Incidence of early onset puberty in two-year-old female sea bass, Dicentrarchus labrax L.

The incidence of early onset puberty in female aquaculture fish species is less well known than in males and, it merits to be taken into account in order to properly address its outcomes. The goal of this study was to compare the growth performance and reproductive physiology between 2-year-old female sea bass with early or late onset puberty. Fish from seven fertilized egg cohorts of sea bass were considered. Animals were individually tagged and histologically identified when terminally sampled over the first and second year of life. Ovaries from 1-year -old females were in the chromatin nucleolus (CN) or perinucleolar stage (PN), whereas 2-year-old females showed oocytes in the PN stage and early vitellogenesis (EV) (GSI < 0.7%) or late vitellogenesis (LV) (GSI of 4.45 +/- 0.55%). Accordingly, 2-year-old females with less advanced reproductive development were considered as fish with late onset puberty (PN, EV), in contrast to their counterparts that were considered to be fish with early onset puberty (LV). Non-spawning females with early onset puberty were observed. The early onset puberty occurred in 18.1 +/- 6.4% of fish in the population, although it was variable among the cohorts. Body size of early pubertal females was usually larger than that of fish with late onset puberty (28.7% heavier in weight and 7.9% greater in fork length). Differences in circulating levels of the insulin-like growth factor-1 (Igf-1) and those of 17-beta estradiol (E2), follicle-stimulating hormone (Fsh) and vitellogenin (Vtg) one year before spawning, significantly contributed to explaining the total variance associated with the early onset puberty in this species. This study provides valuable information on the interplay that these factors might have at the onset of early puberty in fish and, in turn, its potential use as key indicators of this trait in the female sea bass.