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Somatic growth is a balance between protein synthesis and degradation, and it is largely influenced by nutritional clues. Antioxidants levels play a key role in protein turnover by reducing the oxidative damage in the skeletal muscle, and hence promoting growth performance in the long-term. In the present study, Senegalese sole postlarvae (45 days after hatching, DAH) were fed with three experimental diets, a control (CTRL) and two supplemented with natural antioxidants: curcumin (CC) and grape seed (GS). Trial spanned for 25 days and growth performance, muscle cellularity and the expression of muscle growth related genes were assessed at the end of the experiment (70 DAH). The diets CC and GS significantly improved growth performance of fish compared to the CTRL diet. This enhanced growth was associated with larger muscle cross sectional area, with fish fed CC being significantly different from those fed the CTRL. Sole fed the CC diet had the highest number of muscle fibers, indicating that this diet promoted muscle hyperplastic growth. Although the mean fiber diameter did not differ significantly amongst treatments, the proportion of large-sized fibers (>25 μm) was also higher in fish fed the CC diet suggesting increased hypertrophic growth. Such differences in the phenotype were associated with a significant up-regulation of the myogenic differentiation 2 (myod2) and the myomaker (mymk) transcripts involved in myocyte differentiation and fusion, respectively, during larval development. The inclusion of grape seed extract (GS diet) resulted in a significant increase in the expression of myostatin1. These results demonstrate that both diets (CC and GS) can positively modulate muscle development and promote growth in sole postlarvae. This effect is more prominent in CC fed fish, where increased hyperplastic and hypertrophic growth of the muscle was associated with an upregulation of myod2 and mymk genes. [ABSTRACT FROM AUTHOR]

Abstract In the present work, recent studies that contributed for improving dietary protein in practical microdiets for Senegalese sole larvae are revised, in an attempt to overcome some of the current problems in this species larviculture, such as the difficult early adaptation to inert diets and highly variable growth rates. Different diet formulation strategies were employed in an attempt to improve Senegalese sole larvae capacity to utilize and deposit protein throughout metamorphosis, to further maximize growth potential: (1) increasing indispensable amino acids (IAA) content; (2) meeting the ideal IAA profile by adjusting the dietary AA profile to the larval body AA profile; and (3) decreasing the complexity (molecular weight) of dietary protein to increase its digestibility. Either manipulating the quality or the complexity of dietary protein had impact on the larvae capacity to utilize protein and direct it for growth. Sole larvae seem to be able to adapt their digestive functions and metabolic capacity to dietary protein. Moreover, increasing the dietary IAA/DAA ratio and changing the degree of hydrolysis of dietary protein affected the expression pattern of muscle growth related genes, with consequences on muscle cellularity and potential for growth. The expression of DNA methyltransferases was altered in response to changes in dietary protein. The novelty of such information in fish may trigger further studies on the effect of dietary protein on the epigenetic regulation of growth. In conclusion, optimal protein quality for Senegalese sole seems to change during larval development. Whereas the inclusion of a moderately hydrolysed protein comes up as a promising way to improve growth in early larval stages, larger peptides and intact protein seem to be more suitable to sole post-larvae and young juveniles. Therefore, these results suggest that dietary protein fraction formulation of microdiets for Senegalese sole should be adapted to each developmental stage, what has important consequences for practical larval microdiets formulation and feeding protocols. Highlights • Manipulating dietary protein quality or complexity had different effects on sole larvae capacity to utilize and retain protein. • Changing dietary IAA/DAA ratio or protein complexity affected myogenesis, which reflected on sole somatic growth potential. • More than dietary AA profile, changing dietary protein complexity shows as a promising way to improve growth in sole early larvae. • Dietary protein formulation of microdiets for Senegalese sole should be adapted to each developmental stage. [ABSTRACT FROM AUTHOR]

