5 



is marvellous, and requires to be seen at work to be properly 

 appreciated. There is a little filter attached to each jet, but, 

 I may add, this is not an essential point. Fresh water 

 requires adding from time to time to make up for loss from 

 evaporation, and if there are many Crustacea in the tanks, a 

 piece of chalk must be kept in one of the reservoirs to com- 

 pensate for that abstracted from the water for shell making. 

 Having now described in general terms the arrangement of 

 my aquarium, I propose from time to time to give notes of 

 any interesting objects which we may be studying. 



No. II. 

 FISH PARASITES. 



(Re-printed from "Ashore or Afloat ," for September 28th, 1883.) 



In July last Mr. John T. Carrington, F.L.S., of the Royal 

 Aquarium, Westminster, called my attention to the extreme 

 abundance of a parasitic crustacean in the fr jsh water tanks 

 of that Aquarium. At one time the little creatures appeared 

 in such quantities as to quite obscure the fish in the tanks, 

 and the havoc which they created amongst the fish was 

 something astounding. The little crustaceans belonged, 

 undoubtedly, to the genus Argulus, but appeared too large 

 for our British species A. foliaceus, Linn. They were of a 

 pale blue green colour, and sufficiently transparent for the 

 general anatomy to be made out with the aid of a microscope. 

 There were many specimens over half an inch long, and it 

 was their unusual size which first made me doubtful as to 

 the species being A. foliaceus. The parasites attached them- 

 selves under the scales of the fish by means of their two 

 large suckers, bringing on inflammation, and later a macer- 

 ation of the surrounding tissues, so that the spot occupied by 

 each individual appeared as a small raised white patch. All 

 species of fish in the tank were attacked alike, and an im- 

 mense mortality resulted. To show the rapidity with which 

 this was accomplished, I am informed that a 16-lb pike was 

 killed in three days. Mr. Carrington, knowing that many of 

 these fish parasites cannot live in salt water, had some of the 

 fish bathed in strong brine, and immersed in sea-water for a 

 short time. Others methods were tried, including the 

 reduction of the temperature of the water with ice. The 

 results, however, were not very satisfactory, for though the 

 attached parasites were usually killed by the salt water treat- 

 ment, others soon attached themselves, and matters were as 

 bad as ever. The most successful method tried by Mr. 

 Carrington, and indeed the one by which he succeeded in 

 getting rid of the pest, was the introduction of a large number 

 of very fine sticklebacks (Gasterosteus trachnras). These fish 



