed in white muscle (P < 0.05) in S. lalandi. The expression level of MyoD1 mRNA was higher than that of MyoD2 mRNA during embryonic and early developmental stages, indicating that the two MyoD isoforms may have different roles in muscle formation. Moreover, the mRNA expression of MyoDs in the brain, pituitary, liver and muscle of endocrine growth axis were analyzed in the various sizes and ages stages. The expression levels of MyoDs in the different sizes and ages of S. lalandi showed that expression of both these genes was particularly high in 400-g fish and 2-year-old fish (P < 0.05). Moreover, the increases in the mRNA expression and plasma levels of growth hormone (GH) and insulin-like growth factor (IGF-I) were accompanied by an increase in mRNA expression of MyoDs, indicating the roles of GH and IGF-I in muscle development and growth of S. lalandi. Overall, the expression profiles of genes associated with muscle development are the first step taken towards deciphering fast growth mechanism in this important Seriola fish.

Selenium deficiency-induced high concentration of reactive oxygen species restricts hypertrophic growth of skeletal muscle in juvenile zebrafish by suppressing TORC1-mediated protein synthesis

Se deficiency causes impaired growth of fish skeletal muscle due to the retarded hypertrophy of muscle fibres. However, the inner mechanisms remain unclear. According to our previous researches, we infer this phenomenon is associated with Se deficiency-induced high concentration of reactive oxygen species (ROS), which could suppress the target of rapamycin complex 1 (TORC1) pathway-mediated protein synthesis by inhibiting protein kinase B (Akt), an upstream protein of TORC1. To test this hypothesis, juvenile zebrafish (45 d post-fertilisation) were fed a basal Se-adequate diet or a basal Se-deficient diet or them supplemented with an antioxidant (DL-α-tocopherol acetate, designed as VE) or a TOR activator (MHY1485) for 30 d. Zebrafish fed Se-deficient diets exhibited a clear Se-deficient status in skeletal muscle, which was not influenced by dietary VE and MHY1485. Se deficiency significantly elevated ROS concentrations, inhibited Akt activity and TORC1 pathway, suppressed protein synthesis in skeletal muscle, and impaired hypertrophy of skeletal muscle fibres. However, these negative effects of Se deficiency were partly (except that on ROS concentration) alleviated by dietary MHY1485 and completely alleviated by dietary VE. These data strongly support our speculation that Se deficiency-induced high concentration of ROS exerts a clear inhibiting effect on TORC1 pathway-mediated protein synthesis by regulating Akt activity, thereby restricting the hypertrophy of skeletal muscle fibres in fish. Our findings provide a mechanistic explanation for Se deficiency-caused retardation of fish skeletal muscle growth, contributing to a better understanding of the nutritional necessity and regulatory mechanisms of Se in fish muscle physiology.

Review: Understanding fish muscle biology in the indeterminate growth species pacu (Piaractus mesopotamicus)

The muscle phenotype of fish is regulated by numerous factors that, although widely explored, still need to be fully understood. In this context, several studies aimed to unravel how internal and external stimuli affect the muscle growth of these vertebrates. The pacu (Piaractus mesopotamicus) is a species of indeterminate muscular growth that quickly reaches high body weight. For this reason, it adds great importance to the productive sector, along with other round fish. In this context, we aimed to compile studies on fish biology and skeletal muscle growth, focusing on studies by our research group that used pacu as an experimental model along with other species. Based on these studies, new muscle phenotype regulators were identified and explored in vivo, in vitro, and in silico studies, which strongly contribute to advances in understanding muscle growth mechanisms with future applications in the productive sector.

Exposure to different temperature regimes at early life stages affects hatching, developmental morphology, larval growth, and muscle cellularity in rainbow trout, Oncorhynchus mykiss

