Greater amberjack (Seriola dumerili) is a very promising candidate for the diversification of aquaculture, yet high growth dispersion at hatchery stages and unsynchronized development is a major drawback in intensifying juvenile production. 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.
Rotifers (R) and copepods (C) were the live feed alternatives studied in a 2X2 rearing experiment combined with two different rearing temperatures (20 oC vs 24 oC). Larvae samples were collected at notochord flexion (FL), end of larva rearing (ELR) and middle metamorphosis (MM) and the total cross-sectional area (TCSA) of white muscle was measured along with the expression of mylpfa (myosin light chain 2a, hypertrophy), mylpfb (myosin light chain 2b, hyperplasia), myog (myogenin, coordination of myogenesis).
Total length increase was almost linear after hatching and the combined effect of temperature X live feed significantly affected larval growth (p=0.037), whereas TCSA was strongly affected by the type of live feed (p= 0.039). The expression levels of mylpfa gene were affected neither from the temperature nor from the type of live feed. Significant differences were identified in the expression of mylpfb and myog genes between the four groups; at FL, expression of myog that drives muscle cell differentiation and of mylpfb that signifies hyperplasia, was higher in larvae reared at 24oC. By ELR, group 24R exhibited the highest myog and mylpfb expression. 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 the mylpfa/mylpfb expression levels, it appears that hyperplasia dominates the white muscle development up to metamorphosis and it is strongly affected by rearing temperature.
The combined results from histological and gene expression analyses indicate that temperature is a major driver of white muscle development, with 24oC favoring a higher pace in comparison with 20oC. Within 24oC, the type of live feed resulted in different phenotypes at MM with rotifers supporting longer larvae with smaller TCSA as compared with copepods.
Acknowledgement: 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.