4 U. S. BUREAU OF FISHERIES. 



usual method of reproduction, though the parasite may undergo 

 one or two stages of division while embedded on the host or as a 

 free-swimming form after leaving the fish. The rapidity with 

 which the parasite goes through its life cycle depends on the tem- 

 perature of the water, the kind of fish infected, the region in which 

 it becomes embedded, and the metabolic activity of its host. 



Under general conditions the parasite will remain on the fish for 

 five or six days in warm water of 65° F. or higher, and, on the other 

 hand, in water of 35 to 40° F. it may not leave the fish for a month 

 or more. The parasite is not killed when it leaves the fish in water 

 at a freezing temperature but continues to develop and multiply 

 very slowly and is ready to reinfect the fish in three or four weeks. 

 The logical time to begin treatment is when the first symptoms of 

 the disease appear, and the whole fight in controlling the disease 

 should be directed against reinfection. 



TREATMENT AND CONTROL OF THE DISEASE. 



There are two general methods for treating the disease — first, by 

 killing the parasites while they are attached to the fish, and, second, 

 by destroying them after they leave the fish and are free-swimming 

 in the water. The first general method can be used to hold the 

 disease in check but will not completely wipe it out. 



The external application of various chemicals in solution is help- 

 ful to a certain degree, as it kills and removes those parasites that 

 are about to leave the fish as well as the smallest forms that have 

 burrowed into the mucous coating. Past experiments with chemi- 

 cals, such as copper sulphate, formaldehyde, sodium bicarbonate, 

 sodium chloride, and others, have been successful in killing the para- 

 site but have so weakened the fish that they either die or soon develop 

 fungus growths and bacterial disease, which eventually prove fatal. 

 For external treatment of parasitized fish the use of aluminum sul- 

 phate (alum sulphate) in solution is most satisfactory. The slime and 

 mucus covering the fish become congealed and are soon shaken off, 

 and the healing effect of the alum leaves the skin in a less weakened 

 condition than do the effects of other chemicals. The fish may 

 either be dipped or rubbed with the alum solution. In dipping a 



5 per cent solution is used and the fish are allowed to remain in it 

 for one minute. For mixing a large quantity of the solution use 

 6^ ounces of alum sulphate to 1 gallon of water, store in a glass, 

 wood, or porcelain container and change every five days. For 

 rubbing or brushing the fish a 3 per cent solution is used, or 4 ounces 

 of alum sulphate to 1 gallon of water. The fish are laid in a shallow 

 pan with about half an inch of the solution in the bottom of it, and 

 the affected parts are gently rubbed with saturated cheesecloth or 

 a brush. These chemical applications have been used successfully 

 on carp, catfish, bass, sunfish, goldfish, Fundulus, bream, and trout, 

 but were only helpful as a means of holding the disease in check by 

 killing those parasites that were about to leave the fish. Alum sul- 

 phate has also given excellent results in the treatment of Sapro- 

 legnia when applied in a 3 per cent solution to the diseased parts 

 of the fish. 



The second general tnethod for combating the parasite is the most 

 practical and should be put into effect in every possible case. It 



