White Muscle Fibres Research Articles

Distribution of Metals in Red and White Axial Muscles of Three Fish Species from the Krasnoyarsk Reservoir

The content of metals in fish fillet is an important criterion for food safety and nutritional benefits. Fish fillet is composed of both white and red muscles, but the standard method only detects metal content in white muscle. The true metal content in fish fillet can be underestimated due to this approach. So far, metal content in different types of muscle tissue of freshwater fish remains virtually unstudied. The aim of the present research was to study the metal content in red and white muscles of roach Rutilus rutilus, bream Abramis brama and pike Esox lucius that live in the Krasnoyarsk reservoir. Twenty metals were measured in the dry mass of red and white muscles of three fish species using inductively coupled plasma (ICP-OES) spectrometry. The contents of macronutrients such as K, Ca and Mg were higher in white muscle fibers and Na – in red fibers. Of the 16 metals regarded as trace elements, the highest contents in the muscles were noted for Fe (20.5-177.8 μg/g), Zn (26.7-79.0 μg/g), and Al (15.2- 67.2 μg/g), regardless of the fish species and type of tissue. Li (0.01-0.09 μg/g) and Cd (0.01-0.03 μg/g) had the lowest concentrations. Among trace elements, the contents of Cu and Fe were significantly higher in the dry biomass of red muscle compared with white muscle for the three fish species. The content of Zn was higher in the red muscle of bream and pike. Almost all other trace elements also tended to accumulate in higher concentrations in the red muscle. Differences between red and white muscles in the contents of trace elements such as Pb and Sr were species-specific. The distribution of metals between the two types of muscle fibers demonstrated by the freshwater species examined in this study was similar to the distribution of metals in marine fish, except the distribution of Sr. Thus, the greater capacity of the red muscle for accumulating most heavy metals confirmed in the present study may indicate a greater risk to health in eating this type of tissue

Histostructure of the Locomotor Apparatus in the Three Deep-Water Species of Lanternfishes (Myctophidae): Myctophum punctatum, Notoscopelus kroyeri, and Lampanyctus macdonaldi

The morphological and functional characteristics of the somatic musculature’s histological structure have been studied for three species of deep-sea fish from the Myctophidae family: spotted lanternfish Myctophum punctatum, lancet fish Notoscopelus kroyeri, and rakery beaconlamp Lampanyctus macdonaldi. The average diameter of fast-twitch and slow-twitch muscle fibers in all studied species is large, and this indicator is highest in rakery beaconlamp. All species are characterized by a craniocaudal gradient of a decrease in the size of white muscle fibers. The shape of the fibers, from angular polygonal (spotted lanternfish) to the oval (rakery beaconlamp) and round (lancet fish), is a distinctive feature from other species of bony fish. In spotted lanternfish, a group of fibers of very small diameter, which are presumably small, slow-twitch oxidizing fibers, was also noted between the white and red muscles. The red muscles in the studied fish are poorly identified, since they are poorly developed. The studied species have a well-developed connective tissue carcass of white muscles, which indicates a certain friability of fast-twitch muscles. Both the red and white muscles in lanternfishes are a place of intense deposition of lipid reserves. Apparently, the high lipid content in muscle tissue helps to reduce the specific gravity of fish and increase their buoyancy.

From muscle to food: oxidative challenges and developmental anomalies in poultry breast muscle

The glycolytic capacity in the "white muscle fibers" found predominantly in broiler and turkey breast muscle have long been recognized as being key components contributing to optimal pH changes post-harvest and the quality of breast muscle products. The pectoralis major (PMAJ) is the predominant breast muscle and is almost exclusively comprised of fast-twitch glycolytic (anaerobic) type IIb muscle fibers (white). In nature, the pectoralis muscles are designed to meet the intense, periodic energy demands of flight in contrast to the continual, oxidative metabolism (aerobic) inherent to the type I slow twitch fibers (red) in the thigh and drum. Within the past decade, it has been recognized that increased breast muscle yield in modern broiler strains may have contributed to muscle myopathies characterized by visible white striations (white striping; WS) often accompanied by surface hemorrhages and areas of extreme firmness (woody breast; WB). The research to date has primarily addressed differences in muscle physiology and processing characteristics in "normal" and "abnormal" muscle samples from older broilers. One hypothesis is that the extensive accretion of protein in a poorly vascularized breast muscle overwhelms the capacity for coping with excessive production of reactive oxygen species and the term "oxidative stress" has been used to describe this condition. There are few recent reports in poultry, however, which have addressed the potential negative physiological effects imposed by multiple layers of fascia surrounding individual muscle fibers, fiber bundles, and intact muscles on circulation and oxidative stability. The objective of this review is to support our hypothesis that the extensive accretion of breast muscle in a poorly vascularized and tightly bound PMAJ could be creating a "compartment syndrome" like condition leading to the development of the WS and WB anomalies in heavy, high yielding birds. Recent gene expression data support this hypothesis.

