Reproduction and fecundity of Donax trunculus L., 1758 (Bivalvia: Donacidae) in the littoral of Malaga (Southern Spain)

The reproductive cycle and fecundity of Donax trunculus Linnaeus, 1758 was studied using histology and changes in flesh dry weight, in the littoral of Malaga (Southern Spain), from February 1990 to January 1991. The high levels of chlorophyll, attributable to the occurrence of upwellings, and the relatively temperate temperatures of the seawater on the littoral of Malaga allow a long reproductive period, from February to October, and facilitate the maintenance of the gonads of many individuals in a preactive stage from November to January. The highest percentage of individuals with cytolized stages (44%) was found in January. Histological study of the sexual cycle shows continuous spawning from April to September, with two peaks in May and August. Between these months, there is an important amount of early active individuals, which proceed from postactive without having gone through a cytolized stage. Data on the fecundity, measured as total number of oocytes, have been obtained with the help of image analysis techniques on series of histological preparations of active females. The average size of the mature oocyte, considered as an ellipsoid, is independent of the size of the individual. The ratio of gonadal volume to visceral mass volume ranges between 13.42 and 51.46, being lower in the second peak of spawning for individuals of similar size. The percentage of the gonadal volume occupied by the oocytes ranges between 9.67% and 20.28%, being lower in females of similar size from both August and September. The two latter results and the histological observations support the hypothesis of two spawnings per individual in each cycle, the second of which would be reduced in intensity. The total fecundity for D. trunculus ranged between 33,245 and 641,000 oocytes.