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In this study, selectively bred rainbow trout (Oncorhynchus mykiss) with improved fillet yield were reared on three commercially available diets that varied in dietary lipid content: low lipid (LL, 18%), moderate lipid (ML, 24%), and high lipid (HL, 29%–33%). The objective was to determine if a genotype by diet interaction affects product yield and muscle quality traits in high fillet yield (HY) and low fillet yield (LY) lines of rainbow trout. Main effects of the genetic line (p < 0.05) were observed for viscera yield, carcass yield, and fillet yield that were more favorable in the HY line. Analysis of muscle quality traits indicated that selection for fillet yield did not compromise fillet quality. A genotype by diet interaction (p < 0.05) was observed for viscera lipid content at the 2 kg harvest, for which viscera lipid content was similar between the HY and LY lines for the LL and HL diets, but greater (p < 0.05) in the LY line for the ML diet. Collectively, these findings indicate that higher product yields in the selectively bred HY line of rainbow trout will persist across diets with variable crude lipid/energy contents. [ABSTRACT FROM AUTHOR]

Previous studies have shown that Nannochloropsis gaditana can partially replace fishmeal in the diet of gilthead seabream, Sparus aurata. However, its effect on muscle growth is hardly known. This experiment was carried out with gilthead seabream adults that were fed with N. gaditana at two inclusion levels (2.5 or 5%) either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups) for 45 days in the final fattening phase. The body length and body weight were measured in all fish at the beginning and end of the experiment. Also, the white muscle transverse area (WM), size, number and fibrillar density of the white fibers were measured in 9 fish group−1. After 45 days, the body parameters and the WM did not show significant differences among the groups. However, muscle cellularity did show significant differences, such that the hypertrophy values were higher in the H2.5 and H5 than in the R2.5 and R5 groups. On the contrary, R2.5 and R5 showed the highest fibrillar density and hyperplasia values, which are often positively correlated with the fillet firmness and therefore could improve the final quality of the fish. No significant differences attributable to the inclusion levels of N. gaditana were observed. [ABSTRACT FROM AUTHOR]

Simple Summary: Currently, microalgae are used as a partial substitute for fishmeal and fish oil in fish diets, but it is unknown if this can influence the long-term growth of the fish. In the present work, we have studied the long-term effects of diets enriched with the microalgae Nannochloropsis gaditana that were supplied to juvenile gilthead seabream, Sparus aurata, at two inclusion levels (2.5 and 5%), either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups), for three months. Subsequently, all groups were transferred to a microalgae-free diet until commercial size was reached (1.6-year-old, ≈27 cm and ≈300 g). The results showed that three-month microalgae supplementation of the diets in juvenile fish had a long-term influence on the final body and muscle growth, as well as in the fibrillar constitution of the myotome. This influence depended on the state (raw versus hydrolyzed) and the microalgae inclusion levels in the diet, in such a way that the hydrolyzed diet mainly increased muscle growth and hyperplasia of the specimens, and this was greater at higher inclusion levels. The fact that microalgae inclusion in the juvenile diet can improve subsequent growth may be advantageous for fish farmers. Currently, microalgae are used in fish diets, but their long-term growth effect is unknown. In this experiment, juvenile seabream specimens were fed with microalgae-enriched diets for three months, and then transferred to a microalgae-free diet for 10 months to assess long-term effects up to commercial size (≈27 cm and ≈300 g). The juvenile diets contained Nannochloropsis gaditana at 2.5 or 5% inclusion levels, either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups). The body length and weight were measured in 75 fish group−1 at commercial stage. The size, number, and fibrillar density of white muscle fibers and the white muscle transverse area were measured in nine fish group−1 at commercial stage. The results showed the highest body weight in H5 at commercial stage. The white muscle transverse area and the white fibres hyperplasia and density also showed the highest values in H5, followed by H2.5. In contrast, the highest hypertrophy was observed in C and R2.5, being associated with the lowest muscle growth in both groups. These results showed a microalgae concentration-dependent effect in hydrolyzed diets as well as an advantageous effect of the hydrolyzed versus raw diets on the long-term growth of Sparus aurata. [ABSTRACT FROM AUTHOR]

Dietary supplementation with hydrolysates has been suggested to influence muscle protein synthesis and fish growth. This study assessed the impact of including 3% swine blood hydrolysates (BH) in a plant-based diet on muscle cellularity and the expression of molecular markers related to muscle fibre proliferation and hypertrophic growth of European seabass. Three BH fractions were obtained by two different processes, autohydrolysis (AH-H) and enzymatic hydrolysis followed by micro- (RMF-H) and nanofiltration (RNF-H). Each BH was added to a commercial-based diet, where 50% of fishmeal was replaced by vegetable proteins (negative control, NC). A fishmeal-based diet was used as positive control, PC. The diets were fed to juveniles (12 g) during 74 days. The RMF group showed down-regulation of myod1 and fgf4, essential to myoblast proliferation and differentiation, and upregulation of mafbx, responsible for protein breakdown, resulting in impairment of muscle hyperplasic growth and the lowest muscle fibres number. However, compensatory growth mechanisms were observed through capn1 downregulation and mymk upregulation, suggesting decreased muscle proteolysis and increased myoblast fusion. Despite this, the compensatory mechanisms were insufficient as RMF group had the worst growth. RNF group had a final weight similar to the NC, but downregulation of fgf4, fgf6 and capn1 may compromise growth potential at long term. The expression of these genes in the AH group was similar to that in the FM-based diet. Despite not having demonstrated growth promotion ability, BH affect muscle growth and cellularity factors, prompting further research on commercial-sized fish to reveal their impact on important commercial traits.

Previous studies have shown that Nannochloropsis gaditana can partially replace fishmeal in the diet of gilthead seabream, Sparus aurata. However, its effect on muscle growth is hardly known. This experiment was carried out with gilthead seabream adults that were fed with N. gaditana at two inclusion levels (2.5 or 5%) either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups) for 45 days in the final fattening phase. The body length and body weight were measured in all fish at the beginning and end of the experiment. Also, the white muscle transverse area (WM), size, number and fibrillar density of the white fibers were measured in 9 fish group−1. After 45 days, the body parameters and the WM did not show significant differences among the groups. However, muscle cellularity did show significant differences, such that the hypertrophy values were higher in the H2.5 and H5 than in the R2.5 and R5 groups. On the contrary, R2.5 and R5 showed the highest fibrillar density and hyperplasia values, which are often positively correlated with the fillet firmness and therefore could improve the final quality of the fish. No significant differences attributable to the inclusion levels of N. gaditana were observed.

