Caracterização morfológica das gônadas e desenvolvimento ovariano da cavala Acanthocybium solandri (Cuvier, 1832) (Perciformes: Scombridae) e do dourado Coryphaena hippurus (Linnaeus, 1758) (Perciformes: Coryphaenidae) no Arquipélago de São Pedro e São Paulo, Brasil

Abstract

More accurate studies and evaluations of the reproductive parameters of species, especially oocyte development, are fundamental to better understand the life history of the species, since this information is essential for the adoption of an efficient fisheries management. The objective of this study was to describe the dynamics of the oogenesis process through the evaluation of aspects related to the reproductive biology of mackerel (Acanthocybium solandri) and dorado (Coryphaena hippurus), caught in the Archipelago of São Pedro and São Paulo, Brazil. For the analysis, 276 gonads of mackerel and 132 of gilthead sea bream were examined in order to select histological slides from specimens in different classes of total length (CT), whose gonads contemplated the different phases of gonadal development of the species. The samples of mackerel gonads were collected between 1998 and 2006 and those of sea bream, between 2007 and 2011, both using handline and troll as fishing gear. The phases and stages of reproductive development were described using the terminology suggested by Brow-Peterson (2011), adapted for each species. For each developmental stage described, the diameters of 80 reproductive cells were measured for mackerel and 80, for dorado at each developmental stage observed. After that, the nucleus-cytoplasm ratio was calculated for the stages. It was possible to describe 11 developmental stages for both species, namely: oogonia, primary growing oocyte - with nucleolar and perinucleolar chromatin, cortical alveolus, vitellogenesis I, II, III, germinal vesicle migration and breakdown, and hydrated oocyte. The formation of lipid vesicles during germ cell development showed distinct characteristics for the species. For mackerel, lipid vesicles were observed to form near the nucleus, while for seabream, this process occurs near the periphery of the cytoplasm. Also, in the gilthead sea bream ovaries, a significant presence of atresic oocytes was observed in active spawning. Despite being found in advanced stages of development, the atresias observed in the gonads presented varied sizes in their diameter. The mackerel oocytes, in turn, showed an increase in their diameter accompanying cell development, with pre- vitellogenic oocytes exhibiting diameters three times larger than those observed in oogonia (p < 2.50e-14). Although to a lesser extent, statistically significant increments were observed for cortical alveolar oocytes relative to pre-vitellogenic (p < 2.708e-14). The mackerel oocyte diameter ranged from 14.08 to 557.22 μm. Mackerel does not show an increase in diameters synchronously until the spawning period, i.e., in the dynamics of cellular organization, there was the presence of oocytes in all stages of development without a dominant phase, characterizing a multiple spawning with asynchronous ovarian development. For gilthead sea bream, pre-vitellogenic oocytes exhibited diameters, on average, more than twice those observed in young cells (p < 2.51e-14). For cortical alveolar oocytes in relation to vitellogenesis III, statistical differences were observed (p < 2.51e-14). The diameter of the gilthead sea bream oocyte ranged from 13.49 to 422.68 μm. The presence of several cells in distinct stages was observed in the ovaries of gilthead sea bream, determining that ovarian development is asynchronous with multiple spawning, characteristic of species that spawn throughout the year. The results of this study offer subsidies for a better understanding of the reproductive characteristics of mackerel and gilthead seabream, species with high economic potential for fisheries.