MANUAL OF FISH-CULTURE. 63 



all Aveighed, and it was found that lot c bad made a slightly better 

 growth than lot a. 



One of the most uncontrollable diseases attacks salmon fry midway 

 in the sac stage, and iinishes its work before the complete absorption 

 of the sac. The most evident symptom is the appearance of scattered 

 white spots in the sac; the fish cease to try to hide, but lie scattered 

 about on the bottom of the trough ; the spots increase in size, coalesce, 

 and finally occupy large areas, especially in the tip of the sac, which 

 becomes quite white. Soon after this the fish dies. The attack on a 

 lot makes rapid progress; for instance, a lot of 2,000 in which, up to 

 April 22, the losses have been from 1 to 9 daily, will show 17 dead on 

 the 23d, and five days later 360 die in a single day. In 1890 this epi- 

 demic attacked especially the fry of Atlantic salmon, destroying about 

 a third of them; it also destroyed many landlocked salmon, and some 

 other species suffered heavily about the same time. In 1891 there was 

 not a trace of it. In 1892 it returned again, and out of 305,353 fry of 

 Atlantic salmon it left but 3,874, and these were by no means healthy ; 

 but it attacked only Atlantic salmon. Salt and mud were tried as 

 remedies, but though the progress of the disease appeared in some 

 instances checked thereby, no permanent benefit resulted from their 

 use. 



In 1890 this epidemic appeared to run in families. There was evi- 

 dence tending to show that all the eggs coming from a particular mother 

 would have a common degree of liabilitj^ to the disease — some families 

 being exterminated by it, some only decimated, and others able to resist 

 it altogether. It did not appear to be infectious, as several lots of fry, 

 separated by screens, would occupy a single trough, and in some cases 

 those at the head of the trough would be totally destroyed, or nearly so, 

 and those below them escape from attack. 



The only other diseases of Atlantic salmon that demand notice here 

 are connected with the so-called fungus, belonging to the group of 

 water molds called Saprolegnice^ and probably to the genus Sajnolegnia, 

 one species of which, S.ferax, is noted as the cause of very destructive 

 epidemics among the adult salmon of Scotch and English rivers. The 

 species that attacks fish eggs is well known to every flsh-culturist as 

 a fine white growth of a cottony or woolly appearance that forms upon 

 dead eggs, and when neglected spreads out so as to envelop in its 

 threads a great many of the living eggs surrounding it. It is by no 

 means certain that all such growths belong to one species or even to 

 one genus, but they are much alike in structure and growth and live 

 upon animal and vegetable matter, either as parasites attacking living 

 matter or as saprophytes attacking only dead and decaying matter. 

 There has never been serious trouble with this fungus at Craig Brook 

 station, and great loss from it can only occur in consequence of neglect 

 of the duty of picking out the dead eggs. An instance of its attacking 

 a living Qgg except by reaching out from a dead one is unknown. Fish 