Methionine and taurine are amino acids (AA) that are usually deficient when fish meal is replaced by plant proteins. In this study, three diets were tested in juvenile meagre (initial weight: 13.4 g) for 8 weeks. The D1 diet had 0.2% methionine and 1% taurine supplementation; the D2 and D3 diets had 0.6% methionine and 1% and 2% taurine supplementation, respectively. The results showed that meagre fed the D1 diet had lower specific growth rate (2.2 to 2.5), lower feed efficiency (0.9 to 1.2) and higher food conversion rate (FCR, 1.1 to 0.8) as well as a lower activity of the alanine aminotransferase (ALAT) enzyme. Furthermore, a higher recruitment of muscle fibres (46% compared to 36%) as well as a higher fibre density was observed (1019 compared to 870 fibres mm–2). This study shows that meagre requires a sufficient quantity of methionine in plant‐based diets to avoid a reduction in fish performance. Furthermore, taurine supplementation in the D1 diet was not able to mitigate the effects of methionine deficiency. A higher taurine supplementation did not improve meagre performance. [ABSTRACT FROM AUTHOR]

Currently, microalgae are used in fish diets, but their long-term growth effect is unknown. In this experiment, juvenile seabream specimens were fed with microalgae-enriched diets for three months, and then transferred to a microalgae-free diet for 10 months to assess long-term effects up to commercial size (≈27 cm and ≈300 g). The juvenile diets contained Nannochloropsis gaditana at 2.5 or 5% inclusion levels, either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups). The body length and weight were measured in 75 fish group−1 at commercial stage. The size, number, and fibrillar density of white muscle fibers and the white muscle transverse area were measured in nine fish group−1 at commercial stage. The results showed the highest body weight in H5 at commercial stage. The white muscle transverse area and the white fibres hyperplasia and density also showed the highest values in H5, followed by H2.5. In contrast, the highest hypertrophy was observed in C and R2.5, being associated with the lowest muscle growth in both groups. These results showed a microalgae concentration-dependent effect in hydrolyzed diets as well as an advantageous effect of the hydrolyzed versus raw diets on the long-term growth of Sparus aurata.

Seven-month-old shi drum (Umbrina cirrosa) specimens (mean weight 18.98 g, mean length 11.80 cm) were classified into 2 groups, a control group (C) fed a standard diet and a vegetal group (V) fed a diet with partial replacement of fish meal and fish oil by vegetable products. The body and muscle parameters were studied on days 0, 27, and 62 of the experiment. On day 27, body length was similar in both groups, but body weight was significantly lower in group V than in group C. The transverse area of the white muscle was also significantly lower in V than in C. Hypertrophy was higher in C than in V, whereas hyperplasia was higher in V than in C. On day 62, the body parameters showed similar results to those found on day 27. Muscle cellularity was different from that found on day 27, since hypertrophy was higher in V than in C and hyperplasia was higher in C than in V. The feed conversion rate and specific growth rate were similar in both groups, but the daily intake rate was lower in V than in C. Therefore, it seems that the percentage of vegetables in the vegetal feed was excessively high and this caused less acceptance by the fish. The hepatosomatic, viscerosomatic, and intestinal length indices were similar in both groups. Survival was nearly 100% in both groups.

Endocrine-disrupting chemicals include natural and synthetic estrogens, such as 17α-ethynilestradiol (EE2), which can affect reproduction, growth and immunity. Estrogen signalling is mediated by nuclear or membrane estrogen receptors, such as the new G-protein-coupled estrogen receptor 1 (GPER1). The present work studies the effect of EE2 and G1 (an agonist of GPER1) on body and muscle parameters and growth-related genes of 54 two-year-old seabreams. The fish were fed a diet containing EE2 (EE2 group) and G1 (G1 group) for 45 days and then a diet without EE2 or G1 for 122 days. An untreated control group was also studied. At 45 days, the shortest body length was observed in the G1 group, while 79 and 122 days after the cessation of treatments, the shortest body growth was observed in the EE2 group. Hypertrophy of white fibers was higher in the EE2 and G1 groups than it was in the control group, whereas the opposite was the case with respect to hyperplasia. Textural hardness showed a negative correlation with the size of white fibers. At the end of the experiment, all fish analyzed in the EE2 group showed a predominance of the gonadal ovarian area. In addition, the highest expression of the mafbx gene (upregulated in catabolic signals) and mstn2 (myogenesis negative regulator) was found in EE2-exposed fish.

Histidine plays an important role in haemoglobin synthesis, antioxidant defence system and stress resistance, and it is thought to be a limiting amino acid in most meagre diets. In this study, two different diets, a control and a diet supplemented with 3% histidine, were tested in 60‐day‐old meagre (initial weight—6.2 g) for 82 days. Survival varied between 92% and 94%, and neither SGR nor whole fish composition seemed to be affected by the diet. When fish were submitted to a stress test (outside water for 30 s), it was observed that the levels of glucose and lactate significantly increased in both treatments. The concentration of cortisol increased after the stress test only in the His 30 g/kg group. Muscle cellularity was affected by the diets, where the control group showed a higher mean fibre area and lower fibre density. These results, associated with a lower frequency of smaller fibres, suggest a decrease in fibre recruitment and a higher fibre hypertrophy. In conclusion, the supplementation of diets with 3% led to a more pronounced response to the stress test in terms of cortisol levels and increased muscle fibre recruitment, decreasing muscle fibre hypertrophy contribution to muscle growth. [ABSTRACT FROM AUTHOR]

