Insights into the early gonad development of the protogynous ballan wrasse (Labrus bergylta)

The reproductive biology of ballan wrasse, a popular cleaner fish species now bred in captivity, is not well understood particularly the early stages of development and their accompanying endocrine changes. The protogynous nature of this species has been well documented in the wild, although it is still unclear if it follows a monandric or diandric hermaphroditism. In this study, we investigated the gonad development of hatchery produced ballan wrasse (n = 102) between 3 and 185 g body weight and 5-19 cm total length. About 90 % of all fish examined showed gonads undergoing primary oocyte growth, exhibiting chromatin-nucleolar stage, perinucleolar stage, and early cortical alveolar stage. Mean size of fish that entered primary oocyte growth (i.e., chromatin-nucleolar stage) is 26.2 +/- 1.6 g and 10.9 +/- 0.2 cm. The remaining 10 % were undifferentiated and constituted the smallest fish examined. The gonadosomatic index and circulating levels of 17 beta-Estradiol and Testosterone increased as fish progressed through the ovarian development. Expression levels of selected gonadal genes including cyp19a1a, figla, bmp15, dmrt1, amh, fshr, and lhr were also quantified. To the best of our knowledge, this paper is the first to investigate the early reproductive development of ballan wrasse, providing important insights into histological and endocrine changes. Results from this study provide basis for further research on the reproductive physiology of ballan wrasse as well as for the development of broodstock management techniques in this economically important cleaner fish.