The beryciform fish Hoplostethus mediterraneus (Beryciformes: Trachichthyidae) is a species discarded from the southern Portuguese coastal fisheries. It is taken as by-catch by deep water trawls, at depths of between 234 and 618 m, more than 80% being taken at depths of between 234 and 422 m. Immature fish ranged from 4 to 13 cm in length and were present at all seasons. Of the mature individuals, males ranged from 7 to 17 cm and females from 7 to 21 cm. From autumn until spring, fish with gonads at various stages of maturation were present, although there were no specimens with mature gonads.