During the past 20 years, plant ingredients have taken over as the main constituents in feed for Atlantic salmon. This has changed the nutrient composition of the feeds, the bioavailability of nutrients and perhaps nutrient metabolism. Plant‐based diets also contain more anti‐nutrients. The EU‐funded project ARRAINA re‐evaluated recommendations for micronutrient supplementation to Atlantic salmon feeds, and the present study compared a diet supplemented with micronutrients according to NRC (2011) (control diet, 100% NP (nutrient package)) with a diet supplemented according to the new recommendations (New NP). Tissue concentrations of pyridoxine, pantothenic acid, niacin, vitamin C, Zn and Se were significantly higher; and Cu was lower in Atlantic salmon fed the diet with the New NP compared to the control fish. The New NP also gave a near significant effect on growth, decreased muscle firmness and increased muscle cell size, and it affected metabolism of nitrogen‐containing metabolites in the muscle. While we cannot be certain which micronutrient(s) gave these effects, the B vitamins are probable candidates, since they are mediators of intermediary metabolism and have been shown to influence some of the affected metabolites. [ABSTRACT FROM AUTHOR]

Seven-month-old shi drum (Umbrina cirrosa) specimens (mean weight 18.98 g, mean length 11.80 cm) were classified into 2 groups, a control group (C) fed a standard diet and a vegetal group (V) fed a diet with partial replacement of fish meal and fish oil by vegetable products. The body and muscle parameters were studied on days 0, 27, and 62 of the experiment. On day 27, body length was similar in both groups, but body weight was significantly lower in group V than in group C. The transverse area of the white muscle was also significantly lower in V than in C. Hypertrophy was higher in C than in V, whereas hyperplasia was higher in V than in C. On day 62, the body parameters showed similar results to those found on day 27. Muscle cellularity was different from that found on day 27, since hypertrophy was higher in V than in C and hyperplasia was higher in C than in V. The feed conversion rate and specific growth rate were similar in both groups, but the daily intake rate was lower in V than in C. Therefore, it seems that the percentage of vegetables in the vegetal feed was excessively high and this caused less acceptance by the fish. The hepatosomatic, viscerosomatic, and intestinal length indices were similar in both groups. Survival was nearly 100% in both groups. [ABSTRACT FROM AUTHOR]

The muscle and textural parameters were analyzed in four myotome zones (epaxial upper, hipoaxial upper, epaxial bottom, and hipoaxial bottom) in seven diploids (D) and seven triploids (T) turbot specimens. Diploid specimens showed the highest values of the size and number of white fibers in the epaxial zones, being such values higher in female than male specimens. In triploid specimens, the highest fibers sizes were found in the upper zones (epaxial and hipoaxial), whereas the lowest number and density of fibers were found in the epaxial upper zone. In this latter group (T), the lowest fibers sizes were found in female specimens, whereas the rest of the parameters were usually higher in female than male specimens. When comparing both groups, the hypertrophy was higher in T than D in all zones. In both ploidy groups, the highest textural values were usually observed in the upper epaxial fillet, being slightly higher in female than male specimens. The values of standard length, total weight, gonad weight, gonadosomatic index and gutted weight were higher in female than male specimens in both groups (D and T). [ABSTRACT FROM AUTHOR]

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.

This study assessed cellular characteristics of longissimus lumborum (LL) and semitendinosus (ST) muscles in steers genetically selected for low (Low) or high (High) muscling using live muscle scoring, and High steers with 1 copy of the loss-of-function 821 del11 MSTN allele (HighHet). We hypothesized High and HighHet have altered muscle cellular characteristics and mechanisms influencing muscling compared with Low steers. Angus steers 25 mo old comprising 14 High, 19 Low, and 11 HighHet were backgrounded to 20 mo of age, grain finished for 150 d, and then slaughtered. Body and carcass weights did not differ due to muscling line (P = 0.46). Weight of LL was 16% greater (P = 0.004) and total protein in LL was 18% greater (P = 0.012) in HighHet than Low steers. ST weight in HighHet was 10% and 13% greater than in High and Low steers (P = 0.007), respectively, and of total ST protein 12% and 17% greater in HighHet than High or Low (P = 0.002). Cross-sectional area (CSA) of LL was greater in HighHet than in High and greater in High than in Low (85.0 vs. 77.0 vs. 70.4 cm2, P < 0.001). Apparent number of myofibers and myofibers per unit CSA did not differ between the muscling lines in LL (P = 0.14) or ST (P = 0.47). Myofiber CSA was greater in the ST of Low than of High and HighHet for type 1 (36% and 31% respectively, P = 0.005) and 2A (22% and 25%, P < 0.001). HighHet steers had greater area of glycolytic (type 2X) relative to more oxidative myofiber types within LL (P = 0.02; 11% and 43% more than High and Low, respectively) and ST (P < 0.001; 27% and 75%). Concentration of RNA in LL was 13% and 10% greater (P = 0.005) in High than in Low and HighHet, respectively, and total amount of RNA in LL was 22% greater in High and 20% greater in HighHet than in Low (P < 0.001). The LL of High steers had less protein to RNA (P = 0.03; 57.4 vs. 65.6) and more RNA to DNA (P = 0.007; 9.03 vs. 7.83) than Low. HighHet steers had 11% more DNA in ST than High (P = 0.04) and 19% more RNA in ST than Low (P = 0.012). The shift towards glycolytic myofibers was consistent with loadings in a principal component that explained 39% of the variation in LL and 38% in ST. Overall, these findings show that selection for increased muscling using live cattle muscle scoring, and 1 copy of the 821 del11 MSTN allele, results in more glycolytic muscle. They also suggest that increased muscling of the High compared with Low steers may be associated with increased translational capacity in the LL. [ABSTRACT FROM AUTHOR]