In this study, the effects of temperature on hatching, yolk-sac absorption, larval metamorphosis, post-metamorphic growth, developmental morphology, and muscle cellularity were assessed in rainbow trout, during its early development (until 52 days post-hatching, dph). From the eyed-ova stage, embryos were exposed to either low (8 ± 1 °C, LT-8) or high (16 ± 1 °C, HT-16) temperatures until hatching. Following hatching, half of the sac-fry from LT-8 group were shifted to higher temperature (16 ± 1 °C, LHT-16), and half from HT-16 group were shifted to medium temperature (13 ± 1 °C, HMT-13), for larval rearing. Incubating the eyed-ova at 16 °C preceded the hatching by 6 days, synchronized hatching duration, and minimized hatchlings' size-variation. However, it yielded smaller and morphologically less developed individuals compared to those incubated continuously at 8 ± 1 °C. Post-hatch shifting of sac-fry to high and medium temperatures, respectively, from the initial low and high regimes differentially affected the length and weight of fish. The effect on length was immediate and temporary, but on weight, it appeared to be permanent. Red muscle hypertrophy was observed to be high in HT-16 and HMT-13 individuals (high-temperature incubated groups). White muscle hypertrophy was high in HT-16 and LHT-16 individuals (high post-hatch rearing temperature groups). The effect of early-life temperature regimes on developmental morphology was found to be strong at 22 dph (82.5%) and comparatively weak at 52 dph (65%). The post-hatch rearing temperature caused an immediate but temporary effect on fin development, mainly pectoral, caudal, and anal fin (seen only at 22 dph, not at 52 dph). Contrarily, incubation temperature affected fin position, in a delayed but persistent manner (subtle at 22 dph, but stronger at 52 dph). Overall, this study provides new insights on temperature-dependent changes in developmental morphology, muscle cellularity, and larval growth in rainbow trout and shows that incubation temperature affects ontogeny profoundly than post-hatch thermal regimes.

Dietary effects of aucubin on growth and flesh quality of grass carp (Ctenopharyngodon idellus) based on metabolomics

This aim of this study was to investigate the effects of dietary aucubin on the growth, flesh quality, and metabolomics of grass carp (Ctenopharyngodon idella). Five diets were designed with the aucubin inclusion of 0 (control diet), 0.2, 0.4, 0.6, and 0.8 g/kg (Auc-0.2, Auc-0.4, Auc-0.6, Auc-0.8) and were fed to grass carp with an initial body weight of 17.0 ± 0.2 g for 60 d. The results indicated that dietary aucubin did not significantly affect the growth performance of grass carp (P > 0.05). Compared to the control, dietary supplementation with 0.2 to 0.8 g/kg aucubin increased flesh hardness, chewiness, the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and the contents of total free amino acids (TFAA) and n-3 polyunsaturated fatty acids (n-3 PUFA) (P < 0.05). The contents of malondialdehyde (MDA) and lactic acid (LD) in the flesh were significantly decreased by the addition of 0.4 to 0.6 g/kg aucubin and by the addition of 0.6 to 0.8 g/kg aucubin (P < 0.05), respectively, while the content of delicious amino acids (DAA) was significantly enhanced by the addition of 0.4 to 0.8 g/kg aucubin (P < 0.05). Moreover, the contents of collagen and C22:6n3 (DHA) in the flesh of the Auc-0.8 group were significantly higher than those of the control (P < 0.05). In the metabolomics profiling of flesh, 133 and 135 named differential metabolites were identified in the Auc-0.4 and Auc-0.8 groups, respectively, compared to the control, and these metabolites were found to be involved in the second-grade pathways of "lipid metabolism" and "amino acid metabolism". Regarding gene expression, the mRNA levels of CuZn-SOD, CAT, COL1A1, COL1A2, Smad4, and FAS in flesh were upregulated in the Auc-0.4 and Auc-0.8 groups, and the expression levels of GPx, Nrf2, and TGF-β1 mRNA were also upregulated in the Auc-0.8 group (P < 0.05). In summary, dietary aucubin did not promote growth, but improved the flesh quality of grass carp, which might be associated with the TGF-β/Smad and Nrf2 pathways. The recommended supplementation level of aucubin in the diet of grass carp was 0.6 to 0.8 g/kg.

