Observations on the biology of the marine Leech Oceanobdella blennii

Abstract

The biology of the marine leech Oceanobdella blennii, ectoparasitic on the littoral fish Blennius pholis, was studied on the coast of North Wales from 1964 to 1966. Leeches first appeared on the fish in large numbers in December, but were less common in January. During February and March they became more abundant on individual fish and among the host population as a whole, but in April and May the leeches began to disappear and none was ever found from June to November.