Estratégia reprodutiva da caraúna-azul Acanthurus coeruleus Bloch & Schneider, 1801 (Perciformes: Acanthuridae) capturada no litoral norte de Pernambuco

Abstract

The species Acanthurus coeruleus (Bloch & Schneider, 1801), popularly known as the blue tang, is a reef fish belonging to the Acanthuridae family, which is geographically distributed from the eastern coast of the United States to the southeast of Brazil. In the Brazilian northeast coast this species is a component of artisanal fishing, being captured mainly with traps, and much of its production has been destined for export. Although there is no quantitative assessment of catches available for that region, the species has been identified as frequent in landings. Considering, therefore, the economic potential of this fishery, the objective of this study was to determine the reproductive strategy of the blue tang fish captured in the north coast of the state of Pernambuco. The specimens were collected monthly between January 2013 and December 2016. For each individual collected, the total length in centimeters, total weight, eviscerated weight and gonads weight in grams were recorded. The gonads were classified macro and microscopically as to sex and maturational phase. The frequency of males and females was used to establish the sexual proportion, and the length structure was based on the distribution of the length frequencies in classes of 3cm. The weight-length relation was estimated for males and females from the equation PT = aCTb. Spawning frequency estimates were obtained from the hydrated oocytes (HO) and post-ovulatory (FS) follicles method, and the reproductive cycle of the species was determined from the monthly proportion of females at each gonadal maturity stage and by monthly evolution of the gonadosomatic index, calculated from the equation: IGS = (PG / PE) x 100. To determine the pattern of development and recruitment of oocytes and the type of fecundity, 68 specimens of females sampled during the months of greatest reproductive activity of the species (August to January). The portions of 0.04g of gonads in the development stages, able to spawn and active spawn were dissociated and the oocytes counted and measured, in order to determine the frequency distribution of the oocytes and the prevalence of oocyte stages in each of these stages of ovarian maturation. In total, 496 were shown, of which 235 were males and 261 females. The sex ratio was 1.11 females for 1 male and did not differ significantly between the sexes. The length frequency distribution varied between 14 and 41.7 cm, with predominance of females in the classes 24 to 32 cm and of males in the classes 26 to 32 cm. The estimated allometry coefficient (2.76), suggests negative allometric growth for the species. According to the IGS and the histological analysis of the gonads, the reproductive period extends from July to January, with periods of greater reproductive activity as of August. The fecundity of the lot ranged from 20.000 to 55.000 oocytes, and estimates of spawning frequency by the hydrated oocyte (HO) method indicated that the species spawned once every 3.8 days, and according to the follicle post ovulation (POF), spawning takes place every 3.4 days between August and January. The frequency distribution of the oocytes was continuous throughout the developmental stages, and the variation in the percentage of oocyte cortical and total vitellogic alveoli remained relatively constant between the maturation phases and during the spawning period. The seasonal variation of the Vtg3 oocyte diameter in ovaries at the spawning stage did not show significant differences during the months of reproductive activity. Thus, these results indicate that the species shows asymptotic development of the oocytes, split spawning and indeterminate fecundity model.