112 



MR. C. L. 



JACKSON. 



must then hope that the disease will run its course speedily, and disappear as 

 epidemics usually do. I must, however, reserve giving an opinion until I 

 have had time to watch it still longer, and to work out the points indicated 

 above. 



I have, &c. 

 Hill Fold, Bolton, C. L. Jackson. 



June 20, 1880. 



MR. HENRY 

 LEE. 



III. — Letter from Henry Lee, Esq., F.L.S. (formerly Naturalist to the 



Brighton Aquarium). 



Gentlemen, 



In accordance with your request, I send you a few remarks on the 

 fungoid disease of salmon. It is unnecessary for me to enter into details, as 

 the subject has been carefully and fully treated of in various reports which you 

 have received, notably in that by Dr. M. C. Cooke, who is our chief authority 

 on microscopic fungi. Saprolegnia ferax, the fungus which is the cause of the 

 so-called " salmon disease." has long been well known. It is the same fungus 

 which attacks other fishes in fresh water. Its identification is not difficult, 

 and the descriptions of it by Dr. Cooke, Professor Roileston, Mr. Worthington 

 Smith, See., may be accepted as conclusive. I have not seen the reports of the 

 two gentlemen last named, but I am glad to perceive that Dr. Cooke asserts 

 that which the experience of some years as naturalist to the Brighton Aquarium 

 has led me to maintain, namely, that this fungus will not attach itself to the 

 uninjured skin of a healthy fish. A variety of circumstances, and, in my 

 opinion, especially overstocking, may cause the salmon to lose its healthy tone 

 and vigour, and to lapse into a constitutional condition favorable to its becom- 

 ing the recipient of the disease ; and any healthy salmon whose dermal 

 membrane of either the scales, head, or fins, may be injured or abraded is 

 instantly laid open to its attack. I have seen this exemplified in a remarkable 

 manner in fresh-water fishes, such as carp, roach, &c, brought to the Brighton 

 Aquarium after having been taken by a net. Wherever a knot of the net had 

 pressed on the fish and bruised the cuticle of the scales, there a tuft of 

 fungus would soon become apparent, and it was curious to see these tufts 

 growing for a day or two at equal distances from each other — the distance from 

 knot to knot of the net in which they had been caught. By vigorous oxygena- 

 tion of the water, healthy strong fish, which had been but little hurt, would 

 recover and get rid of the fungus entirely as their skin healed. Unhealthy, 

 exhausted, and severely rubbed fish died after the fungus had established 

 itself beneath their scales. 



At first we tried to free the fish from this fungus by removing them to a 

 stream of running water, but as this involved their capture in the landing net, 

 and, consequently, fresh abrasion of their scales, we soon found that this made 

 matters worse. The best remedy we then knew of was to leave them 

 untouched, and invigorate them with as much oxygen as possible by well 

 aerating the water. We afterwards discovered that immersing affected fish for 

 a few seconds in salt water, or lightly sponging them with it, frequently cured 

 them, and destroyed the fungus in cases where its mycelium had not obtained 

 too firm a hold. 



Briefly, then, my opinion is, first, that the spores of Saprolegnia ai'e con- 

 stantly present in both pure and impure water (though more abundantly in the 

 latter), and ready to attach themselves to any surface suitable to their growth. 



2ndly. That a strong and healthy salmon, the dermal membrane of which 

 is in every way uninjured, does not furnish any such suitable surface, and is 

 impervious to the fungus. 



3rdly. That a salmon is in a condition to become the recipient of the fungus 

 when from any cause its vitality is lowered, when it is weak and out of health ; 

 and also when any portion of its cuticle has been abraded, even if the fish be 

 in good health. 



