Early temperature effects on muscle growth dynamics and histochemical profile of muscle fibres of sea bass Dicentrarchus labrax L., during larval and juvenile stages

Recently, it has been found that the thermal experience during the earliest phases of development could determine the larval and postlarval growth characteristics of teleosts. In order to investigate the effects of the early temperature regime on the advanced stages of growth of sea bass, Dicentrarchus labrax L., this species was reared during the vitelline phase at two temperatures: natural temperature (15 °C) and 17.7±0.1 °C, and then larvae transferred to common temperature (natural temperature). Muscle growth was studied by morphometric and histochemical techniques (mATPase and NADH-TR). Body length and body mass were also measured. During the vitelline phase, muscle growth was similar in both experimental groups, but at 25 days, both hypertrophy and hyperplasia of white muscle fibres were greater in the prewarmed group (p<0.05). At the end of metamorphosis (80 days) and at 120 days, the average diameter of white muscle fibres, as well as the body length, were greater in the prewarmed group (p<0.05), but the number of white fibres did not differ significantly between groups. The morphological mosaic of white muscle fibres was observed at the end of metamorphosis, and the histochemical mosaic appeared gradually since the early postlarval stages. Thus, at 120 days, some specimens in both experimental groups showed three or four different mATPase staining white fibres: low (L), moderate (M), high (H) and/or very high (vH), whereas in other specimens, only L or M mATPase activity fibres were observed. Early T influenced the histochemical maturity of the white muscle. By 120 days, the proportion of H and vH fibres was greater in the prewarmed group (p=0.027; p=0.051, respectively). By 154 days, the four mATPase staining profiles (L, M, H, vH) were observed in all specimens of both groups, but the proportion of vH fibres was still higher in the prewarmed group. By 188 days, 3774 °C-day for the prewarmed group and 3759 °C-day for the natural temperature group, only slight differences between groups were observed in the histochemical properties and no differences were found in the number and size of white muscle fibres, neither in the body length and body mass of specimens.

In conclusion, a slight increase of temperature during the vitelline phase of sea bass increased the muscle growth and body length of fish in subsequent larval and postlarval stages, and advanced the histochemical maturity of the white muscle.