This study assessed cellular characteristics of longissimus lumborum (LL) and semitendinosus (ST) muscles in steers genetically selected for low (Low) or high (High) muscling using live muscle scoring, and High steers with 1 copy of the loss-of-function 821 del11 MSTN allele (HighHet). We hypothesized High and HighHet have altered muscle cellular characteristics and mechanisms influencing muscling compared with Low steers. Angus steers 25 mo old comprising 14 High, 19 Low, and 11 HighHet were backgrounded to 20 mo of age, grain finished for 150 d, and then slaughtered. Body and carcass weights did not differ due to muscling line (P = 0.46). Weight of LL was 16% greater (P = 0.004) and total protein in LL was 18% greater (P = 0.012) in HighHet than Low steers. ST weight in HighHet was 10% and 13% greater than in High and Low steers (P = 0.007), respectively, and of total ST protein 12% and 17% greater in HighHet than High or Low (P = 0.002). Cross-sectional area (CSA) of LL was greater in HighHet than in High and greater in High than in Low (85.0 vs. 77.0 vs. 70.4 cm2, P < 0.001). Apparent number of myofibers and myofibers per unit CSA did not differ between the muscling lines in LL (P = 0.14) or ST (P = 0.47). Myofiber CSA was greater in the ST of Low than of High and HighHet for type 1 (36% and 31% respectively, P = 0.005) and 2A (22% and 25%, P < 0.001). HighHet steers had greater area of glycolytic (type 2X) relative to more oxidative myofiber types within LL (P = 0.02; 11% and 43% more than High and Low, respectively) and ST (P < 0.001; 27% and 75%). Concentration of RNA in LL was 13% and 10% greater (P = 0.005) in High than in Low and HighHet, respectively, and total amount of RNA in LL was 22% greater in High and 20% greater in HighHet than in Low (P < 0.001). The LL of High steers had less protein to RNA (P = 0.03; 57.4 vs. 65.6) and more RNA to DNA (P = 0.007; 9.03 vs. 7.83) than Low. HighHet steers had 11% more DNA in ST than High (P = 0.04) and 19% more RNA in ST than Low (P = 0.012). The shift towards glycolytic myofibers was consistent with loadings in a principal component that explained 39% of the variation in LL and 38% in ST. Overall, these findings show that selection for increased muscling using live cattle muscle scoring, and 1 copy of the 821 del11 MSTN allele, results in more glycolytic muscle. They also suggest that increased muscling of the High compared with Low steers may be associated with increased translational capacity in the LL. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A 90-d feeding trial was conducted in which five groups of gilthead seabream (11.96 g initial body weight) were fed with a microalgae-free diet (control group, C) or four diets containing the microalgae Nannochloropsis gaditana at two inclusion levels (2.5% or 5%), either raw (R2.5 and R5 batches) or cellulose-hydrolyzed (H2.5 and H5 batches), to study their effect on the body and muscle growth. At 40 days, the highest values of body length and weight were reached in R5 group, but at 64 and 90 days, these were reached in R2.5. However, feed conversion rate, specific growth, daily intake, and survival (100%) were similar in all the groups. The acquisition of a discoid body shape was accelerated depending on the inclusion level of N. gaditana in the diets. Moreover, H5 diet affected the fish geometric morphology compared to R5 diet. The white muscle transverse area was similar in all groups at 40 days, with the exception of H2.5 group, which showed the lowest area. At day 90, C and R2.5 displayed the highest muscle growth, attributable to increased hyperplasia in C, and higher hypertrophy in R2.5. However, the highest proportion of small and medium fibers was observed in R5 and H5.

Abstract: In this study, two different dietary protein levels were tested (500 and 600 g/kg) in meagre juveniles of approximately 2 g, to determine whether a higher body protein diet would favour muscle growth. Results showed that meagre survival and growth were not affected by different levels of dietary protein. However, a higher content of protein was observed in the body composition of meagre fed the P60 diet (656 g/kg versus 624 g/kg). When fish were 82 days after hatched (DAH), protein retention efficiency was significantly higher in fish that were fed the P50 diet (37.1% versus 32.5%). Muscle cellularity changed considerably from the beginning to the end of the trial. The contribution of fibre hyperplasia to muscle growth was reduced although still accounted for 30% in 96 DAH meagre. Several differences were found in the frequency of fibres with areas between 1,000 μm2 and 2,200 μm2 between younger and older meagre, but no effect was found associated with dietary protein. This study suggests that neither growth nor muscle cellularity of fast‐growing juvenile meagre is positively affected by an increased dietary protein levels. [ABSTRACT FROM AUTHOR]

Abstract: Formulation of diets according to fish amino acid (AA) qualitative requirements may improve fish growth. Two diets with different AA profiles were tested on 16‐day‐old meagre during 20 days. The first diet had an AA profile closer to meagre larval AA requirements (BAL), whereas the second had a different AA profile (UNBAL). Results showed that larvae fed the diet with higher similarities to the AA profile of meagre carcass had a higher final weight (19.8 ± 0.5 mg versus 13.4 ± 1.8 mg) and lower ammonia excretion after being fed (0.6 ± 0.1 ml/(g DW. larvae. h) and 0.8 ± 0.1 ml/(g DW larvae. h)). A higher mean fibre area was obtained in 36 DAH larvae fed the BAL diet (224.8 ± 33.3 μm2 versus 158.8 ± 34.5 μm2) as well as higher larval weight. When fibre area distribution was analysed, a higher frequency of larger fibres was observed in 36 DAH BAL larvae, suggesting that fibre hypertrophy had a higher importance in this treatment. In conclusion, this study shows that meagre larvae fed a diet with an AA profile closer to their requirements had lower nitrogen losses and higher final weight, as result of higher muscle hypertrophy. [ABSTRACT FROM AUTHOR]

Meagre, Argyrosomus regius , is a promising new species for aquaculture due to its flesh quality, taste and growth performance in captivity. This study evaluated the quality of wild and farmed meagre in terms of flesh texture and nutritional profile. Texture traits were characterized using sensory analysis and instrumental measurements. Furthermore, muscle cellularity was analysed to determine potential relationships with flesh texture. Nutritional profile was evaluated focusing on protein and fat contents, as well as on fatty acid and amino acid profiles. Results showed that the most pronounced difference between wild and farmed meagre was the fat content, which was six times higher in the latter (3.93% versus 0.64%). This was reflected in a higher contribution of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), fulfilling completely the European Food Safety Authority (EFSA) recommendations in the case of farmed fish fillets (125% compared to 45% in farmed and wild meagre, respectively). Protein content was also higher in farmed fish (19.74% versus 17.18%) and amino acids scores were above 100% when compared to FAO/WHO amino acid standard. Raw fillet hardness was higher in wild meagre (96.05 N versus 60.35 N), but sensory analysis showed higher scores for firmness and oiliness in farmed fish. Muscle fibre density and area were similar in both wild and farmed meagre and therefore could not have been responsible for the differences found in fillet texture traits. In conclusion, this study shows that farmed meagre flesh may have some higher quality aspects in comparison to wild meagre and its overall attribute profile makes it an attractive food, thereby justifying its farming. [ABSTRACT FROM AUTHOR]

