Notes on the Occurrence and Control or the Trematode. 



Gyrodactylus, Ectoparasitic on Fundulus. — By James Nel- 

 son GowANLOCH, B. A., B. Sc, Head of the Department 

 of Zoology, Dalhousie University, Halifax, N. S. 



(Read by Title 11 May, 1925) 



It is the purpose of the present paper to record certain 

 observations on the occurrence and control of the aberrant 

 trematode Gyrodactylus . 



Gyrodactylus is an eyeless, monogenetic trematode be- 

 longing to the family Gyrodactylidae (of which family it is the 

 type genus) occurring as an ectoparasite on the gills, fins 

 and body integument of fish. The animal is extraordinary in 

 that the uterus usually contains sexually mature young which 

 in turn contain another generation and this yet another genera- 

 tion so that as many as four successive generations may be dis- 

 tinguished at one time, one inside another, a situation that 

 might well have been eagerly cited, had it been known at that 

 time, by Charles Bonnet in support of the theory of ^^emboit- 

 mfnt." 



During the progress of other work at the Atlantic Biological 

 Station, St. Andrews, N. B., the writer noted the presence of 

 Gyrodactylus as a parasite on Fundulus heteroclitus L, and subse- 

 quently certain studies of the form were carried out v/ith es- 

 pecial reference to the effect it produced on the host fish, the 

 susceptibilities of the parasite to control measures available 

 in the treatment of the host and choice of host exhibited when 

 various species of fish were made available. It should, per- 

 haps, be pointed out that Gyrodactylus constitutes at times a 

 very serious hatchery problem and measures for its control 

 are therefore of considerable practical interest. 



When first noted Gyrodactylus was observed to occur fre- 

 quently on the fins oi Fundulus heteroclitus. It was found that 

 when these fish were held in aquaria supplied with abundant 

 running sea-water and well fed with Venus mercenaria the tre- 

 matodes multiplied with such rapidity that they most seriously 

 affected the hosts and indeed frequently caused death. When 



