58 



Dipping 



The third basic method, hand dipping, could be the subject 

 of several closely written volumes. Suffice it to say that this 

 method is a dangerous one for the solutions used are powerful 

 and relatively concentrated, hence the difference between an 

 effective dose and a killing one is exceedingly narrow in viev 

 of our present lack of knowledge concerning this very common 

 method of treatment. When applied with extreme care, it un- 

 doubtedly may be of great value in controlling epidemics of 

 external parasites and certain types of bacterial diseases such 

 as fin rot, ulcer disease, and the eastern type of gill disease. 

 . . . Certainly, hand dipping should never be applied to anj large 

 number of fish unless there is valid reason to believe that 

 some external parasite is causing the losses. In the absence of 

 such reason, a dip should be applied to a small number of fish 

 as an experiment. If the percentage loss on this isolated group 

 does not fall significantly below that of the entire group of 

 affected fish within two days after the experimental treatment 

 was administered, that method of treatment should be foregone. 



As for the exact technique of hand dipping, in my opinion 

 it is best done in a dipping box. This apparatus fixndamentally 

 consists of a solidly constructed, watertight, wooden box, in 

 cross section about two inches narrower than the hatchery troughs, 

 about half again as deep, and approximately three feet long. The 

 box is legibly marked at the height attained by a known volume 

 of water. In this dipping box is slung am inner compartment, 

 resting onfour "ears" which are sufficiently wide to rest on the 

 top of the dipping box, yet sufficiently narrow to slip into the 

 hatchery troughs. This inner compartment is made from two wooden 

 sides, rounded vertically at the ends and the bottom is covered 

 with a coarse mesh galvanized wire covering. The galvanized 

 mesh, in turn, is covered with bobbinet on the inside, the bobbinet 

 being caught to the wire mesh at a sufficient number of points 

 to keep the bobbinet from floating off. 



In use, the desired quantity of disinfectant is weighed 

 out and dissolved in the box filled to the calibration mark. 

 The inner compartment is then placed in the trough containing 

 the fish to be treated, where a convenient number of fish may 

 be placed in it from the trough by means of a scaff net. The 

 compartment is then removed to the dipping box and the fish 

 immersed in the disinfectant. After the requifed time for the 

 dip has elapsed, the inner compartment is carefully lifted fron 

 the dipping box and immersed in the trough to contain the treated 

 fish. By slowly lifting the "upstream" end, the fish slip out 

 of the "downstream" end. The solution in the dipping box should 

 be aerated constantly and renewed frequently. Needless to say, 

 the temperature differences between the infected trough, the 

 dipping box, and the treated trough shouldat no timeexceed 5 F. 



