188 



On the Fish Parasites, Lepeophtheirus and Lernjea. 

 By Andrew Scott, 



Resident Fisheries Assistant at the Piel Hatchery. 

 (With five Plates.) 



Introduction. 



There are comparatively few fishes that do not, at some 

 period of their life history, prove on careful examination 

 to be the host of at least one kind of parasite, either crus- 

 tacean or worm. The worm parasites are usually found 

 infesting the alimentary canal (Nematodes and Cestodes), 

 the gills and skin (Trematodes and Bdellodes), while 

 Crustacean (Copepod) parasites are almost entirely con- 

 fined to places in direct communication with the exterior, 

 such as the skin itself, the fins, the mouth, the branchial 

 chamber, attached to the gills and operculum, in the 

 nostrils, and in the mucous canals. They may even be 

 found attached to the eye, as Lemceenicus sprattce in the 

 sprat (Clupea sprattus) ; and Lemceopoda elongata in the 

 Greenland Shark* (Ac author hinus carcharias), causing in 

 the latter at any rate partial blindness ; or burrowing into 

 the abdominal cavity, as Penella exocoeti in the flying 

 fisht (Exocoetus volitans), till only the ends of the ovisacs 

 are visible from the exterior. 



The Copepod fish parasites have attracted much atten- 

 tion from Zoologists for a very long period, since the time 

 when Aristotle, in his tk Historia Animalium," tells us 

 that the tunny and the sword fish are tormented by a sort 

 of worm which fastens itself under the fin. Many of 



* Mr. R. L. Ascroft, of Lythani, who visited Iceland on a " steam liner," 

 fishing for halibut, &c, a year or two ago, says nearly all the sharks caught 

 on the lines had these parasites in their eyes. 



f One was exhibited at a meeting of the Liverpool Biol. Soc. in 1897, 

 infested by two such parasites, recorded as P. blainvilli, which in turn 

 were covered with a number of small Cirripedes. — Trans. L'pool Biol. Soc, 

 vol. xi., p. xii. 



