DISEASE CONTROL 



external parasites is evidenced in 

 the fish refusing to eat, scratching 

 themselves, or assuming a character- 

 istic bluish-gray sheen. Fungus is 

 an excellent indicator of trouble, but 

 it usually does not appear until after 

 the telltale rise in the daily losses — 

 which is the surest proof that 

 trouble is present. 



Immediately upon any suspicion 

 of trouble and always in the event 

 of increasing losses, the fish should 

 be carefully examined for gross 

 lesions, and all possible extraordi- 

 nary factors, such as bad food, silt, 

 and sudden fluctuations in water 

 temperature, should be checked. If 

 none of these is involved, the fish 

 should be examined for parasites 

 and microscopic lesions. There are 

 many diseases of fishes w^hich are 

 diiRcult to diagnose or treat, or both. 



When in doubt as to the cause of 

 losses, the fish culturist should seek 

 the advice of a State fishery biolo- 

 gist. Whenever it is necessary to 

 send the diseased fish to a diagnos- 

 tic laboratory, the specimens se- 

 lected should be fish with the most 

 typical symptoms or signs of the 

 disease, but still living. It is very 

 difficult and often impossible to 

 diagnose a disease from a dead fish. 

 If living fish cannot be brought to 

 the laboratory, live fish with typical 

 symptoms should be placed in a jar 

 containing 1 part of commercial 

 formalin diluted with 3 to 4 parts 

 of w^ater. A letter should accom- 

 pany the specimen, giving as de- 

 tailed information as possible re- 

 garding the progress of the disease, 

 percentage and rate of losses, and a 



detailed description of the condi- 

 tions existing in the pond or tank, 

 such as turbidity, presence of vege- 

 tation, waterbloom, water tempera- 

 ture, and any treatment of the pond 

 or fishes. The more accurate the de- 

 scription of the symptoms and con- 

 ditions that is given the more likely 

 it is that the biologist will be able to 

 determine the cause of trouble and 

 recommend treatment. 



METHODS OF TREATMENT 



Regardless of the concentration 

 of the disinfectant used, the tech- 

 nique of application influences the 

 success of any treatment to no small 

 degree. It might, therefore, be ad- 

 vantageous to briefly outline the 

 various methods of treatment in 

 common use and the recommended 

 techniques. 



Salting 



Salting is good trough treatment, 

 but it will not cure everything. In 

 troughs, it is extremely simple to 

 apply, is reasonably effective 

 against external protozoan para- 

 sites, is an excellent tonic for the 

 fish, and its application demands 

 the least accuracy of any known 

 form of treatment. 



There are many w ays to treat fish 

 by salting, and some methods are 

 better than others. In the method 

 recommended here, fish are treated 

 v/ith a known concentration of com- 

 mon salt. Salt should be dissolved 

 in water in a quantity to give a 3- 

 percent concentration when added 

 to the water in which the fish will 



51 



