THE PUBLIC AQUARIUM 323 



in hatching whitefish "with chlorinated water from the Bay City 

 system. The Bureau of Fisheries' substation at Alpena, Mich., 

 likewise suffered egg losses (seriously restricting its usefulness at 

 certain periods) by using a chlorinated water supply. Discontin- 

 uance of the practice in 1922 was followed by the restoration of 

 normal conditions at this hatchery. The Bureau of Fisheries has 

 received numerous inquiries that show that similar troubles are en- 

 countered in many places. 



That the mortalities are due to chlorine is incontestable. The 

 experimental evidence, the correspondence of the inception and dis- 

 appearance of the trouble to periods of chlorination and nonchlorina- 

 tion, and the augmenting of losses contemporary with known chlorine 

 surges in the water, all render it unnecessary to elaborate proof. 

 The purpose of this paper is to indicate remedial measures. 



CHARACTERISTICS OF CHLORINE POISONING 



A multitude of conflicting factors renders it impossible to oJffer 

 a description of a typical case of chlorine poisoning. The species 

 and age of the eggs or fish, the filtration or nonfiltration and organic 

 content of the water, the probabilities of sudden heavy increases in 

 the residual chlorine content, temperature, etc., are conditions that 

 must be known to permit any prophecy as to what reactions may 

 occur in a given case. 



While the experience at the central station has been that the eggs 

 of whitefish and salmonids are largely unaffected until the hatching 

 stage, at the hatcheries cited above it is reported that whitefish 

 and lake-trout eggs were injured during incubation. In all cases it is 

 noted that the most serious inroads are apparent following hatching, 

 when an acceleration of the physiological activity of the fry occurs. 

 At this stage the latter are highly susceptible. 



In comparison of the fingerlings and the older stages it is ob- 

 served that the former are more vulnerable to chlorine poisoning. 

 Rainbow-trout fingerlings Xo. 1 and yearlings were shipped to the 

 central aquarium at the same time from one of the hatcheries; the 

 fingerlings commenced to show mortality immediately, and, although 

 there were more of them, they failed to survive as long as the older 

 individuals. The latter succumbed only after an interval over the 

 week end, when presumably there was a marked increase in the 

 residual chlorine, and one of the six survived this increase. Attempts 

 to hold brook trout and salmon have revealed a comparable condition. 



The comparative susceptibility of different species seems to be 

 roughly correlated Avith their tolerance of other poisons and of 

 adverse environmental conditions. Goldfish and other cyprinids, 

 while not unaffected, maintain themselves fairly well under ordinary 

 dosage; the sunfishes and basses show considerable resistance as 

 well. The trout, salmon, and whitefish will be the first victims 

 when chlorine makes its appearance in the water supply. 



A variation in susceptibility among individuals of the same species 

 exists, as would be expected. Among the more resistant forms, as 

 the goldfish, a few will succumb early: and it will be found that these 

 individuals are marked by poor condition, parasitic infections, etc. 