Feeding is a complex process including food uptake, digestion and processing of the absorbed nutrients, therefore it is required to cover the postprandial period to obtain a global and integrated view of the digestive function. As in the case of fish larvae where the animals may eat ad libitum , it is more adequate to study the feeding and digestion patterns on a daily basis. The aim of the present work was to present an overview on the digestive process throughout the daily cycle in Senegalese sole larvae and post-larvae. The work has included the assessment of feeding and digestion patterns, as well as the regulation of the digestive processes, with the global objective to improve the knowledge of the physiological basis underlying the digestive function and, as consequence, to improve feeding efficiency. [ABSTRACT FROM AUTHOR]

Due to its high protein synthesis and deposition rates, skeletal muscle protein deposition is a major determinant of fish growth. Dietary protein complexity is likely to influence protein utilization and deposition in skeletal muscle, possibly affecting fish myogenesis. In this study, three microdiets were formulated with different degree of hydrolysis of dietary protein as the changing factor: one diet contained a mix of intact protein sources targeting a peptide with molecular weight >20 kDa (Intact); a second diet contained a hydrolysate with polypeptides ranging from 5 to 70 kDa (PartH); and a third diet contained a high level of a protein hydrolysate mostly composed of small peptides (<5 kDa) (HighH). A possible effect on the regulation of muscle growth in Senegalese sole larvae was evaluated through white muscle cellularity and the expression of muscle growth-related genes at 16 and 36 DAH. The PartH diet promoted white muscle growth during the metamorphosis climax (16 DAH), which was reflected on increased body weight. At 36 DAH, different diets induced different expression patterns of genes encoding for the myogenic regulatory factors, which affected muscle growth dynamics, ultimately promoting growth potential in the Intact group. A lower recruitment of small-sized fibres in the PartH and HighH groups led to reduced potential for muscle growth, which resulted on further reduced somatic growth. Accordingly, fish fed the Intact diet grew better up to a late juvenile stage (60 DAH) and were still heavier than others even after 30 days of feeding all groups on the same commercial diet, at 90 DAH. The up-regulation in the transcript levels of genes encoding for de novo DNA methyltransferases in the HighH group suggest a potential for nutritional programming in this species. [ABSTRACT FROM AUTHOR]

The full expression of growth potential in fish larvae largely depends on an efficient protein utilization, which requires that all the indispensable amino acids (IAAs) are provided at an optimum ratio. The effect of supplementing a practical microdiet with encapsulated crystalline-AA to correct possible IAA deficiencies was evaluated in Senegalese sole larvae. Two isonitrogenous and isoenergetic microdiets were formulated and processed to have approximately the same ingredients and proximate composition. The control diet (CTRL) was based on protein sources commonly used in the aquafeed industry. In the supplemented diet (SUP) 8% of an encapsulated fish protein hydrolysate was replaced by crystalline-AA in order to increase the dietary IAA levels. The microdiets were delivered from mouth-opening upon a co-feeding regime until 51 days after hatching (DAH). The larvae capacity to utilize protein was evaluated using an in vivo method of controlled tube-feeding during relevant stages throughout development: pre-metamorphosis (13 DAH); metamorphosis climax (19 DAH) and metamorphosis completion (25 DAH). Somatic growth was monitored during the whole trial. A possible effect on the regulation of muscle growth was evaluated through muscle cellularity and the expression of related genes ( myf5 , myod2 , myogenin , mrf4 , myhc and mstn1 ) at metamorphosis climax (19 DAH) and at a juvenile stage (51 DAH). The SUP diet had a negative impact on larvae somatic growth after the metamorphosis, even though it had no effect on the development of Senegalese sole larvae capacity to retain protein. Instead, changes in somatic growth may reflect alterations on muscle growth regulation, since muscle cellularity suggested delayed muscle development in the SUP group at 51 DAH. Transcript levels of key genes regulating myogenesis changed between groups, during the metamorphosis climax and at the 51 DAH. The group fed the SUP diet had lower dnmt3b mRNA levels compared to the CTRL group. Further studies are needed to ascertain whether this would possibly lead to an overall DNA hypomethylation in skeletal muscle. Statement of relevance In farmed fish species, there has been a great effort over the years to provide the best conditions for successful development of embryos and small larvae, as early environmental conditions can strongly affect muscle growth during early stages and influence the subsequent growth potential at later life stages. In spite of increased efforts to understand the regulation of myogenesis by intrinsic factors like genotype and extrinsic factors such as photoperiod and temperature, studies evaluating the impact of nutritional factors on fish larvae muscle development are still very scarce. This work will raise interest to the discussion on whether a nutritional cue during an early developmental stage can impact on the regulation of muscle growth and on further growth potential in a metamorphosing farmed fish species, such as Senegalese sole. Supplementing microdiets with crystalline-AA in order to correct dietary IAA did not improve Senegalese sole larvae somatic growth and led to changes on the regulation of muscle growth associated with changes in expression patterns of muscle growth markers during the trial (secondary MRFs myogenin and mrf4 , myhc and mstn1 ). Dietary IAA affected the expression of a DNA methyltransferase essential for de novo methylation, dnmt3b , suggesting that an epigenetic effect at the transcriptional regulation level may explain differences found in somatic growth as a response to a nutritional cue. This work may contribute to lay down basis for future studies on nutritional programming of muscle growth in fish larvae of important farmed species. [ABSTRACT FROM AUTHOR]

