272 BULLETIN OP THE BUREAU OP FISHERIES. 



lesions on the tail and died a few hours later. The remaining control died the next 

 day with a large lesion on the side of the head. In short, there was a loss of 31 % per 

 cent among the treated fish and 100 per cent among the controls. Four of the five fish 

 which died among the treated lot were in all probability killed by the direct effects of 

 the copper sulphate. A large number of experiments have shown that fish when 

 weakened in any way, as by handling or being kept in water deficient in oxygen, are 

 much more susceptible to the injurious effects of the treatment than perfectly normal 

 fish and are often killed by solutions which will not appreciably injure fish in good con- 

 dition. It is this fact which has made it impossible to devise a treatment which will 

 be successful under all conditions. Of course it is evident that the fish which are so 

 weakened as to be injured by the treatment are the very ones which are most liable 

 to contract the disease if not treated. 



It has not been practicable to conduct many experiments so completely under 

 control as this one, but we have in a number of instances successfully checked by this 

 treatment an outbreak of the disease among fish which were being kept in aquaria for 

 other purposes. Another test of the treatment under somewhat different conditions 

 is of considerable interest: On July 20, 1919, in connection with a series of feeding 

 experiments which were being carried on at the Fairport station, a number of 3-year-old 

 buffalofish were seined from the pond in which they had been confined for some 

 time and distributed among four different ponds. This necessitated handling the fish 

 rather roughly and transferring them some distance in a galvanized tank. To make 

 matters worse it was a very hot day and under ordinary circumstances there would 

 undoubtedly have been considerable loss, especially since many of the fish were badly 

 rubbed during the transfer. Before being liberated in the ponds all the fish were 

 treated for 20 minutes with a 1 to 30,000 solution of copper sulphate. Of the 551 fish 

 treated only 4 died as a result of the transfer, and none of these showed any evidence of 

 the disease. It is unfortunate that in this case it was not practicable to keep any 

 controls for comparison with the treated fish. 



While the treatment described above has been very successful it has the great 

 disadvantage of requiring considerable time, and this is a serious objection where many 

 fish are to be treated. During the summer of 1919 extensive experiments were carried 

 on with a view to shortening the treatment. As a result a rapid treatment has been 

 devised which is believed to be even more effective than the longer treatment previously 

 in use. Briefly, the new method consists in treating the fish with a 1 to 1,000 solution 

 of copper sulphate for one to two minutes. This treatment is so great an improvement 

 on the earlier treatment with a 1 to 30,000 solution that in our later experiments we 

 entirely discarded the latter. 



When the fish are in good condition they can be placed in the 1 to 1,000 solution 

 for two minutes without injury, but if they have been previously weakened in any way 

 they should not be exposed to the solution for more than one minute. Such hardy 

 fishes as the black bass, sunfishes, and bullheads can be safely left in the solution for 

 three minutes if in good condition. In some cases it is advisable to repeat the treatment 

 after 12 to 24 hours. 



A number of experiments with the rapid treatment were carried out during the latter 

 part of the summer of 1919, but it will suffice to describe a few representative experiments. 



