1880.] 



MICEOSCOPICAL JOUENAL. 



103 



The Salmon Disease and its 

 Cause.* 



Some analogy seems to exist 

 between the spread of the fungoid 

 disease, at present so destructive to 

 sahnon life, and the apparently, 

 erratic dissemination of ordinary 

 zymootic disorders, which, in their 

 origin, many probably be all refer- 

 able to violations of natural laws. 



Unlike the more subtile charac- 

 ter of many epidemics affecting the 

 human family, or even the rinder- 

 pest among cattle, the vegetable 

 parasite — Saprolegnia ferax, at 

 present developing itself with such 

 unprecedented rapidity, and such 

 mischievous results upon fish in 

 English rivers, is of sufficient size 

 to be studied by the ordinary 

 powers of the microscope, and its 

 growth may be followed from the 

 germination of the infusorial spore, 

 with a 1^ or |-inch objective. 



The causes ascribed to account 

 for this hitherto unknown outbreak 

 among salmon are various, but 

 mostly point to river pollution. 

 So far as I am aware, however, 

 they do not indicate any consider- 

 able change of condition or cir- 

 cumstance to which the fish have 

 been subjected of late years. 



The proximate cause of this 

 disease and the reason wliy its 

 ravages should extend so rapidly at 

 this time, is a question of sufficient 

 interest and importance to arrest 

 the attention of all interested in the 

 preservation of our most valuable 

 iish — one of the most important 

 sources of food supply. Not that 

 the fungus restricts its attacks to 

 salmon, for many fresh-water fishes 

 are destroyed by it, and even newts, 

 tadpoles and fresh-water mollusca 

 are sometimes attacked ; this is well 



♦A paper read by M. A. Robson, Hon. 

 Secretary, before the members of the North 

 of England Microscopical Society, March the 

 17th, 1880. 



known to those who have aquaria, 

 for despite all ordinary care, it 

 sometimes happens that the fin- 

 ny favorites become fluffy and 

 mouldy, the fungoid pest irritates 

 and destroys the skin, until, seizing 

 upon the gills, the tortured animd 

 can resist the attack no longer, and 

 is soon found dead — the fungus 

 developing rapidly over it in woolly 

 tufts. 



Among salmon in rivers this 

 pest first appeared so recently as 

 the spring of 1878 in the Carlisle 

 Eden, the Annan, the Mitt and the 

 Lancaster Lune, where large num- 

 bers of spawned fish ( Kelts ) and 

 also some salmon, smelts and 

 trout were found in pools and 

 floating down the stream, dead or 

 dying. Nearly twenty years ago 

 those engaged in cultivating the 

 ova of trout and salmon found 

 these attacked by a vegetable para- 

 site which effectually destroyed 

 their vitality — they were also to a 

 considerable extent cultivating and 

 disseminating the fungus itself. 

 Mr. F. Buckland thus describes the 

 appearance of salmon killed by this 

 disease " they are all more or less 

 covered with patches of fungus, 

 generally circular in form. The 

 tail is almost always affected, and 

 often to such an extent that the 

 soft parts are eaten away and the 

 bony rays left quite uncovered — a 

 bunch of fungus is generally found 

 growing on the head and nose, and 

 hence the diseased fish in the Eden 

 are called 'salmon with white 

 nightcaps.' " 



Many years ago the Kev. M. J. 

 Berkely instanced the genera 

 Achlya, Saprolegnia, Pythia and 

 Aphanomyces as "notoriously an- 

 tagonistic to animals, especially 

 those of aquatic habits in a low 

 stage of vitality ;" of these the genus 

 Saprolegnia appears to be most 

 inimical to salmon life. On ac- 