Thermoregulation in ectothermic animals is influenced by the ability to effectively respond to thermal variations. While it is known that ectotherms are affected by thermal changes, it remains unknown whether physiological and/or metabolic traits are impacted by modifications to the thermal environment. Our research provides key evidence that fish ectotherms are highly influenced by thermal variability during development, which leads to important modifications at several metabolic levels (e.g., growth trajectories, microstructural alterations, muscle injuries, and molecular mechanisms). In Atlantic salmon ( Salmo salar), a wide thermal range (ΔT 6.4°C) during development (posthatch larvae to juveniles) was associated with increases in key thermal performance measures for survival and growth trajectory. Other metabolic traits were also significantly influenced, such as size, muscle cellularity, and molecular growth regulators possibly affected by adaptive processes. In contrast, a restricted thermal range (ΔT 1.4°C) was detrimental to growth, survival, and cellular microstructure as muscle growth could not keep pace with increased metabolic demands. These findings provide a possible basic explanation for the effects of thermal environment during growth. In conclusion, our results highlight the key role of thermal range amplitude on survival and on interactions with major metabolism-regulating processes that have positive adaptive effects for organisms. [ABSTRACT FROM AUTHOR]

Production of triploid turbot is a relevant goal for the aquaculture industry due to the benefits associated with their sterility and growth. In order for a better understanding of the final quality of the species, muscle cellularity and quality parameters of the flesh were studied in seven diploid and seven triploid turbot after sexual maturation. White muscle cellularity was evaluated throughout white muscle cross-sectional area from the epaxial left muscle section of each fish. To ascertain the flesh quality, several physico-chemical parameters (moisture, ash, protein, total fat, fatty acids and minerals) were analysed, and textural mechanical properties (springiness, hardness, chewiness, cohesiveness, gumminess and adhesiveness) were determined objectively with a texturometer. Muscle cellularity was different between both groups, such that muscle fibre density was higher for diploid specimens ( P < 0.001) and muscle fibres diameters were higher for triploids ( P < 0.001). Both ploidy groups showed no significant differences in moisture, ash, protein and total fat content ( P > 0.05). All textural properties analysed showed no significant differences between both ploidy groups ( P > 0.05). In both ploidy groups, fibre density and fibre diameter showed no significant correlations ( P > 0.05) with textural parameters such as springiness, cohesiveness, chewiness and adhesiveness. Ploidy did not affect fatty acid composition, with the exception of eicosapentaenoic acid (C20:5ω3) which was higher in the triploid group. No significant differences ( P > 0.05) existed between diploid and triploid turbot in content of all minerals analysed. According to our results, the ploidy status determines significant variations on muscle cellularity but does not influence the flesh quality of the turbot. [ABSTRACT FROM AUTHOR]

Shi drum ( Umbrina cirrosa L.) larvae were maintained under three photoperiod regimes: a natural photoperiod regime (16L:8D), continuous light (24L) and equal durations of light and dark (12L:12D) from the end of the vitelline phase to the end of the metamorphosis. Muscle and body parameters were studied at hatching and at 4, 10, 14, 39 and 55 days post hatching (dph). During the vitelline phase, the total body length growth was scarce, whereas the muscle grew significantly, being the hypertrophy of the main mechanism involved. Both the total body length and the hypertrophy were significantly greater at 16L:8D than in the rest of photoperiod regimes. At 10 and 14 dph, the greatest body length was reached at 16L:8D, followed by the 24L group, showing the 12L:12D group the lowest values. At 14 dph, the hypertrophy and hyperplasia were also higher at 16L:8D than in the rest of groups. At 39 dph, the highest values of body length were reached in both 16L:8D and 12L:12D regimes, this latter group reaching the highest values of hypertrophy, thus showing a compensatory growth when comparing with the previous stages. The end of the metamorphosis took place at 50-55 dph in all the groups, with 2.7-3.1 cm of body length ( P > 0.05). At this stage, the transverse area of the white muscle was similar among the groups, but the greatest hypertrophy was reached at 16L:8D, whereas the highest hyperplasia was reached at 24L. [ABSTRACT FROM AUTHOR]

This study was undertaken to investigate the effects of sustained swimming exercise on the growth performance, muscle cellularity and flesh quality of juvenile qingbo fish ( Spinibarbus sinensis ). Experimental fish were exercised under four water velocities, nearly still (control, 3 cm s − 1 ) and 1, 2 and 4 body lengths (bl) s − 1 , for eight weeks at 25 °C. Then, growth performance indicated by the specific growth rate (SGR), white muscle cellularity suggested by the diameter and density of white muscle fiber, flesh quality evaluated by some textural mechanical properties (hardness, springiness, chewiness, cohesiveness) and physico-chemical parameters (pH, color, moisture, ash, protein, fat, amino acids, and fatty acids) were measured. Sustained swimming at moderate velocities (1 and 2 bl s − 1 ) resulted in a significantly higher SGR and similar white fiber diameter and density compared with the controls. However, the fish trained at a water velocity of 4 bl s − 1 displayed a similar SGR, smaller white fiber diameter and higher white fiber density compared with the controls. Sustained swimming resulted in significant increase in the values of pH and all textural traits but showed no significant effect on the color of the flesh for juvenile S. sinensis . Fish swimming under moderate water velocities exhibited higher levels of the protein content of the muscle, total essential amino acids (∑ EAA) (at 2 bl s − 1 ) and total amino acids (∑ AA) (at 1 and 2 bl s − 1 ) compared with control fish. However, the lowest levels of total amino acids (∑ AA) and total n-6 poly-unsaturated fatty acids (∑ n-6 PUFA) were observed in fish swimming at water velocity of 4 bl s − 1 . These data suggest that (1) moderate swimming exercise (1 or 2 bl s − 1 ) improved growth performance, which could not be attributed to changes in white muscle cellularity; (2) sustained swimming showed a positive effect on texture characteristics, which was partly due to the higher white fiber density and flesh pH compared with controls; and (3) moderate swimming exercise (1 or 2 bl s − 1 ) was beneficial for improving the nutritional quality of the flesh, whereas high-intensity swimming (4 bl s − 1 ) resulted in an impairment of the nutritional quality of the flesh in juvenile S. sinensis . Statement of relevance We declare that the experiments complied with the current laws of the country in which the experiments were performed and that our paper complied with the laws of commercial aquaculture. [ABSTRACT FROM AUTHOR]