Relationship between the characteristics of rigor-mortis-related actomyosin and muscle fiber types in the ordinary muscle of various fishes.

Rigor mortis occurs when muscle extension vanishes through the irresistible coupling of actin and myosin by the consumption of adenosine triphosphate as energy. To clarify the cause of the differences in the progression of rigor mortis, seven fish species were used as samples. The superprecipitation reaction and Mg2+ -ATPase activity of actomyosin in dorsal ordinary muscle were measured, and the slope of the regression line between these two variables was calculated for each fish specimen. The fiber types of the dorsal ordinary muscle in each sample fish were discriminated by the stability of actomyosin ATPase at acid and alkaline preincubations. Positive correlations were found between Mg2+ -ATPase activity and the superprecipitation reaction of actomyosin in all 27 fish specimens. The slopes of the regression lines were different not only between fish species but also in fish specimens within the same species. The area ratios of pink muscle fibers and the IIa and/or IIb subtypes of white muscle fibers in the dorsal ordinary muscle were also different between fish species, as well as in specimens within the same fish species. A positive correlation was found between the area ratios of pink muscle fibers in dorsal ordinary muscle and the slopes of the regression line. It was suggested that the differences in characteristics of rigor-mortis-related actomyosin of fish might have been caused by the differences in the interposition ratio of muscle fiber types, especially of the pink muscle fiber type, in the dorsal ordinary muscle. © 2019 Society of Chemical Industry.

Low salinity negatively affects early larval development of Nile tilapia, Oreochromis niloticus: insights from skeletal muscle and molecular biomarkers.

The present study evaluated the effects of low salinity on the early larval development of Oreochromis niloticus, specifically histological damage to white muscle, morphology of the yolk-sac surface and trunk area, and molecular expression of apoptosis and cell proliferation biomarkers. Newly hatched larvae were submitted to four salinity treatments for a period of 48 or 72 h, in duplicate: (S0) freshwater, (S2) 2 g l-1, (S4) 4 g l-1, and (S6) 6 g l-1NaCl. Larval development was examined using histology, electron microscopy, enzyme-linked immunosorbent assay (ELISA), and morphometry. At the yolk-sac surface, larvae of S4 and S6 displayed alterations to the apical opening of chloride cells that may be related to osmotic expenditure caused by the increased salinity. Caspase-3 expression did not differ significantly among treatments, however significantly lower proliferating cell nuclear antigen (PCNA) expression (P < 0.05) suggested minor cell proliferation in larvae of S4 and S6 compared with S0 and S2. Furthermore, there was a significant reduction in both trunk area and percentage of normal white muscle fibres (WF) in larvae of S4 and S6. Vacuolated areas and myofibrils concentrated at the cell periphery and found in the white muscle from larvae exposed to saline environments suggested disturbance to muscle development. Oedema and mononuclear infiltrate were also observed in the white muscle of S4 and S6 larvae. Together these results indicated that treatments with 4 and 6 g l-1 NaCl may cause osmoregulation expenditure, morphological alterations to the yolk-sac surface and histological damage to skeletal muscle that negatively affected the early larval development of O. niloticus.

