Ill 



in laying hold of its victim, is far more deadly, and will flourish where the MR. 0. L. 

 other cannot gain a footing. Pollution may aggravate it, and also overcrowd- JACKSON. 



ing, but they are not necessary to its existence. Our tanks are so clear a pin 



can be seen through 14 feet of water, and, except for this disease, every fish is 

 in grand condition ; but in spite of all this it remorselessly seizes fish after 

 fish, and all die. 



The appearance of the disease is very different ; the ordinary fungus is more 

 fluffy, stands up higher, and the fish does not appear distressed. The 

 Saprolegnio, is a more compact mass, more like blotches of velvet, but with a 

 soreness that gives it the appearance of some scrofulous affection. The out- 

 line of the blotches is more sharply defined. The fish seem very much 

 distressed, and when it fairly gets hold waste away to nothing. The fungus 

 also is more firmly attached. The points 1 should have liked to have more 

 time to work out, are : 1st. Whether all freshwater fish are subject to it. It is 

 rather singular, our roach, dace, gold-fish, gudgeon, and crucian carp, though 

 exposed to the full infection, show no sign of taking it, yet these fish are 

 peculiarly subject to the aquarium fungus. The large carp which came with 

 the tench had some of it growing on them six months since, but do not seem 

 to care about it, while all our tench and golden tench are dead or terribly ill, 

 the trout are gone, and the char are fatally struck. 



2nd. Whether a change to salt water will cure it. We have several 

 migratory trout in our freshwater tanks, but at present it has not struck 

 them. They have been with us a long time, and are in grand condition. 

 When it attacks them, as soon as it is fairly developed they will be put in sea 

 water and the result observed. I fear, however, this hope must be abandoned. 

 We have in one of our sea-water tanks two splendid sea-trout. They came to 

 us a few ounces in weight about two years since, and are now several pounds 

 in weight. They have not been in fresh water since they came, but one of 

 them I fear is affected. During the last month he has got blotches precisely 

 similar in appearance on his head, side, and tail, and they are rapidly spreading. 

 He does not, however, yet show much falling off in condition, probably . 

 because the disease has not attacked his gills. I could not examine him 

 microscopically, for it is important to watch the disease and see whether (if as 

 I am almost sure it is the same) its effects are the same in the sea as in the 

 land. Lastly, I want to ascertain the exact locality from which the infected 

 fish came : that I have not yet been able to accomplish. I think it is clear 

 that the disease is highly infectious, is not produced spontaneously, but is 

 imported, as it clearly is in our case. Our tanks are isolated from one another 

 in the building, but overflow through one pipe into the reservoir some 30 

 yards away. The water is then drawn to pumps in engine-house and pumped 

 lip. The spores to infect all the tanks must have gone all this round, and 

 through the pumps. If the sea-trout is attacked (as I believe) by the same 

 disease, the spores must also be capable of being carried through the air, 

 as there is no connexion between the tanks. I think they must also have a 

 high vitality in sea-water, for the tank where this fish is, is right at the 

 opposite end of the place, and a thick wall is between it and a freshwater 

 tank. The probability is that the spores would fall in the nearest tanks, in 

 which case they must have gone through the whole circulating system, and 

 affected all the tanks before they reached the one where the trout is. (The 

 disease has, however, not attacked any other fish in salt-water.) If this is so, 

 the disease may be spread by salmon from different rivers meeting in the sea, 

 and also may be carried through the air from river to river. While I do not 

 think microscopic observations alone are sufficient, I by no means despise 

 them, my reason for wishing to observe the progress of the disease is the great 

 difficulty of accurately distinguishing some of these low organisms merely by 

 their micro appearance. In this case, however, the two fungi are very distinct. 

 The engraving Mr. Walpole sent me from the " Field " is very good of the 

 Saprolegnia, but it is very unlike the other. In Saprolegnia the spore cases 

 appear like thickened fibres, some with a nob at the end, full of spores. In 

 the other the spore case is almost like a short pea pod, borne at the end of a 

 long and very thin stalk. I hope, however, to show you this so that you may 

 judge for yourself. 



As regards cure, I see nothing that can be done except to try to make our 

 rivers more healthy, and rigorously destroy and burn every infected fish. We 



