Preliminary data on gonadal development and fecundity in the Grass goby, Zosterisessor ophiocephalus (PALLAS, 1811) from the Venice lagoon (northern Italy)

Abstract

          This paper reports a preliminary description of ovaries and oocytes characteristics in the grass goby Zosterisessor ophiocephalus from the Venice lagoon across the breeding season. Results allowed identifying of three main oocyte maturation stages occurring in different proportions across the breeding season: immature, ripening and ripe. Shape and size of oocytes change during maturation becoming more elliptical from rounded and increasing in diameter from about 0.2 to more than 0.7 mm. Completely mature ovaries were found in March and April whereas spent females with residual oocytes were present only in June. Fecundity of mature females ranged from 5000 to 26000 eggs and was positively and linearly related with body size. The relationship between number and diameter of eggs suggested a trade-off between these two parameters. Results were discussed in the light of the available knowledge on fecundity and gonadal development of repeat-spawning fishes.