Study of Some Histological Properties of Skeletal Muscles in a Fish Gymnura micrura

The present study showed some histological properties of skeletal muscles in Gymnura micrura belong to the family Dasyatidae, specimens of fish collected from the AL-Fao area in Iraqi territorial waters with assistance from a fisherman. The results declare two types of cartilage that can be distinguished: hyaline cartilage, which constitutes a large percentage of the cartilage mass, in addition to the presence of another type, the elastic cartilage. The results showed that the diameter of red muscle fibers alternated between (22.30 - 37.17 microns), while it alternated between (44.61 – 104.09 microns) of the white muscle fibers diameter in studied fish, this difference possibly attributed to the functional role of white and red muscle fibers and their effect in the mechanics of movement.

Muscle bioenergetics of two emblematic Mediterranean fish species: Sardina pilchardus and Sparus aurata

We investigated links between swimming behavior and muscle bioenergetics in two emblematic Mediterranean fish species that have very different ecologies and activity levels. European sardines Sardina pilchardus are pelagic, they swim aerobically, school constantly and have high muscle fat content. Gilthead seabream Sparus aurata are bentho-pelagic, they show discontinuous spontaneous swimming patterns and store less fat in their muscle. Estimating the proportion of red and white muscle phenotypes, sardine exhibited a larger proportion of red muscle (~10% of the body mass) compared to gilthead seabream (~5% of the body mass). We firstly studied red and white muscle fiber bioenergetics, using high-resolution respirometers, showing a 4-fold higher oxidation capacity for red compared to white muscle. Secondly, we aimed to compare the red muscle ability to oxidize either lipids or carbohydrates. Sardine red muscle had a 3-fold higher oxidative capacity than gilthead seabream and a greater capacity to oxidize lipids. This study provides novel insights into physiological mechanisms underlying the different lifestyles of these highly-prized species.

Sustained Swimming Training Is Associated With Reversible Filet Texture Changes of European Sea Bass (Dicentrarchus labrax L.).

This present study aimed to investigate the effect of training and detraining on the growth, chemical composition, white muscle fibers, and filet texture of the European sea bass (Dicentrarchus labrax L.). Fish were divided into control and training groups, which were subjected to water velocities of 0.2 and 1.0 body length per second (bl s−1), respectively, for 32 days (phase I). Half of the fish in the training group were then randomly selected and detrained at a velocity of 0.2 bl s−1 for another 32 days (detraining group), while the velocity of the remaining fish in the training group (1 bl s−1), and control group (0.2 bl s−1) remained unchanged (phase II). The results showed that the growth, body composition, and white muscle fiber densities of the control and trained fish were not significantly different in either phase. Training significantly altered the muscle fiber distribution (P < 0.05), with the training group having fewer 80–90 μm fibers than the control and detraining group at the end of the experiment (P < 0.05). The training group also had significantly higher values for white fiber muscle textural parameters (hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness) in phase I (P < 0.05), and these parameters correlated significantly with pH (P < 0.05). However, these differences in texture and the pH correlation weakened when the fish were detrained in phase II. These results indicated that an increase in muscle pH after training may alter the flesh texture characteristics of sea bass. In addition, sustained swimming could induce a reversible change in the filet texture of sea bass.

1947-P: Comparative Effects of PCSK9 Inhibitor and High-Dose Atorvastatin on Mitochondria of Red Muscle Fibers in Obese Female Rats

