Sexuality and gonadal cycle of the common dentex ( Dentex dentex) in intensive culture

Abstract

The common dentex ( Dentex dentex) is a highly valued table fish in the Mediterranean region. In culture conditions, this sparid fish has a high specific growth rate and spawns spontaneously. However, the proportion of females that spawn spontaneously and the timing of their spawning are highly unpredictable. In addition, knowledge of the sexual cycles of this species is very limited. The main objective of this study was to provide basic knowledge on the reproductive biology of the common dentex. Study of male and female gametogenesis was performed using four groups of 0 +-, 1 +-, 2 +- and 3 +-year-old fish born in captivity. These groups were sampled either every 1 or 2 months, for either 1 or 2 consecutive years. Histological analysis of the gonads from a total of 448 individuals enabled the definition of five maturity stages for male and five for female fish. Sexual differentiation occurred between 5 and 12 months of age. Among the fish studied, neither bisexual gonads nor any other indication of sexual inversion was found in fish up to 4 years of age, suggesting that common dentex is a gonochoristic fish. In Crete, Greece, spawning took place between the end of March and May. Males and females older than 1 year (1 +) matured almost simultaneously. All the 2-year-old males produced milt. In our sampling conditions, the highest percentages of females observed undergoing maturation during their second, third and fourth years were 67%, 100% and 100%, respectively. Sexually mature females were detected at the minimum standard length of 21 cm. After the spawning period, and until the following January, all the females were in previtellogenesis and in some males, spermatogenetic activity resumed gradually. In February, under increasing photoperiod, cortical alveoli appeared in growing oocytes and the development of spermatogenesis greatly increased. Between February and April, vitellogenesis occurred in females and the gonadosomatic index (GSI) increased from 0.2–1% to 3–6% in both sexes. The fecundity estimates indicated that common dentex display a spawning strategy similar to many temperate marine teleosts. It is a multiple spawner, exhibiting asynchronous oocyte development (unknown annual fecundity). Batch relative fecundity ranged from 32,000 to 393,000 eggs/kg body weight, and a positive linear relationship between batch fecundity and body size was found.