Blennius ocellaris; Print; The butterfly blenny (Blennius ocellaris) is a small marine blenniid fish of Northern and Western Europe; as well as the Mediterranean and Black Seas and Morocco. It can grow as large as 20 centimetres (7.9 in) in length. It is usually found at a depth of 10-400 metres (33-1; 312 ft) down; especially in areas with a rocky floor.; 1700-1880