Fish and Fish-Leeches on Rocky Shores Around Britain

Abstract

Collecting water from rock pools just above rising tides, usually in winter and spring, yielded 1412 Lipophrys pholis, 255 Pholis gunnellus and 29 Coryphoblennius galerita, bearing respectively 172, 8 and 1 Oceanobdella blennii, 744 Taurulus bubalis bearing six Oceanobdella microstoma and 14 Sanguinothus pinnarum, and a Myoxocephalus scorpius with a single O. microstoma; fishes of 23 other species totalled 1243, but none bore leeches externally. Oceanobdella blennii was found mainly in February and March (some in gill chambers), at temperatures generally below 8°C, with lower numbers (all external) in April and May and none later. Infestation was highest in Northumberland. Leeches on P. gunnellus were smaller than those on L. pholis, which they would not attack. They were confined to Northumberland and Scotland, where L. pholis was scarcer. The southern limit of O. blennii seemed to be in north Cornwall, but O. microstoma, though more stenothermal, extends from the Arctic to south Devon, its hosts living mostly subtidally. It is hidden under the chin of Cottidae, whereas S. pinnarum is easily seen on the fins. Abundance in south-west Britain of the ‘cleaner fish’ Crenilabrus melops may explain why S. pinnarum, though common in Scotland and tolerant of summer temperatures, is scarce in Anglesey and not found further south.