Obesity and dyslipidemia cause mitochondrial dysfunction of skeletal muscle. Low dose atorvastatin impairs mitochondrial function of white muscle fibers but does not damage that of red muscle fibers. However, the effects of PCSK9 inhibitors and high dose atorvastatin on mitochondrial function of red muscle fibers have not been identified. Twenty-four female rats (180-200 g) were divided into 2 groups. Six rats were fed with normal diet (ND) and 18 rats were fed with high-fat diet (HFD) for 15 weeks. At week 12, ND-fed rats were treated with vehicle (NDV), while HFD-fed rats were equally subdivided and treated with either vehicle (HFV), 4 mg/kg/day of PCSK9 inhibitor (HFP), or 40 mg/kg/day of atorvastatin (HFA) for another 3 weeks. HFV rats developed obesity and dyslipidemia, as indicated by increased weight, visceral fat, and total cholesterol. Treatment with atorvastatin and PCSK9 inhibitor improved obesity and dyslipidemia. Increased lipid peroxidation (MDA), mitochondrial fission (pDrp1/Drp1), mitochondrial ROS production, and mitochondrial membrane depolarization were found in soleus muscle of HFV rats. Treatment with atorvastatin and PCSK9 inhibitor similarly improved lipid peroxidation and mitochondrial fission. However, only PCSK9 inhibitor improved mitochondrial ROS production and mitochondrial membrane depolarization. Our findings suggest that obesity increases lipid peroxidation, mitochondrial fission, mitochondrial ROS production, and mitochondrial membrane depolarization in red muscle fibers. PCSK9 inhibitor attenuates those deleterious effects of obesity. High dose atorvastatin improves lipid peroxidation and mitochondrial fission, but does not attenuate obesity-induced mitochondrial ROS production and mitochondrial membrane depolarization in red muscle fibers. The results imply that high dose atorvastatin causes adverse effects on red muscle fibers despite its benefit on the improvement of obesity and dyslipidemia. Disclosure C. Thonusin: None. S. Palee: None. B. Arunsak: None. P. Amput: None. W. Pratchayasakul: None. N. Chattipakorn: None. S.C. Chattipakorn: None. Funding Thailand Research Fund

Muscle growth mechanisms in response to isoenergetic changes in dietary non-protein energy source at low and high protein levels in juvenile rainbow trout

This study investigates muscle growth mechanisms in juvenile rainbow trout in response to isoenergetic changes in dietary non-protein energy (NPE) source (F, fat vs. C, carbohydrates) at two levels of digestible protein to digestible energy (DP/DE) ratio. Fish (initial weight 32.4 g) were fed four diets having similar DE levels (~18 kJ g−1) with a high (HP/E~26 mg kJ−1) vs. low (LP/E~14 mg kJ−1) DP/DE ratio using F or C as major NPE source (7 week-experiment). The lowering of dietary DP/DE ratio increased myoblast determination protein 1a (myod1a) and decreased myostatin 1b (mstn1b) and cathepsin D (ctsd) muscle mRNA levels. The isoenergetic change in dietary NPE from F to C decreased myod1a and proliferative cell nuclear antigen (pcna) muscle mRNA levels. An interaction between DP/DE ratio and NPE source was observed in muscle transcript levels of myogenic factor 6 (mrf4/myf6), fast myosin heavy chain (fmhc) and fast myosin light chain 2 (fmlc2). White muscle total cross-sectional area decreased at low dietary DP/DE ratio and also when NPE source changed from F to C, linked i) to a decreased total number of white muscle fibres, indicating that low dietary DP/DE restricted muscle hyperplasia and that dietary carbohydrate were less efficiently used than fat to sustain muscle hyperplasia, and ii) to decreased percentage of large muscle fibres, indicating limited fibre hypertrophy. Not only the DP level or the DP/DE ratio, but also the isoenergetic change in dietary NPE source (fat vs carbohydrates) thus appears as a potent regulator of muscle hyperplasia and hypertrophy.

Influence of β-Hydroxy-β-methylbutyrate on predominantly white and red muscles of rats not submitted to physical exercise

This study evaluated the influence of β-hydroxy-β-methylbutyrate (HMB) on the body weight and morphometry of white and red muscle fibers of sedentary rats. 29 male rats were divided in: initial control group (ICG ) (n = 5), euthanized at study onset, and three treated groups (n = 8 each): placebo control group (PCG) received saline for 4 weeks; experimental group (EG) received 0.3 g kg -1 of HMB daily and controlled diet; and experimental group ad libitum , (EGA) received 0.3g kg -1 of HMB daily, without food restriction. There was no difference in food intake and body weight between treated groups. For the EDL muscle, treated groups were different from ICG. Concerning the soleus muscle, no treated group was different from each other and only the EGA presented difference compared to the ICG. Data also did not reveal correlation between the variables food intake and body weight. HMB did not change the body weight or morphometry of EDL muscle fibers. However, the HMB combined with ad libitum feeding was able to change the morphometry of soleus muscle fibers.

