Cocoon deposition on three crab species and fish parasitism by the leech Notostomum cyclostoma from deep fjords in northern British Columbia

Abstract

Cocoons of the sanguivorous piscicolid leech Notostomum cyclostoma (Johansson) were found on 3 crab species, Lithodes aequispina, Paralithodes camtschatica and Chionoecetes bairdifrom deep fjords in the Portland Inlet system, northern British Columbia, Canada. This leech-crab association is convenient for cocoon deposition and dispersal. The leech does not appear to harm its crab hosts. Gut contents of N. cyclostoma collected off the crabs were fish-blood meals in various stages of digestion. The haemoflagellate Cryptobia sp. was observed in gut and proboscis area of 90 % of the leeches. One leech harbored another haemoflagellate, Trypanosoma sp., in its gut. Cryptobia sp. and Trypanosoma sp. were observed in the blood of 29 % of yellowfin soles Limanda aspera from one fjord. No haemoflagellates were observed in 7 other fish species caught coincidentally with the crabs. L. aequispina was the most cocoon-infested crab species. In Observatory Inlet, where L. aequispina was least common, more cocoons per crab were recorded than from the other fjords, Alice and Hastings Arms. Crabs which had not moulted for some time carried more cocoons than those with newer shells. This was less marked among C. bairdi subject to the exoskeleton disease of Black Mat Syndrome on older shells. The most used cocoon deposition site on crabs was the carapace, followed by the merus segments of the posterior limbs.