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Relative expression of myogenic regulatory factors in fast muscle of Atlantic cod and the influence of photoperiod manipulation in their expression plasticity

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Kjetil Aune

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kjetil.aune@nofima.no

Genomics in Aquaculture 2011; Crete, 2011-09-14–2011-09-17

Nagasawa, Kazue; Lazado, Carlo C.; Fernandes, Jorge

Fish that have a clear reproductive season lose enormous amount of energy with sexual maturation prior to spawning. In aquaculture condition, it has been reported for several species that early puberty results in weight loss and flesh quality in farmed fish. Photoperiod manipulation is one of the most typical and effective treatments for delaying Atlantic cod (Gadus morhua L.) maturation not only laboratory scale, but also industrial scale. In particular, this treatment might have a possibility to enhance growth in this species, since it has recently demonstrated that a short period continuous light treatment promotes significant body gain in cod juveniles. However, the molecular mechanism underlying this enhanced body gain induced by photic signals is still unclear. Myogenic regulatory factors (MRFs) are a group of transcription factors that play a key role in myogenesis. The possible correlation between MRFs expression and photoperiod manipulation in cod is yet to be investigated. In the present study, we evaluated the impact of photoperiod manipulation for 6 months in Atlantic cod juveniles both in terms of growth and mRNA expression levels of MRFs (myoD and myoG) in fast muscle during photoperiod treatment by quantitative-PCR (qPCR) analyses. To compare mRNA expression levels of above genes in fast muscle between two groups reared under different photoperiod conditions, one fish group was kept under continuous illumination whereas the other was kept under a light regime that corresponded to natural photoperiod conditions in Bodø (Norway) from January to July 2010. Interestingly, during the 6 months of photoperiod treatment, significant differences in mean weight were observed at 120 and 180 days. The mean weight for the continuous light group was 15% and 10% higher than the normal light condition group at 120 and 180 days, respectively. However, qPCR analyses revealed no significant difference in myoD and myoG expression in fast muscle of fish from both groups. Expression of myf-5 and MRF4 will also be examined in order to reveal if they could trigger the significant body gain that is obtained by photoperiod manipulation.