Effects of thiamine on reproduction of Atlantic salmon and a new hypothesis for their extirpation in Lake Ontario

Previous researchers demonstrated that a mortality in fry (called Cayuga sy ndrome) of Atlantic salmon Salmo salar from Cayuga Lake (New York) was asso ciated with low levels of thiamine. They reduced the mortality of fry by ba thing or injecting fry with thiamine. We injected four to six gravid female Atlantic salmon with either physiological saline (PS) or PS plus thiamine (7 mg/kg weight) 14-23 d before eggs were stripped, fertilized, and incubat ed in individual lots. Chemical analyses showed that eggs from control and treated salmon contained 1.1 and 1.6 nmol thiamine/g, respectively. Thiamin e injections had no significant effect on the percentage of eggs that hatch ed. Between 700 and 800 Celius degree-days postfertilization, control fry ( saline) showed signs of Cayuga syndrome and a 45% incidence of mortality; i n contrast, mortality was only 1.9% for fry that received thiamine. By 1,07 8 degree-days postfertilization, mean mortality of control fry was 98.6%, w hereas that for thiamine-injected salmon was 2.1%. This study showed that t hiamine injections of prespawning female salmon from Cayuga Lake increased thiamine content of their eggs and prevented the Cayuga syndrome and subseq uent mortality of fry. Historically, overfishing, pollution, and building o f dams and barriers to spawning migration were suggested as possible causes of the decline of the Atlantic salmon in Lake Ontario and Cayuga Lake. Bas ed on our findings and other reports, we suggest another possible contribut ing cause of the extirpation of landlocked Atlantic salmon in Lake Ontario and some other inland waters of New York: the entrance of alewives Alosa ps eudoharengus containing thiaminase, which induced thiamine deficiency in eg gs and increased mortality in fry of the predatory salmon.