SEA-FISHERIES LABORATORY. 155 



XOTE ON AN ULCERATIVE DISEASE OF THE 

 PLAICE. 



By W. Riddell, M.A., Fisheries Assistant, Zoological 

 Laboratory, Liverpool; 



AND 



D. Moore Alexander, M.D., School of Public Health, 

 Liverpool. 



(With Two Plates.) 



History and Characteristics. 



For some years past the stock of spawning plaice at 

 the Port Erin Hatchery has been subject to a disease, 

 apparently infectious, which has done much damage. 



The plaice are kept in two large oj)en-air ponds, 

 which together occupy a space 90 feet long by 50 feet 

 wide, with a total capacity of about 130,000 gallons. 

 The number of fish in the ponds varies from about 800 

 to 400 or more; the average number is roughly 350. 

 Disease seems to have made its appearance first in 1905 ; 

 at any rate no diseased fish were observed before that 

 year. It has been more or less constantly present ever 

 since ; in 1910 there was less disease than in any other 

 year since 1905, but in 1911 many of the fish in the pond 

 were affected. 



The disease is characterised by superficial ulceration 

 (see PI. I), which seems to have no very characteristic 

 site, though possibly ulcers are more common on the top 

 of the head and at the base of the tail. Still we have 

 seen ulcers on so many different parts of the surface that 

 we cannot regard any position as typical. The ulcers 

 are of a spreading and sloughing type, leading to con- 

 siderable destruction of tissue and often extending down 

 to the muscular layer. They vary in size up to about 