Degree of piRNA sharing and Piwi gene expression in the skeletal muscle of Piaractus mesopotamicus (pacu), Colossoma macropomum (tambaqui), and the hybrid tambacu

PiRNAs are a class of small noncoding RNAs that, in their mature form, bind to Piwi proteins to repress transposable element activity. Besides their role in gametogenesis and genome integrity, recent evidence indicates their action in non-germinative tissues. We performed a global analysis of piRNA and Piwi gene expression in the skeletal muscle of juveniles pacu (Piaractus mesopotamicus), tambaqui (Colossoma macropomum), and the hybrid tambacu to evaluate the degree of piRNA sharing among these three genotypes. Total RNA was sequenced and analyzed using specific parameters of piRNAs by bioinformatics tools. piRNA and Piwi gene expression was analyzed by RT-qPCR. We detected 24 piRNA clusters common to the three genotypes, with eight shared between pacu and tambacu, three between pacu and tambaqui, and five between tambaqui and tambacu; seven, five, and four clusters were unique to pacu, tambacu, and tambaqui, respectively. Genomic localization and fold change values showed two clusters and 100 piRNAs shared among the three genotypes. The gene expression of four piRNAs was evaluated to validate our bioinformatics results. piRNAs from cluster 17 were higher in tambacu than pacu and piRNAs from cluster 18 were more highly expressed in tambacu than tambaqui and pacu. In addition, the expression of Piwis 1 and 2 was higher in tambacu and tambaqui than pacu. Our results open an important window to investigate whether these small noncoding RNAs benefit the hybrid in terms of faster growth and offer a new perspective on the function of piRNAs and Piwis in fish skeletal muscle.

Selenium Status Affects Hypertrophic Growth of Skeletal Muscle in Growing Zebrafish by Mediating Protein Turnover

BACKGROUND

Selenium (Se) status is closely related to skeletal muscle physiological status. However, its influence on skeletal muscle growth has not been well studied.

OBJECTIVES

This study aimed to analyze the impacts of overall Se status (deficient, adequate, and high) on skeletal muscle growth using a growing zebrafish model.

METHODS

Zebrafish (1.5-mo-old) were fed graded levels of Se (deficient: 0.10 mg Se/kg; marginally deficient: 0.22 mg Se/kg; adequate: 0.34 mg Se/kg; high: 0.44, 0.57, and 0.69 mg Se/kg) as Se-enriched yeast for 30 d. Zebrafish growth, and Se accumulation, selenoenzyme activity, selenotranscriptome profiles, and oxidative status in the whole body, and selenotranscriptome profiles, histological characteristics, biochemicals, and gene and protein expression profiles related to muscle growth in the skeletal muscle were analyzed by model fitting and/or 1-factor ANOVA.

RESULTS

Se status biomarkers within the whole body and skeletal muscle indicated that 0.34 mg Se/kg was adequate for growing zebrafish. For biomarkers related to skeletal muscle growth, compared with 0.34 mg Se/kg, 0.10 mg Se/kg decreased the white muscle cross-sectional area (WMCSA) and the mean diameter of white muscle fibers (MDWMF) by 14.4%-15.1%, inhibited protein kinase B-target of rapamycin complex 1 signaling by 63.7%-68.5%, and stimulated the autophagy-lysosome pathway by 1.07 times and the ubiquitin-proteasome pathway (UPP) by 96.0% (P < 0.05), whereas 0.22 mg Se/kg only decreased the WMCSA by 7.8% (P < 0.05); furthermore, 0.44 mg Se/kg had no clear effects on skeletal muscle biomarkers, whereas 0.57-0.69 mg Se/kg decreased the WMCSA and MDWMF by 6.3%-25.9% and 5.1%-21.3%, respectively, and stimulated the UPP by 2.23 times (P < 0.05).

CONCLUSIONS

A level of 0.34 mg Se/kg is adequate for the growth of zebrafish skeletal muscle, whereas ≤0.10 and ≥0.57 mg Se/kg are too low or too high, respectively, for maintaining efficient protein accretion and normal hypertrophic growth.

Molecular Characterization of Hsp47 in Grass Carp (Ctenopharyngodon idella) and Its Correlation with Type I Collagen in Response to Fish Aerobic Exercise

