OPERATING THE HATCHERY 



viously been filled with water to 

 the calibration mark. The inner 

 compartment is then placed in the 

 trough which contains the fish to 

 be treated, and a convenient num- 

 ber of fish from the trough are 

 placed in it by means of a scap 

 net. The compartment is then re- 

 moved to the dipping box and the 

 fish immersed in the disinfectant. 

 After the required time for the dip 

 has elapsed, the inner compartment 

 is carefully lifted from the dip- 

 ping box and innnersed in the 

 trough to which the treated fish 

 are being transferred. By slowly 

 lifting the "upstream" end of the 

 inner compartment, the fish slip 

 out into the trough. The solution 

 in the dipping box should be aer- 

 ated constantly and renewed fre- 

 quently. Differences in water tem- 

 perature between the infected 

 trough, the dipping box, and the 

 treated trough should at no time 

 exceed 5° F. 



For treatment by dipping as 

 used most frequently, the formula 

 for external parasites is glacial 

 acetic acid, 1 part dissolved in 500 

 parts of water; for gill disease, it 

 is 1 part of copper sulfate (blue 

 stone) in 2,000 parts water; and 

 for various external infections with 

 animal ])arasites and fungi, it is a 

 o-percent solution of salt. Fish 

 are usually dipped for 1 minute in 

 acetic acid and copper sulfate, and 

 in salt for several minutes until 

 the weakest fish begin to turn over. 



Prolonged treatment 



Prolonged treatments are based 

 on the theory that long exposure to 



a dilute solution of disinfectant is 

 more effective and less toxic than 

 is the shorter, more-concentrated 

 hand dip. Furthermore, prolonged 

 treatment may be applied without 

 liandling the fish, a factor which is 

 not serious if the fish are carefully 

 treated from troughs, but may be- 

 come very serious when the fish are 

 in ponds or pools where a seine 

 must be used and a large number of 

 fish is involved. 



Prolonged treatment originally 

 consisted of adding to the inflow- 

 ing water a sufficient amount of 

 dissolved disinfectant at a uniform 

 rate to maintain a constant concen- 

 tration of disinfectant over a defi- 

 nite period of time, usually 1 hour. 

 This method of treating the inflow- 

 ing water is subject to an inherent 

 inaccuracy due to the diluting influ- 

 ence of the residual water in the 

 pond at the time treatment is 

 started. Although not serious in 

 the case of troughs or small race- 

 ways which may be drained prac- 

 tically to dryness and which fill rap- 

 idly, the inaccuracy becomes pro- 

 gressively greater as the size of the 

 body of water to be treated is 

 increased. 



For treatment of fish in larger 

 water areas, such as circular pools, 

 raceways, or ponds, the prolonged 

 treatments are identical in princi- 

 ple to salting, page 51. The volume 

 of water in the pool (capacity of 

 the pool) to be treated must be 

 known ; then the required quantity 

 of the disinfectant is weighed, or 

 measured by volume if it is a liquid, 

 and dissolved in a small quantity of 



54 