The effect of water temperature on muscle cellularity and gill tissue of larval and juvenile Lophiosilurus alexandri, a Neotropical freshwater fish

The effect of temperature on muscle development and gill tissue were investigated in larval and juvenile of Lophiosilurus alexandri, a carnivorous Neotropical fish species. Larvae and juveniles were reared at temperatures of 23, 26, 29 and 32 °C for 15 and 35 days, respectively. The larvae were fed Artemia nauplii, while the juveniles received a formulated diet. In both stages, high temperatures resulted in increased fiber diameter of white muscle. Moreover, a pronounced effect of hypertrophy was observed in later stages of development. No alterations to minimum fiber diameter, and similar mosaic standards of muscle growth dynamics, were observed in larvae kept at 23–32 °C, suggesting that hyperplasia was not effected during early stages of development. Gills were analyzed by Degree of Tissue Change (DTC), which is based on the severity of lesions. Significant morphological changes were observed in gills when juveniles were kept at 32 °C, which was considered moderate tissue damage. Temperature modulates cellularity in L. alexandri larvae and juveniles, with pronounced alterations of hypertrophy of white muscle fibers in later stages of development when exposed to elevated temperatures. Higher temperatures may also induce muscle growth dynamics with increased recruitment of new white fiber, increased fiber diameter in the early stages and induced gill lesions.

Cannibalism, growth performance, and body composition of giant trahira juveniles under different photoperiods

Abstract: The objective of this work was to determine the effect of photoperiod on the cannibalism, growth, and body composition of giant trahira (Hoplias intermedius) juveniles. A completely randomized design was employed, with four photoperiods - 0L:24D, 6L:18D, 12L:12D, and 18L:6D, hours of light (L): dark (D) - and four replicates, for a period of 90 days. The analyzed parameters were: cannibalism, growth in weight and length, food consumption, feed conversion, protein efficiency rate, muscle growth, and body composition (moisture, lipid, ash, and crude protein). Fish from the 12L:12D photoperiod showed the highest survival rate and no cannibalism, as well as a great uniformity for length and mass values at the end of the experiment. The best photoperiod for giant trahira juveniles is 12L:12D, as these fish showed growth uniformity and no cannibalism, while fish from the 6L:18D and 18L:6D groups had a greater diameter of white muscle fibers and a higher frequency of greater diameter fibers. Giant trahira showed the lowest value for lipids at 6L:18D and the highest value at 12L:12D. Photoperiod affects survival and cannibalism; regarding body composition, only lipids are influenced by photoperiod.

&lt;b&gt;Influence of rearing temperature on muscle growth and adipose tissue in Nile tilapia (&lt;i&gt;Oreochromis niloticus&lt;/i&gt;) strains

This study aimed to evaluate the effect of temperature on the tissue growth of Red, GIFT and Supreme tilapia strains. Fingerlings of approximately 1.4 g from male populations were reared for a period of 60 days, in three recirculating systems, each system containing 6 water tanks of 0.5 m³, at three temperatures (22, 28 and 30ºC). Ten fish of each recirculation system and each temperature studied were sampled. Fishes have been anesthetized, euthanized and weighed. The samplings have been done from the dorsal musculature, caudal, visceral and ventral subcutaneous adipose tissue. Histological sections were prepared and evaluated to determine the diameter of the cells. The experimental design was completely randomized factorial 3 X 3 (strain X temperature). Analysis of variance was performed and means were compared. Higher weights were found for fish reared at 30°C (56.23 g) compared to those grown at 28 (42.12 g) or 22°C (10.52 g). The cooled water temperature (22°C) may have contributed to the hypertrophy of white muscle fibers and visceral adipocytes from tilapia, compared to 28 or 30ºC. Red Tilapia, GIFT and Supreme strains show differences in muscle growth and adipose tissues in response to temperature of cultivation.

