Larval dietary protein complexity affects the regulation of muscle growth and the expression of DNA methyltransferases in Senegalese sole

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.