Heat shock protein 47 (Hsp47) is a collagen-specific molecular chaperone that is indispensable for molecular maturation of collagen. In this study, hsp47 and hsp47-like cDNAs were cloned and characterized in grass carp (Ctenopharyngodon idella). The cDNAs were 1212 and 1218 base pairs long, respectively, and included an open reading frame encoding 403 and 405 amino acids. The molecular phylogeny based on the deduced amino acid sequences indicated that the correct sequences of the hsp47 and hsp47-like cDNA were obtained and the deduced proteins clustered distinctly into teleost clades. Primary structure analysis and characterization of Hsp47 and Hsp47-like shared the basic structure and biofunctions of Hsp47 in vertebrates. The spatial pattern of gene expression revealed that hsp47 and hsp47-like were relatively ubiquitous in different tissues and highly expressed in heart and skin. The expression levels of hsp47 and hsp47-like and type I collagen mRNAs varied similarly in different tissues. Type I collagen content increased significantly with the increase of water velocity in the muscle of grass carp in response to aerobic exercise. Among the gene expression changes of hsp47, hsp47-like, col1a1 and col1a2 in muscle that occurred in response to aerobic exercise, the change of type I collagen was most strongly correlated with hsp47 expression. Additionally, col1a1 showed the highest correlation with hsp47-like and col1a2 showed the highest correlation with hsp47. These findings suggest that grass carp Hsp47 and Hsp47-like are closely related to type I collagen synthesis. This study firstly suggests fish aerobic exercise can improve type I collagen content and Hsp47 gene expression in muscle of grass carp.

Slight Increases in Salinity Improve Muscle Quality of Grass Carp (Ctenopharyngodon idellus)

Fish muscle quality is an important parameter in the aquaculture industry. In this study, we analyzed and compared the muscle quality of grass carp (Ctenopharyngodon idellus) cultured at salinities of 0‰, 3‰, and 6‰ (GC0, GC3, GC6). There was no significant difference in crude protein and crude fat content of muscle between GC0 and GC3. Crude fat was significantly lower in GC6 compared to the other groups. GC3 and GC6 had higher hydroxyproline content, which suggested that these groups had higher collagen content. GC3 and GC6 had higher contents of free amino acids and umami amino acids than GC0, but there was no significant difference in sweet or sour amino-acid content among groups. GC3 and GC6 had better texture properties, including hardness, gumminess, chewiness, resilience, and springiness, than GC0. GC3 had the highest water-holding capacity among the groups. As the salinity increased, the diameter of muscle fibers decreased and the sarcolemma showed a thickening trend. These results suggest that a slight increase in salinity (i.e., 3‰) can effectively improve the muscle quality of grass carp.

Molecular characterization and gene expression analysis of the pro-inflammatory cytokines IL-1β and IL-8 in the South American fish Piaractus mesopotamicus challenged with Aeromonas dhakensis

In the present study, the complete characterization of cDNA and genomic sequences of IL-1β and IL-8, as well as the expression profile of these genes in the South American fish pacu (Piaractus mesopotamicus) is provided. The full-length pmIL-1β cDNA was composed of 1208 nucleotides that would produce a precursor peptide with 273 amino acid residues. A putative caspase-1 cleavage site, similar to what is found in mammalian IL-1β, was identified producing a mature peptide with a theoretical molecular weight of 17.21 kDa. The pmIL-8 cDNA sequence consisted of 1019 nucleotides which encoded a 95-amino acid protein with a theoretical molecular weight of 10.43 kDa that showed all typical CXC chemokine features, including a 20-residue signal peptide and four conserved cysteine residues. Constitutive mRNA expression was detected for both genes in the liver, head kidney, gill, intestine, skin and spleen. After a bacterial challenge, up-regulation was detected for both pmIL-1β and pmIL-8 in the spleen and head kidney at 12 h post-infection. At 24 h post-infection there was a decrease in the expression of both genes, with pmIL-8 showing a significant down-regulation in the liver and head kidney when compared to the control groups.

Modification of the content of n-3 highly unsaturated fatty acid, chemical composition, and lipid nutritional indices in the meat of grass carp (Ctenopharyngodon idella) fed alfalfa (Medicago sativa) pellets

