130 SAPROLEGNIA EPIDEMIC. 



gills and thus impede aeration. When we consider thfr 

 effect of the parasite destroying the tissues, we can readily 

 understand why death soon follows. The presence of 

 haemorrhage clogging the gills would accelerate the result. 



Much has been written regarding the parasitism of 

 Saprolegnia, but it is generally admitted that the fungus is 

 a saprophyte and a facultative parasite, i.e., it can become 

 parasitic when circumstances are favourable. Such would 

 occur if the fish be weakened in any way, either by sickness,, 

 by lack of food, by unsuitable surroundings {e.g. stagnation 

 of the water, excessive fungoid or bacterial life depleting 

 the oxygen supply), or by injury to the skin, whether 

 caused mechanically or resulting from invasion by animal 

 parasites. The rapidity with which the fungus extends- 

 over the affected fish dei:)ends especially on the resistance^ 

 of the host's s.kin and to a less degree on the temperature. 

 Healthy fish in suitable surroundings are apparently not- 

 affected. 



In freshwater hatcheries and aquaria Saprolegnia may- 

 become a very serious pest, consequently all conditions- 

 which interfere with healthy fish life — such as those- 

 mentioned above — should be guarded against, diseased and 

 dead fish and insects should be removed, since the fungus- 

 is able to fructify on these. 



As remedies for infected fish, Hofer mentions a number 

 of solutions- — 10 per cent, saline, .01 per cent, sublimate, 

 .01 per cent, magnesium sulphate, zinc or copper sulphate^ 

 weak boracic or salicylic acid, 1 per cent, potassium per- 

 manganate. These should be applied by means of a sponge- 

 to remove and destroy superficial hyphse and sporangia but 

 the more deeply situated mycelium is still capable of re- 

 production. Sometimes fish are placed for half an hour 

 in a bath containing one grain of potassium permanganate 

 in 100 litres of water, aeration being resorted to during th& 

 bathing operation. This quantity of solution is said to be 

 sufficient for ten pounds of fish. In the case of diseased 

 salmon, their removal to the sea is known to destroy the 

 fungus. 



When small ponds are infected it has been recommended 

 that they be drained and then disinfected by using lime 



