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- What determines growth potential and juvenile quality of farmed fish species?Publication . Valente, L. M. P.; Moutou, K. A.; Conceição, L. E. C.; Engrola, S.; Fernandes, J. M. O.; Johnston, Ian A.Enhanced production of high quality and healthy fry is a key target for a successful and competitive expansion of the aquaculture industry. Although large quantities of fish larvae are produced, survival rates are often low or highly variable and growth potential is in most cases not fully exploited, indicating significant gaps in our knowledge concerning optimal nutritional and culture conditions. Understanding the mechanisms that control early development and muscle growth are critical for the identification of time windows in development that introduce growth variation, and improve the viability and quality of juveniles. This literature review of the current state of knowledge aims to provide a framework for a better understanding of fish skeletal muscle ontogeny, and its impact on larval and juvenile quality as broadly defined. It focuses on fundamental biological knowledge relevant to larval phenotype and quality and, in particular, on the factors affecting the development of skeletal muscle. It also discusses the available methodologies to assess growth and larvae/juvenile quality, identifies gaps in knowledge and suggests future research directions. The focus is primarily on the major farmed non-salmonid fish species in Europe that include gilthead sea bream, European sea bass, turbot, Atlantic cod, Senegalese sole and Atlantic halibut.
- Incubation temperature induces changes in muscle cellularity and gene expression in Senegalese sole (Solea senegalensis)Publication . Campos, C.; Valente, L. M. P.; Conceição, L. E. C.; Engrola, S.; Sousa, V.; Rocha, E.; Fernandes, J. M. O.Fertilised eggs of Senegalese sole were incubated at 15, 18 or 21 °C, and after hatching all larvae were reared at 21 °C until 30 days 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.
- Temperature affects methylation of the myogenin putative promoter, its expression and muscle cellularity in Senegalese sole larvaePublication . Campos, C.; Valente, L. M. P.; Conceição, L. E. C.; Engrola, S.; Fernandes, J. M. O.Myogenin (myog) encodes a highly conserved myogenic regulatory factor that is involved in terminal muscle differentiation. It has been shown in mammals that methylation of cytosines within the myog promoter plays a major role in regulating its transcription. In the present study, the Senegalese sole (Solea senegalensis) myog putative proximal promoter was identified and found to be highly conserved among teleosts. Therefore, it is plausible that it plays a similar role in controlling myog expression. Cytosine methylation of the myog promoter in skeletal muscle of Senegalese sole larvae undergoing metamorphosis was influenced by rearing temperature. A lower temperature (15°C) significantly increased myog promoter methylation in skeletal muscle, particularly at specific CpG sites, relatively to higher rearing temperatures (18 and 21°C). Myog transcription was downregulated at 15°C, whereas expression of dnmt1 and dnmt3b was upregulated, consistently with the higher myog methylation observed at this temperature. Rearing temperature also affected growth and fast muscle cellularity, producing larger fibers at 21°C. Taken together, our data provide the first evidence of an epigenetic mechanism that may be underlying the temperature-induced phenotypic plasticity of muscle growth in teleosts.
- Thermal conditions during larval pelagic phase influence subsequent somatic growth of Senegalese sole by modulating gene expression and muscle growth dynamicsPublication . Campos, C.; Fernandes, J. M. O.; Conceição, L. E. C.; Engrola, S.; Sousa, V.; Valente, L. M. P.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 100 days 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 83 dph and 100 dph 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 83 dph and 100 dph (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 83 dph 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 100 dph, 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.