Skeletal muscle growth and flesh quality were evaluated in Senegalese sole fed plant protein (PP) diets. A control fish meal-based diet (FM) was compared with three isonitrogenous (54%) and isolipidic (9%) diets with increasing levels of PP blends (50% PP50, 75% PP75 and 100% PP100). By the end of the experiment sole fed PP50 and PP75 had a body length similar to the CTR (25 cm), but fish fed PP100 were significantly smaller (23 cm). Total FM replacement (PP100) resulted in significantly smaller muscle cross sectional area mainly due to a decrease in the muscle fibre size as the total number of fibres did not vary significantly among treatments. The dietary incorporation of PP significantly reduced the expression of several key genes involved in myogenesis and muscle growth (mrf4, fgf6, myhc and mylc2). Fillet texture was affected by the total substitution of FM. Fish fed PP100 diet had a significantly higher modulus of elasticity (lower flesh stiffness) compared with the other groups. Muscle fibre size was moderately related (r = 0.573) to the modulus of elasticity and positively correlated with the expression of lysyl oxidase (r = 0.495). Muscle cellularity changes were not associated with the expression of texture-related genes (capn2, ctsb, ctsd), since no significant differences were observed among diets. The present results point towards a modulation of the expression of several muscle growth related genes by increasing levels of PP sources that alter muscle cellularity and textural properties of Senegalese sole when total FM is replaced by PP. Statement of relevance The biological basis through which sustainable and practical plant protein diets (PP) affect flesh texture determinants is extremely scarce so the present results will be valuable to the aquafeed industry, fish producers and final consumers. This study clearly shows that PP diets reduced expression of several key genes involved in myogenesis and muscle growth and can hence affect fish growth potential at long term. This study identifies useful markers that correlated well with muscle cellularity and muscle growth and can be further used to select the most appropriate diets for a fish species. [ABSTRACT FROM AUTHOR]

Hyperplasia and hypertrophy are the two mechanisms by which muscle develops and grows. We study these two mechanisms, during the early development of white muscle in Sparus aurata, by means of histology and the expression of structural and regulatory genes. A clear stage of stratified hyperplasia was identified early in the development of gilthead sea bream but ceased by 35 dph when hypertrophy took over. Mosaic recruitment of new white fibers began as soon as 60 dph. The genes mlc2a and mlc2b were expressed at various levels during the main phases of hyperplasia and hypertrophy. The genes myog and mlc2a were significantly up-regulated during the intensive stratified formation of new fibers and their expression was significantly correlated. Expression of mstn1 and igf1 increased at 35 dph, appeared to regulate the hyperplasia-to-hypertrophy transition, and may have stimulated the expression of mlc2a, mlc2b and col1a1 at the onset of mosaic hyperplasia. The up-regulation of mstn1 at transitional phases in muscle development indicates a dual regulatory role of myostatin in fish larval muscle growth. [ABSTRACT FROM AUTHOR]

We examined the effects of partial dietary supplementation with wild zooplankton or fish protein hydrolysate on cod production traits, and how they related to the expression of growth and appetite regulating transcripts and muscle cellularity. Atlantic cod larvae were fed three different diets: enriched rotifers and Artemia (RA); RA + fish protein hydrolysate (RA-PH); and RA supplemented with 5–10% wild zooplankton (RA-Zoo). Partial supplementation with zooplankton significantly improved cod dry weight at 60 days post-hatch (by approximately 4-fold), specific growth rate (by 2.5% day − 1 ) and the general development of cod larvae. Although the zooplankton fed cod were still larger at approximately 1.5 years of age, the growth advantage of this group decreased with age (the difference in wet mass decreasing from approximately 30% at 0.5 years old to 11% at 1.5 years old). In contrast, the protein hydrolysate enrichment did not improve growth, had a negative effect on survival, and increased the incidence of external deformities in 1.5 year old fish. The growth enhancement observed in the RA-Zoo larvae was largely unrelated to differences in the transcript levels of several important growth [Insulin-Like Growth Factor 1 ( igf-1 ); igf-2 ; Growth Hormone ( gh ); GH Receptor-1 ( ghr-1 ); ghr-2 ; and myostatin ( mstn )] or appetite regulating genes [Cocaine and Amphetamine Regulated Transcript ( cart) and Neuropeptide Y ( npy )], but was associated with an increase in the number and size of skeletal muscle fibers. Our findings suggest that incorporating small amounts of wild zooplankton into larval feeding regimes may significantly enhance the production of marine fishes, but that the transcript levels of the above hormones and hormone receptors are not valuable biomarkers of growth in cod larvae. Statement of relevance This research shows that small amounts of zooplankton significantly improve the growth of Atlantic cod larvae, and thus, that cultured zooplankton may be a viable and cost-effective strategy for increasing the growth (and potentially health) of intensively cultured marine finfishes. [ABSTRACT FROM AUTHOR]

