The Effect of Continuous Light on Growth and Muscle-Specific Gene Expression in Atlantic Salmon ( L.) Yearlings.

Photoperiod is associated to phenotypic plasticity of somatic growth in several teleost species, however, the molecular mechanisms underlying this phenomenon are currently unknown. The effect of a continuous lighting (LD 24:0), compared with the usual hatchery lighting (HL) regime, on the growth rate and gene expression of myogenic regulatory factors (MRFs: paralogs, , and ) myosin heavy chain (), and paralogs in the white muscles of hatchery-reared Atlantic salmon yearlings was evaluated over a 6-month period (May to October). The levels of gene expression were determined using real-time PCR. Continuous lighting was shown to have a positive effect on weight gain. , , , and mRNA expression was influenced by the light regime applied. In all the studied groups, a significant positive correlation was observed between the expression levels of MRFs and paralogs throughout the experiment. The study demonstrated seasonal patterns regarding the simultaneous expression of several MRFs. , , and mRNA expression levels were elevated in the mid-October, but , and mRNA levels decreased by the end of this month. In general, the findings showed that constant lighting affected the regulatory mechanisms of muscle growth processes in salmon.