Influence of rearing temperature on muscle growth and adipose tissue in Nile tilapia (Oreochromis niloticus) strains

This study aimed to evaluate the effect of temperature on the tissue growth of Red, GIFT and Supreme tilapia strains. Fingerlings of approximately 1.4 g from male populations were reared for a period of 60 days, in three recirculating systems, each system containing 6 water tanks of 0.5 m³, at three temperatures (22, 28 and 30oC). Ten fish of each recirculation system and each temperature studied were sampled. Fishes have been anesthetized, euthanized and weighed. The samplings have been done from the dorsal musculature, caudal, visceral and ventral subcutaneous adipose tissue. Histological sections were prepared and evaluated to determine the diameter of the cells. The experimental design was completely randomized factorial 3 X 3 (strain X temperature). Analysis of variance was performed and means were compared. Higher weights were found for fish reared at 30°C (56.23 g) compared to those grown at 28 (42.12 g) or 22°C (10.52 g). The cooled water temperature (22°C) may have contributed to the hypertrophy of white muscle fibers and visceral adipocytes from tilapia, compared to 28 or 30oC. Red Tilapia, GIFT and Supreme strains show differences in muscle growth and adipose tissues in response to temperature of cultivation.

Aerobic exercise training rescues protein quality control disruption on white skeletal muscle induced by chronic kidney disease in rats.

We tested whether aerobic exercise training (AET) would modulate the skeletal muscle protein quality control (PQC) in a model of chronic kidney disease (CKD) in rats. Adult Wistar rats were evaluated in four groups: control (CS) or trained (CE), and 5/6 nephrectomy sedentary (5/6NxS) or trained (5/6NxE). Exercised rats were submitted to treadmill exercise (60 min., five times/wk for 2 months). We evaluated motor performance (tolerance to exercise on the treadmill and rotarod), cross‐sectional area (CSA), gene and protein levels related to the unfolded protein response (UPR), protein synthesis/survive and apoptosis signalling, accumulated misfolded proteins, chymotrypsin‐like proteasome activity (UPS activity), redox balance and heat‐shock protein (HSP) levels in the tibialis anterior. 5/6NxS presented a trend towards to atrophy, with a reduction in motor performance, down‐regulation of protein synthesis and up‐regulation of apoptosis signalling; increases in UPS activity, misfolded proteins, GRP78, derlin, HSP27 and HSP70 protein levels, ATF4 and GRP78 genes; and increase in oxidative damage compared to CS group. In 5/6NxE, we observed a restoration in exercise tolerance, accumulated misfolded proteins, UPS activity, protein synthesis/apoptosis signalling, derlin, HSPs protein levels as well as increase in ATF4, GRP78 genes and ATF6α protein levels accompanied by a decrease in oxidative damage and increased catalase and glutathione peroxidase activities. The results suggest a disruption of PQC in white muscle fibres of CKD rats previous to the atrophy. AET can rescue this disruption for the UPR, prevent accumulated misfolded proteins and reduce oxidative damage, HSPs protein levels and exercise tolerance.

Alteration in expression of atrogenes and IGF-1 induced by fasting in Nile tilapia Oreochromis niloticus juveniles

The growth rate of farmed fish is an important factor regarding aquaculture success. An understanding of the cellular events that occur in skeletal muscle when fish undergo periods of fasting and refeeding provides information useful in developing alternative feeding strategies for improving muscle growth in commercially cultivated species. To evaluate the effect of 1–3 weeks of fasting and 10 weeks of refeeding in Nile tilapia juveniles, we analyzed the growth performance and changes in muscle cellularity and the expression of the following growth and muscle related genes: MyoD, myogenin, IGF-1, IGF-1 receptor, MuRF-1, atrogin-1 and myostatin. Reduced body mass was observed in all three groups of fasted fish during their time off feed, and 10 weeks of refeeding resulted in partial compensatory growth of body mass. No differences in the frequency of white muscle fiber diameters were observed between fasted and fed control fish treatments. However, changes in gene expression induced by fasting and refeeding were found. IGF-1 receptor, ubiquitin ligases MuRF1 and atrogin-1 expression increased during the 1–3 weeks of fasting, while IGF-1 levels dropped significantly (P < 0.001) compared to the control treatment. Furthermore, myogenin mRNA level in fish submitted to 3 weeks of fasting was higher in comparison to the control treatment (P < 0.05). Overall, our results showed that 1–3 weeks of fasting can induce muscle atrophy activation in Nile tilapia juveniles, and 10 weeks of refeeding is enough to induce only partial compensatory growth.