A high frequency of cannibalism and high variability of growth rate within the same larval batch are the main bottlenecks for implementation of meagre culture. In this study the effect of two sodium alginate-encapsulated diets containing 55 (control) and 68% protein was tested in terms of larval composition, survival, growth and muscle cellularity. The results showed that the diet with higher protein content improved larval survival but no differences on larval growth were observed between treatments. Diets did not affect the amino acid and fatty acid profiles of meagre larvae. The differences between larval fatty acid profiles were mainly related to larval age rather than treatments. Meagre larvae fed the high protein diet showed a higher frequency of white muscle fibres with an area smaller than 150 μm 2 and a lower mean fibre area (214.9 ± 160.6 μm 2 and 187.88 ± 162.7 μm 2 , for 55 and 68% of protein, respectively). These results suggest that a higher dietary protein increases meagre larval survival and leads to a potential higher contribution of fibre hyperplasia. Statement of relevance The main aim of this work was to test two diets containing different protein levels (55 and 68%) and determine its effect on larval survival, growth, larval composition and muscle cellularity. This work was carried because meagre has been thought to have a higher protein requirement compared to seabream and seabass (Amoedo, 2011). Nevertheless, meagre is usually fed on diets formulated specifically for seabream suggesting that meagre protein requirements are not being satisfied and meagre growth might be constrained. Given that meagre is the species with highest potential to be intensively farmed in the Mediterranean region it is important to formulate specific diets for this species. The results obtained in this work showed that although growth was not affected by the diet, there seems to be a higher potential for growth in the long-term as fibre recruitment was higher when larvae were fed a high protein diet. [ABSTRACT FROM AUTHOR]

In the present study, Senegalese sole eggs incubated at 20°C were reared at three different temperatures (15°C, 18°C or 21°C) during the pelagic phase, and then transferred to a common temperature (20°C) from benthic stage until 100days post-hatch (dph). Somatic growth, fast muscle cellularity and expression of 15 growth-related genes were compared at the same developmental stage for each temperature (pre-metamorphic larvae, metamorphic larvae, post-metamorphic larvae) and at 83dph and 100dph early juveniles. During pre-metamorphosis and metamorphosis, larvae from 21°C weighed significantly more than those reared at 18°C or 15°C (P <0.001). Relative growth rate (RGR) of pelagic larvae and survival of newly-settled larvae were also higher at 21°C (P <0.05). Furthermore, an increase in muscle growth towards the highest temperatures was observed concomitantly with an increase in gene expression, namely myogenic regulatory factors (MRFs), myosins, igf-I and fgf6. After transfer to a common temperature (20°C), the 15°C group initiated a process of compensatory growth, inverting relative growth rate values that became the highest, particularly between 83dph and 100dph (P <0.05). This increased growth effort in the 15°C group was accompanied by an up-regulation of gene expression in fast muscle, particularly in the 83dph juveniles. Mrf4 and myHC were up-regulated at 15°C and positive correlations with growth were also found for myog or pax7 (P <0.05). In contrast, mstn1 was down-regulated at 15°C (P <0.05), suggesting a boost in muscle growth. By 100dph, the 15°C group had already reached the same weight as the 18°C and the same length as the 21°C ones. At this age, the 18°C juveniles had the largest mean muscle fibre diameter (P <0.001), and thus fibre hypertrophy seems to be a major growth mechanism relatively to the other groups. Our work shows that temperature during pelagic phase greatly influences the growth trajectory of Senegalese sole juveniles. [ABSTRACT FROM AUTHOR]

The 8-week rearing trial was conducted to estimate the effect of dietary hydroxyproline (Hyp) supplementation on growth performance, amino acid profiles, fatty acid profiles, and collagen concentration in muscle samples, liquid holding capacity (LHC), pH, cooking loss and antioxidant activities in flesh of post-mortem, histomorphology, ultrastructure and molecular expression of muscle samples, and raw- and cooked-fillet texture characteristics of Yellow River carp (Cyprinus carpio haematopterus). Six isoproteic and isolipidic practical diets were formulated to contain graded levels of Hyp (1.36, 3.93, 7.14, 8.86, 11.45 and 13.69 g/kg of dry matter). A total of 840 carps with an average initial weight of 17.90 ± 0.28 g were randomly allocated to 24 polypropylene tanks with funnel-shaped bottom (400 L capacity filled to 300 L and 35 fish per tank). The results showed that no significant differences were found in growth performance and morphology parameter among all treatments (P > 0.05). With the increase of dietary Hyp levels, the glycine (Gly) content, and the proportion of 22:6n-3, n-3 PUFA and collagen concentration in carp fillet showed a significant ascending tendency, while arginine and proline were in downtrend (P < 0.05). Liquid loss, lipid loss and cooking loss were significantly decreased with the increasing dietary Hyp levels (P < 0.05), and the pH values in muscle samples of carp fed with dietary Hyp (> 3.93 g/kg) were significantly higher than that in control group (P < 0.05). Dietary Hyp supplementation improved the antioxidant properties of hepatopancreas and muscle with the increasing dietary Hyp levels (P < 0.05). Overall, we posed that appropriate dietary Hyp supplementation can promote myogenesis and collagen synthesis in muscle of carp, ultimately improved the raw- and cooked-fillet texture characteristics. The current research will be contributed to find an efficient way to ensure predictable and firmer texture of farmed Yellow River carp. • Dietary Hyp promoted the synthesis of glycine and Lc-PUFA in flesh. • Dietary Hyp promoted the antioxidant properties of hepatopancreas and muscle. • Dietary Hyp improved flesh pH, LHC, cooking loss and the collagen content, and fillet texture. [ABSTRACT FROM AUTHOR]

Abstract: Fertilised eggs of Senegalese sole were incubated at 15, 18 or 21°C, and after hatching all larvae were reared at 21°C until 30days post-hatch. By this point larvae from the 18 or 21°C temperature groups had 11 and 9% more muscle fibres than those from 15°C, respectively. Hyperplastic growth during metamorphosis was higher in larvae from 18°C. Embryonic temperature induced gene expression changes, albeit with a variable pattern throughout development. Myf5, myod2, myHC and fst mRNA levels were significantly higher at several stages prior to hatching in embryos incubated at 21°C, whereas hsp90AB and hsp70 transcripts were present at higher levels in the 15°C group. Myf5, myod1, myod2, pax7, myog, fst, igf-II, igf1r, hsp90AA and hsp90AB were expressed at higher levels during early development, particularly during somitogenesis. In contrast, mrf4, myHC, mylc2, igf-I, mstn1 and hsp70 were up-regulated at later stages of larval development, namely during and after metamorphosis. This study is the first example of thermal plasticity of myogenesis with prolonged effect in a flatfish. [Copyright &y& Elsevier]