A 120-d feeding trial was conducted to determine the effect of alfalfa (Medicago sativa) feeding on growth and chemical composition, fatty acid content, and nutritional and lipid indices of the meat of grass carp (Ctenopharyngodon idella). Two experimental diets were used: alfalfa pellet (AP) diet and artificial grain diet (GD). Final weight, feed conversion rate, and protein efficiency ratio were significantly greater in the GD group (P < 0.05). However, no differences in the length and condition factor were observed. The composition of the meat differed between treatments. The protein content was significantly greater in the AP group (P < 0.05), while the lipid and cholesterol contents were significantly greater in the GD group (P < 0.05). A greater proportion of saturated, n-6 polyunsaturated, and n-6 highly unsaturated fatty acids was obtained in the GD group. The AP group accumulated a greater concentration of eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids (P < 0.05). The fatty acid composition of the meat determined a significant decrease in the thrombogenicity index and saturation index (S/P) in the AP group (P < 0.05). The Elongase index was greater in the GD group (P < 0.05). In contrast, the AP group had a greater index of Δ9 Desaturase and Δ5 + Δ6 Desaturase for n-3 and n-6 fatty acids (P < 0.05). These results suggest that alfalfa feeding decreases the growth of C. idella but improves the quality of meat by increasing the protein, EPA, and DHA contents. It also reduces cholesterol content and improves nutritional indices.

Improvement of Muscle Quality of Grass Carp (Ctenopharyngodon idellus) With a Bio-Floating Bed in Culture Ponds

Muscle quality and the physiological condition of fish are affected greatly by the culture environment. In aquaculture ponds, a bio-floating bed planted with vegetation is often used to improve water quality. This study investigated the growth and muscle quality of grass carp (Ctenopharyngodon idellus) cultured in ponds equipped with bio-floating beds. Fish were cultured in two replicated pond groups from May to November. Fish in the first group were cultured in experimental ponds equipped with a bio-floating bed planted with Ipomoea aquatica, whereas fish in the other group were reared in control ponds without a bio-floating bed. Compared with control ponds, the experimental ponds had better water quality with significantly lower concentrations of nitrite and ammonia. Grass carp in the experimental group had greater muscle weight gain, a significantly higher content of crude protein, and a significantly lower crude fat level than fish in the control group. The levels of pH, water-holding capacity, and antioxidant capacity of muscle decreased significantly in the control group compared to the experimental group. Texture profile analysis revealed higher values of hardness, springiness, gumminess, and chewiness and lower values of cohesiveness and resilience of white muscle in the experimental group compared to the control group. The filets of fish in the experimental group also received higher grades in the sensory evaluation of springiness, overall acceptability, aroma, and palatability. These results indicate that growth performance and muscle quality of grass carp were improved by the presence of bio-floating beds in the culture ponds.

Diet Affects Muscle Quality and Growth Traits of Grass Carp (Ctenopharyngodon idellus): A Comparison Between Grass and Artificial Feed

Fish muscle, the main edible parts with high protein level and low fat level, is consumed worldwide. Diet contributes greatly to fish growth performance and muscle quality. In order to elucidate the correlation between diet and muscle quality, the same batch of juvenile grass carp (Ctenopharyngodon idellus) were divided into two groups and fed with either grass (Lolium perenne, Euphrasia pectinata and Sorghum sudanense) or artificial feed, respectively. However, the different two diets didn't result in significant differences in all the detected water quality parameters (e.g., Tm, pH, DO, NH3/[Formula: see text]-N, [Formula: see text]-N, [Formula: see text], TN, TP, and TOC) between the two experimental groups. After a 4-month culture period, various indexes and expression of myogenic regulatory factor (MRFs) and their related genes were tested. The weight gain of the fish fed with artificial feed (AFG) was nearly 40% higher than the fish fed with grass (GFG). Significantly higher alkaline phosphatase, total cholestrol, high density cholestrol and total protein were detected in GFG as compared to AFG. GFG also showed increased hardness, resilience and shear force in texture profile analysis, with significantly bigger and compact muscle fibers in histologic slices. The fat accumulation was most serious in the abdomen muscle of AFG. Additionally, the expression levels of MyoG, MyoD, IGF-1, and MSTNs were higher, whereas Myf-5, MRF4, and IGF-2 were lower in most positional muscles of GFG as compared to AFG. Overall, these results suggested that feeding grass could promote muscle growth and development by stimulating muscle fiber hypertrophy, as well as significantly enhance the expression of CoL1As. Feeding C. idellus with grass could also improve flesh quality by improving muscle characteristics, enhancing the production of collagen, meanthile, reducing fat accumulation and moisture in muscle, but at the cost of a slower growth.