The Senegalese sole is a marine pleuronectiform that naturally occurs in Southern Europe and Mediterranean region where it is being produced in aquaculture, in particular in Portugal and Spain. The aim of this study was to assess the quality of hatchery-reared larvae in comparison with those reared in the wild, and determine to which extension wild growing larvae are also affected by skeletal deformities. The main structures affected included those forming the axial skeleton, the caudal fin complex and both anal and dorsal fins, with the most prevalent anomalies affecting caudal vertebrae and arches. Hatchery-reared fish presented a higher incidence of deformities (79%) compared with the 19% observed in wild specimens. In wild postlarvae collected in Autumn no deformities were observed. This work clearly shows that wild Senegalese sole present less skeletal deformities than those hatchery-reared during larval stages, indicating a selective mortality of wild deformed fish and/or an effect of aquaculture-related rearing conditions in the development of skeletal deformities in sole. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to determine if sole larvae co-fed with inert diet at mouth opening would perform better than larvae fed with live prey and if such a feeding regime would produce better quality juveniles. The experiment was separated in to two phases: pelagic and benthic. In the pelagic phase, treatments consisted of the standard feeding regime (rotifer and Artemia feeding), the standard feeding regime and inert diet, and rotifer for a longer period than the standard feeding regime until larvae reached 9 days after hatching (DAH). By the end of the pelagic phase, when the postlarvae were 20 DAH, sole that were co-fed with inert diet from mouth opening, were significantly smaller in weight than postlarvae fed exclusively with live prey. Sole digestive maturation was improved by co-feeding the inert diet. Survival rates, skeletal deformities and quality evaluation were not affected by the feeding regimes. In the benthic phase, the postlarvae from standard feeding regime (pelagic phase) were separated in to two treatments: standard live Artemia metanauplii until weaning and standard frozen Artemia metanauplii until weaning. Remaining treatments were the follow up of treatments from the pelagic phase. At the end of the experiment i.e. 68 DAH, the postlarvae co-fed with inert diet from mouth opening were significantly larger than all the postlarvae from remaining feeding regimes. The results of the present study demonstrate that it is possible to offer inert diet to sole at mouth opening in a co-feeding regime and to produce better quality postlarvae. Co-fed sole were larger and had a better tail condition at the end of the weaning. [Copyright &y& Elsevier]

