Oocyte development and ovarian maturation of the black triggerfish, Melichthys niger(Actinopterygii: Balistidae) in São Pedro e São Paulo Archipelago, Brazil

The oogenesis is a key stage in the reproductive development of an organism, which can be best understood from histological analysis of ovaries in different maturity stages. In order to provide information on the reproductive biology of the black triggerfish, M. niger, in particular on its oogenesis process, this study aimed at identifying and characterizing the oocyte development stages and its organization within the different stages of ovarian maturation based on specimens from São Pedro e São Paulo Archipelago. In this present report, a number of 294 ovaries were histologically analyzed. It was verified that they are composed of ovigerous lamellae containing oocytes at different development stages. Five different stages of oogenesis were identified: young cells, with an average size of 12.9 ìm; previtellogenic oocytes (perinucleolar), with an average size of 53.5 ìm; cortical-alveoli oocytes with an average size of 83.1 ìm; vitellogenic oocytes, with an average size of 160.4 ìm and mature oocytes, with an average size of 289.8 ìm. In addition to the germ cells, some somatic structures were also identified, such as: ovarian wall, follicular cells and blood vessels. Based on the type and number of oocytes observed, four stages of ovarian maturation were identified: early maturation, represented by only 2.2% of the sample; middle maturation, represented by 9.9%; mature, represented by 44.2% and resting, represented by 43.9%. The identification of five oocyte development stages in the ovarians from M. niger, suggested that the specie follows a pattern similar to that described for other marine fish