Male and female sand gobies Pomatoschistus minutus (Pallas) from the Oosterschelde (The Netherlands) were examined for the crustacean mesoparasite Lemaeocera lusci (Bassett-Smith) from April to July 1992. Prevalence increased steeply from 4% in April to 80% (females) and 57% (males) in June, The peak abundance of recently attached infective stages (pennella larvae) on sand gobies was found in May, By June, about 70% of parasites were in the post-metamorphosis stage and possessed egg strings. Significant differences in abundance between males and females were found in June but not in May, This may be due to sex-specific differences in behaviour during spawning time. The majority of post-spawning fish probably died in July. Fish of the new year class which were captured in July harboured no parasites.