62 Proceedings, 



they seem indifferent to. I never saw a Tench or a Carp 

 affected. Eoach, Dace, Bleak, Charr, and Goldfish are sin- 

 gularly liable. Gudgeons are very free, Chub less so. Of 

 course I refer to these fish under comparatively altered con- 

 ditions, such as change from a river to a pond or tank, with 

 the accompanying change of temperature. I will close my 

 list of instances by a reference to fish hatching, though if it 

 were proved that Saprole(jna attacked the ova it would be 

 plain that change of temperature is not the sole cause of its 

 appearance. The ova in my experiments were subject to two 

 fatal maladies, one of which changes the ovum from trans- 

 j)arency to white opacity, and the other furs it over like 

 mould. This mould glues the ova together, and is fatal. It 

 does not quite resemble Saprolei/na ; and I do not think that 

 Mr. "Frank Buckland describes it minutely, though he notices 

 it as an enemy. The other ailment is probably simple death 

 from weakness, unaerated water, or the punctures of the 

 Water Shrimp. 



Eeturniug to the Salmon, what do we find ? On the Tay 

 and all the chief Salmon-rivers of Scotland there is at times 

 a large mortality ; these fish are all affected by Saprolegna. 

 The disease runs its course in autumn and winter, and the 

 fish lie dead on the banks by hundreds. The explanations 

 are manifold — changes from salt-water to fresh ; overcrowding 

 in the weir pools, where fish congregate at the foot of the 

 weir to await a flood; fighting amongst the males; exhaustion 

 from travelling so far ; snowbroth, &c. With regard to the 

 crowding — Why is there not the mortality every year ? and 

 this would also dispose of the fighting theory, the salt water, 

 and the exhaustion. In the great Canadian rivers of the 

 West Coast the Salmon are in such multitudes in their 

 migrations that they are said to shoulder each other out of 

 the water ; on such a scale the death-rate from overcrowding 

 should be tremendous, and fi-om exhaustion frightful. The 

 snowbroth theory has more to recommend it, but it would 

 require careful tables year by year to prove the case. This 

 would also be included under the general head of change of 

 temperature. That snowbroth is excessively disliked by 



