LAUSR

Abstract This study was conducted to assess the physiological parameters of reproduction (sex ratio and gametogenic cycle), parasitism and biological indices (condition index and gonadal index) in Donax trunculus. Samples were collected monthly over two years (from 2016 to 2017) from three sites along the coast of Taghazout (in Southern Morocco) hosting the tourist resort Taghazout Bay. Five stages were depicted by histological examination of gonads: undifferentiated, developing, mature, spawning, and spent. The results of this histological study of the gonads of D. trunculus show that the reproductive cycle of this species has two periods: the first one is characterized by high sexual activity and extends from February to June and the second one corresponds to sexual rest and lasts from July to October. In all three stations and during both years, individuals in the undifferentiated stage (sexual rest) are encountered from July to October. Two spawning periods were observed: the first in March followed by a resumption of activity in April, and the second from May–June. Seasonal variations of the biological indices (GI and CI) were associated with the reproductive and nutritive status of bivalves. The study of parasitism by the trematode Bacciger Bacciger revealed that all the infected individuals were females in the sporocyst stage with a total prevalence between 0 and 9% in August and September respectively. Our results serve as a warning for future management measures and justify the necessity of taking into account the biology of the species in a particular area for better management of resources.