This report details the development of a microsporidan infection in a colony of seahorses (Hippocampus erectus) caused by Glugea heraldi. Of 76 animals imported from Florida Bay (USA), two survived. A myxosporidan (Sphaeromyxa sp.) and an unidentified nematode infection were also diagnosed in the same colony, but these infections were not considered important, causative factors in the mortalities.