Effect of dietary methionine level on muscle growth mechanisms in juvenile rainbow trout (Oncorhynchus mykiss)

The aim of the study was to analyse the effects of different dietary methionine (Met) concentrations on the mechanisms of fish muscle growth (hyperplasia and hypertrophy) by using cellular and molecular approaches. Three plant-based diets differing by their Met level (MD, Met-deficient; MC, Met-control, corresponding to established Met requirement; MH, Met-high) were fed to rainbow trout juveniles for 12weeks. Met deficiency led to a reduced somatic growth right from the first 3weeks of feeding onwards, while feeding the MH-diet led to an increased body growth in the 6 last weeks of feeding. The protein gain of the juveniles increased with dietary Met content. The protein retention efficiency of the MD-fed juveniles was half that of the MC- and MH-fed juveniles which were statistically similar. The changes induced by MD- and MH-feeding at muscle molecular and cellular levels were different. Compared to control, dietary Met deficiency altered the expression of myogenic, muscle growth- and metabolism-related genes by increasing Myf5, MyoD1, Mrf4, Mef2a, βact, CathD, GSTπ and TNFα expressions and decreasing Col1α1 and IGF1 expressions, whereas a high level of dietary Met decreased Pax7a2, Mef2c, βact, CathD, GDH2 and NF-κB expressions. The Met-control fed fish were discrimated according to HGF, Pax7a1 and Pax7a2 expressions. Dietary Met level thus acted on the expression of genes regulating specific transition points of myogenesis, and affected the expression of muscle structural genes and growth factors involved in satellite cell activation and muscle growth. Molecular results suggested that MD-diet favours satellite cell return to quiescence, while MC-diet favours satellite cell activation and MH-diet myogenic differentiation. At cellular level, the muscle total cross-sectional area of the juveniles fed the MD-diet was 28% lower than that of the juveniles fed the MC-diet despite a similar total number of white muscle fibres, and the number of white muscle fibres with a large diameter was lower in MD-fed fish than in MC-fed ones. The muscle total cross-sectional area of the juveniles fed the MH-diet was 32% higher than that of the juveniles fed the MC-diet, their total number of white muscle fibres 25% higher, and their number of white muscle fibres with a large diameter similar. Increasing dietary methionine above established requirement thus promotes white muscle hyperplasia and muscle growth in rainbow trout juveniles, while methionine deficiency dysregulates the expression of myogenic and muscle growth-related genes and impairs white fibre hypertrophy. Statement of relevanceDetermining the effects of dietary methionine levels on muscle growth mechanisms will help develop low fish meal feeds.

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.

Genetic background and embryonic temperature affect DNA methylation and expression of myogenin and muscle development in Atlantic salmon (Salmo salar).

The development of ectothermic embryos is strongly affected by incubation temperature, and thermal imprinting of body growth and muscle phenotype has been reported in various teleost fishes. The complex epigenetic regulation of muscle development in vertebrates involves DNA methylation of the myogenin promoter. Body growth is a heritable and highly variable trait among fish populations that allows for local adaptations, but also for selective breeding. Here we studied the epigenetic effects of embryonic temperature and genetic background on body growth, muscle cellularity and myogenin expression in farmed Atlantic salmon (Salmo salar). Eggs from salmon families with either high or low estimated breeding values for body growth, referred to as Fast and Slow genotypes, were incubated at 8°C or 4°C until the embryonic ‘eyed-stage’ followed by rearing at the production temperature of 8°C. Rearing temperature strongly affected the growth rates, and the 8°C fish were about twice as heavy as the 4°C fish in the order Fast8>Slow8>Fast4>Slow4 prior to seawater transfer. Fast8 was the largest fish also at harvest despite strong growth compensation in the low temperature groups. Larval myogenin expression was approximately 4–6 fold higher in the Fast8 group than in the other groups and was associated with relative low DNA methylation levels, but was positively correlated with the expression levels of the DNA methyltransferase genes dnmt1, dnmt3a and dnmt3b. Juvenile Fast8 fish displayed thicker white muscle fibres than Fast4 fish, while Slow 8 and Slow 4 showed no difference in muscle cellularity. The impact of genetic background on the thermal imprinting of body growth and muscle development in Atlantic salmon suggests that epigenetic variation might play a significant role in the local adaptation to fluctuating temperatures over short evolutionary time.