Characterization and gene expression analysis of pacu (Piaractus mesopotamicus) inducible nitric oxide synthase (iNOS) following Aeromonas dhakensis infection

Nitric oxide (NO) is an important effector molecule which is involved in a myriad of biological processes, including immune responses against pathogens such as parasites, virus and bacteria. During the inflammatory processes in vertebrates, NO is produced by the inducible nitric oxide synthase (iNOS) enzyme in practically all nucleated cells to suppress or kill intracellular pathogens. The aim of the present study was to characterize the full coding region of the iNOS gene of pacu (Piaractus mesopotamicus), an economically and ecologically important South American fish species, and to analyze mRNA expression levels following intraperitoneal infection with the pathogenic bacterium Aeromonas dhakensis by means of quantitative real time PCR (qPCR). The results showed that the pacu iNOS transcript is 3237 bp in length, encoding a putative protein composed of 1078 amino acid residues. The amino acid sequence showed similarities ranging from 69.03% to 94.34% with other teleost fish and 57.70% with the human iNOS, with all characteristic domains and cofactor binding sites of the enzyme detected. Phylogenetic analysis showed that the iNOS from the red-bellied piranha, another South American characiform, was the closest related sequence to the pacu iNOS. iNOS transcripts were constitutively detected in the liver, spleen and head kidney, and there was a significant upregulation in the liver and spleen at 12, 24 and 48 h after infection with A. dhakensis. No significant variations were observed in the head kidney during the periods analyzed. These results show that iNOS expression was induced by A. dhakensis infection and suggest that this enzyme may be involved in the response to this bacterium in pacu.

Influence of temperature and exercise on growth performance, muscle, and adipose tissue in pacus (Piaractus mesopotamicus)

The aim of this study was to evaluate the effects of temperature and swimming exercise on fish growth in pacus (Piaractus mesopotamicus). Pacus weighing 0.9 - 1.9g and 2.7 - 4.2cm in standard length were cultivated at an initial density of 120 fish m^-3 in 3 recirculation systems containing 6 water tanks at a volume of 0.5m³ each at temperatures of 24, 28 and 32°C. At each temperature, three tanks were modified to generate exercise activity in the specimens and force the fish to swim under a current speed of 27.5cms^-1. At the end of the experiment, the following metrics were evaluated: fish performance, morphometry (length, width, height and perimeter in different body positions), and the diameter and density of muscle and subcutaneous ventral adipose tissues. At 28°C, pacus were both heavier and had greater weight gain after 240 days of cultivation. Additionally, exercise improved the feed conversion. An increase of 4°C (30°C) did not provide any improvement in the performance of the fish. However, swimming exercise improved the performance of pacus, providing increases of 38% and a 15% improvement in feed conversion. Both temperature and exercise influenced the body morphology (especially in the caudal region) and the cellularity of white and red muscle fibers and adipocytes.

Satellite cell activation and populations on single muscle-fiber cultures from adult zebrafish (Danio rerio)

Satellite cells (SCs), stem cells in skeletal muscle, are mitotically quiescent in adult mammals until activated for growth or regeneration. In mouse muscle, SCs are activated by nitric oxide (NO), hepatocyte growth factor (HGF) and the mechanically induced NO-HGF signaling cascade. Here, the SC population on fibers from the adult, ectothermic zebrafish and SC responsiveness to activating stimuli were assessed using the model system of isolated fibers cultured at 27 and 21°C. SCs were identified by immunostaining for the HGF receptor, c-met, and activation was determined using bromodeoxyuridine uptake in culture or in vivo. In dose-response studies, SC activation was increased by treatment with the NO-donor drug isosorbide dinitrate (1 mmol l(-1)) or HGF (10 ng ml(-1)) to maximum activation at lower concentrations of both than in previous studies of mouse fibers. HGF-induced activation was blocked by anti-c-met antibody, and reduced by culture at 21°C. The effect of cyclical stretch (3 h at 4 cycles per minute) increased activation and was blocked by nitric oxide synthase inhibition and reduced by culture at 21°C. The number of c-met+ SCs per fiber increased rapidly (by 3 h) after stretching. The character of signaling in SC activation on zebrafish fibers, in particular temperature-dependent responses to HGF and stretch, gives new insights into the influence of ectothermy on regulation of muscle growth in teleosts and suggests the use of the single-fiber model system to explore the basis of fiber hyperplasia and the conservation of regulatory pathways between species.