Growth performance, muscle cellularity, flesh quality, and plasma ghrelin were investigated in 0+ and 1+ farmed Atlantic salmon ( Salmo salar L.) from 40 g to 4.3 kg. Reduced meal frequency was introduced in both smolt groups from ~1.5 kg; one meal per second day (<5 °C) to one daily meal (>5 °C), while control groups were fed one to three daily meals. Results show that 0+ salmon had higher final fibre number and density, pigment content, red colour intensity, firmer flesh, and lower fillet fat content than 1+ salmon at 4.3 kg, affected by season and smolt type. Muscle fibre recruitment was an important determinant of fillet firmness and colour, possibly influenced by the prenatal temperature regime. Fish fed reduced meal frequency showed temporal reduced feeding ration, but growth performance was not compromised in any smolt groups at harvest. However, fillet fat, gaping, and colour decreased by less frequent feeding, with permanent effects in 1+ salmon for gaping and fat. Reduced meal frequency is therefore considered to be a promising tool for managing important flesh quality attributes in salmon without compromising growth performance. It is also suggested that ghrelin stimulates short-term appetite, and perhaps also in the longer term. [ABSTRACT FROM AUTHOR]

Endocrine-disrupting chemicals include natural and synthetic estrogens, such as 17α-ethynilestradiol (EE2), which can affect reproduction, growth and immunity. Estrogen signalling is mediated by nuclear or membrane estrogen receptors, such as the new G-protein-coupled estrogen receptor 1 (GPER1). The present work studies the effect of EE2 and G1 (an agonist of GPER1) on body and muscle parameters and growth-related genes of 54 two-year-old seabreams. The fish were fed a diet containing EE2 (EE2 group) and G1 (G1 group) for 45 days and then a diet without EE2 or G1 for 122 days. An untreated control group was also studied. At 45 days, the shortest body length was observed in the G1 group, while 79 and 122 days after the cessation of treatments, the shortest body growth was observed in the EE2 group. Hypertrophy of white fibers was higher in the EE2 and G1 groups than it was in the control group, whereas the opposite was the case with respect to hyperplasia. Textural hardness showed a negative correlation with the size of white fibers. At the end of the experiment, all fish analyzed in the EE2 group showed a predominance of the gonadal ovarian area. In addition, the highest expression of the mafbx gene (upregulated in catabolic signals) and mstn2 (myogenesis negative regulator) was found in EE2-exposed fish. [ABSTRACT FROM AUTHOR]

Larval muscle development in Atlantic salmon is known to be affected by temperature; however, the long term effects and possible mechanisms involved are less well understood. Therefore, the aim of this study was to evaluate the influence of egg incubation temperature on post-hatch muscle growth and fish activity. Salmon eggs were incubated at either 10°C or 5°C from fertilization until hatching, then subsequently both groups were reared at 5°C. Fish from both groups were sampled at the eyed stage, 6 and 21 weeks after first feeding, for muscle cellularity analysis and immunocytochemistry. In addition, to try to establish a mechanism for altered growth, the activity of the fish was measured at 3, 6 and 21 weeks after first feeding. Our results demonstrate that whereas fish incubated at 10°C grow faster, the fish incubated at 5°C show a more sustained period of muscle growth and by 21 weeks are significantly longer, heavier and have more muscle fibres than those fish incubated at a higher temperature. We also demonstrate that fish raised at 5°C show increased food seeking activity throughout development and that this may explain their sustained growth and muscle development. These results taken together, demonstrate that egg incubation temperature up to hatching in salmon is critical for longer term muscle growth, twinned with increased activity. This is of interest to the aquaculture industry in term of the production of good quality fish protein. [ABSTRACT FROM AUTHOR]

Abstract: Muscle characteristics that are important for flesh quality traits were assessed in populations of wild and farmed Atlantic salmon (Salmo salar L.). The wild fish were obtained from a commercial fishery on the North Esk, Scotland in 2001 and 2003. The farmed fish comprised 7families from the Stofnfiskur breeding programme (Stofnfiskur A/S, Iceland) grown in 5m×5m×5m net pen sea cages in a dedicated trial unit on South Uist, Scotland. Total carotenoid pigment (mgkg−1 wet mass flesh) concentrations were higher in farmed (7.68 and 8.43 for grilse and salmon, respectively) than wild fish (5.53 and 6.44 for grilse and salmon, respectively). In contrast, the average flesh colour, measured with a SalmonFan™, was similar for all groups (27.4 to 28.0), indicating a superior colour visualisation per unit pigment concentration in wild fish. The flesh lipid content was 46%-higher (grilse) and 84%-higher (salmon) in farmed than wild fish. Vitamin E concentrations per unit wet mass lipid were similar in wild and farmed salmon and in the range (208–259mgkg−1). Fillet firmness was measured using a shear test and instrumental texture analyser. The work done (WD) to shear standardised post-rigor muscle samples was higher in grilse than salmon and was significantly greater for the wild (710 and 811mJ, respectively) than farmed (415 and 602mJ, respectively) fish, indicating a firmer texture in the wild fish. The grilse and salmon sampled had stopped recruiting fast muscle fibres and both wild and farmed fish had around 650,000fibres per trunk cross-section. Thus differences in fillet texture and colour between these populations could not be explained by the muscle cellularity which was similar between groups. Hydroxyproline (HYP) was used to estimate collagen concentration. Alkaline-insoluble HYP was 72.5% higher in wild than farmed salmon (14.0 vs. 8.1μmolg−1 dry mass, respectively) whereas alkaline-soluble HYP was 5.2-fold higher in farmed than wild salmon (31.0 vs. 6.0μmolg−1 dry mass, respectively). The alkaline-insoluble collagen fraction is thought to be enriched with reducible and non-reducible cross-linked collagen. There was a significant positive correlation between pyridinoline (PYD) crosslink concentration and WD, explaining 25% of the within population variation in firmness. However, PYD concentration (pmolg−1 dry mass) was similar between wild (476) and farmed (445) salmon and cannot explain the differences in flesh firmness observed between populations. It was hypothesised that the higher average values of firmness in the wild than farmed salmon flesh can in part be attributed to higher concentrations of reducible immature collagen crosslinks. [Copyright &y& Elsevier]