Greater amberjack (Seriola dumerili) is a very promising candidate for the diversification of the Mediterranean aquaculture due to high growth rates, consumer appreciation and commercial value. However, high growth dispersion at hatchery stages and unsynchronized development is a major drawback in intensifying juvenile production. Temperature is a key factor in promoting fish development and growth with strong epigenetic effects. Feeding at early stages is another challenging factor given the lack of a fully functioning digestive system. In this study, we investigated the influence of different rearing temperatures and different live feeds, on the process and variation of myogenesis at early development in greater amberjack.
Greater amberjack eggs were subjected to a 2X2 rearing experiment; two different rearing temperatures (20 oC vs 24 oC) were combined with two different types of live feeds [copepods (C) vs rotifers (R)] to form four experimental groups (20C, 20R, 24C, 24R). Larvae samples were collected at three developmental stages; notochord flexion (FL), end of larva rearing (ELR) and middle metamorphosis (MM). Larvae were subjected to histological analysis and the total cross-sectional area (TCSA) of one epaxial quadrant of white muscle was measured. In addition, the expression of mylpfa (myosin light chain 2a, hypertrophy), mylpfb (myosin light chain 2b, hyperplasia), myog (myogenin, coordination of myogenesis) that mark crucial mechanisms of muscle development and growth, was quantified by real-time PCR.
The combined results from histological and gene expression analyses indicate that temperature is a major factor with 24oC favoring a higher pace of white muscle development in comparison with 20oC. Within 24oC, the type of live feed used resulted in different phenotypes at MM with rotifers supporting longer larvae with smaller TCSA as compared with copepods. A higher development pace was accompanied by a higher variation in gene expression levels that were not accompanied by higher variation in phenotypic traits, i.e. TL and TCSA. The shift from larvae to juveniles is dependent on the proper deployment of hyperplastic and hypertrophic processes during the early phases of muscle development. Based on mylpfa/mylpfb expression levels, it appears that hyperplasia dominates the white muscle development up to metamorphosis and it is strongly affected by rearing temperature.
«This research was Co-financed by Greece and the European Union, European Maritime and Fisheries Fund in the context of the implementation of the Greek Operational Programme for Fisheries, Priority Axis “Innovation in Aquaculture”, Project title " Investigation of size variability in reared juveniles of greater amberjack towards improved production and husbandry practices" MIS 5010923.