To optimize Senegalese sole-weaning strategies, three experiments were performed. The first trial tested four weaning strategies with a 10 mg sole. Artemia-fed sole grew threefold less than fish fed an inert diet. Sudden weaning (abrupt change from Artemia to inert diet) and weaning with co-feeding produced larger sole than did a late weaning treatment; delayed weaning negatively affected fish growth. In the second experiment, the digestive capacity of early-weaned 1, 2 and 4 mg sole was investigated. The highest growth was observed in sole weaned at 4 mg. Digestive enzyme profiles suggest that sole have an adaptation period to inert diets, with reduced feed intake. This adaptation period is inversely proportional to post-larvae weight. The third experiment examined weaning with co-feeding at different weights (2, 5 and 11 mg). These studies demonstrate that sole of 5–10 mg can be weaned, with high survival rates. On the basis of the digestive enzyme profiles, the early introduction of inert diets in co-feeding with Artemia seems to affect intestinal processes in smaller postlarvae. This study also suggests that trypsin and alkaline phosphatase may be used as indicators of nutritional status in sole of <5 mg. [ABSTRACT FROM AUTHOR]

Simple Summary: Oxidative stress has a direct impact on the welfare of fish, affecting growth performance and health status. Natural plant extracts present a high antioxidant capacity, due to a diversity and abundant content of polyphenols. Thus, the aim of this work was to identify if plant extracts, such as curcumin, green tea, and grape seeds, can promote oxidative status, and ultimately, enhance the growth and physiological stress response of postlarvae. Our results showed that plant extracts can improve the growth and oxidative status of the fish. Moreover, they may help fish to cope under stressful conditions. Dietary formulations with natural supplements may be a viable strategy to improve fish robustness during early life stages, and can therefore contribute to the development of aquafeeds and promote the sustainability of aquaculture production. Plant extracts are known for their high content and diversity of polyphenols, which can improve fish oxidative status. A growth trial with Senegalese sole postlarvae (45 days after hatching) fed with one of four experimental diets—control (CTRL), and supplemented with curcumin (CC), green tea (GT), and grape seed (GS) extracts—was performed to assess if supplementation could improve growth performance and oxidative status. At the end of the growth trial, postlarvae were submitted to a thermal stress to assess their robustness. Sole growth was improved by CC and GS diets when compared to those fed the CTRL. CC and CTRL postlarvae presented the lowest oxidative damage (lipid peroxidation and protein carbonylation values). Stress-related biomarkers (heat shock protein 70 and glutathione-S-transferase) decreased in CC fish compared to those fed the CTRL diet, which might be due to a direct antioxidant capacity. In contrast, oxidative damage increased in GT and GS sole reared in standard conditions. However, after a thermal stress, GT and GS diets prevented the increase of protein carbonylation content and the decrease of antioxidant glutathione, depending on exposure time. Overall, dietary supplementation with natural extracts modulated oxidative status and stress response after a short/long-term exposure to temperature. [ABSTRACT FROM AUTHOR]

Senegalese sole ( Solea senegalensis ) is a highly valuable flatfish species targeted for aquaculture diversification in Southern-European countries. Although its adaptation to captivity was foreseen in the 1970´s, its commercial production at a relevant industrial scale is extremely recent. One of the factors causing this delay in commercialisation was a severe bottleneck occurring during weaning, where incipient larval growth performances and survivals were impairing farming during the first decades of farming. However, a significant evolution has recently occurred for Senegalese sole weaning, with larval growth rates, survivals and quality drastically increasing, and good results becoming more reproducible. These progresses were only possible following significant R&D efforts leading to increased knowledge on larval nutritional physiology, weaning strategies, feeding practices and microdiet formulation and production. To this end, this work reviews the advancements that contributed for the evolution occurring in Senegalese sole weaning during the last decades. This overview shows that, for instance, while in the year 2000 larval weaning would only be achieved at around 60 days after hatching (DAH), with fish achieving 1 g (wet weight basis) at around 120 DAH, nowadays it is possible to perform an early weaning starting immediately after settling (15 DAH) and achieving 1 g at 65 DAH. Future perspectives on Senegalese sole weaning should target an optimisation of microdiet nutritional and physical properties to a further adequacy for the pelagic larvae, where the predatory capacity is reduced and lower particle sizes lead to fast and high nutrient leaching. Nevertheless, this work shows that early life-feed replacement is a reality for Senegalese sole, although it remains uncertain if it will ever occur at the onset of exogenous feeding. [ABSTRACT FROM AUTHOR]