57 



Salting 



Salting i s an ideal trough treatment except for the one 

 limitation that it will not cure everything. In troughs, it is 

 extremely simple to apply; it is reasonably effective against 

 the external protozoan parasites ; it is an excellent tonic to 

 the fish; and its application demands the least accuracy of any 

 known form of treatment. 



There are many ways to salt a fish, some good and others 

 definitely bad. My own choice, which I think as good as any 

 and superior to most, is to determine the volume of water con- 

 tained in a trough -drawn down to a predetermined depth, say 

 two inches. By multiplying the inside length of the trough by 

 the inside width and the product of these two numbers by the 

 predetermined depth, all expressed in inches, one obtains the 

 water content in cubic inches. For each 60 cubic inches of 

 water in the trough at this predetermined depth, one ounce of 

 finely ground salt is dissolved in a pail half full of water. 

 To administer the salting, shut off the inflowing water, drain 

 the trough to the predetermined depth, and spread the salt 

 solution from the pail evenly over the trough. 



Fingerling trout will withstand this concentration for six 

 to ten minutes. When several of the weaker fish have turned 

 over, the inflow is resumed at the maximum rate which the fish 

 will withstand and the drain partially opened to permit a rapid 

 replacement of the salt water. This method may be applied to 

 fish as often as desired without apparent injury and, indeed, 

 with a definitely tonic effect. When repeated three times at 

 24 hour intervals, salting is quite effective in curbing epidem- 

 ics caused by external protozoans and it is the only treatment 

 which should ever be applied in the absence of definite knowledge 

 regarding the cause of any mortality. Salting, however, becomes 

 progressively more expensive, less effective, and more difficult 

 to apply as the size of the body of water to be treated increases. 



Flushing 

 Regarding the second method, namely flushing, which is used 

 primarily as a preventive, very little is known - far too little 

 to justify much comment. The method consists in routinely 

 adding several fluid ounces of disinfectemt solution of definite 

 strength to the upper end of a trough and allowing it to flow 

 down the trough and out. This method may have distinct pos- 

 sibilities. At least as now usually applied it does not appear 

 to be toxic to the fish. However, in my own experience at 

 least, on the only occasion which has come to my attention this 

 method of applying copper sulphate solution definitely did not 

 prevent an epidemic of Gyrodactylus . Unquestionably, this 

 method should be further investigated under controlled conditions. 



