Egg thiamine threshold for reproduction of rainbow trout

Rainbow trout (Oncorhynchus mykiss) eggs obtained from Cayuga Lake (New York) occasionally produce thiamine-deficient fry that manifest general weakness, loss of equilibrium and increased mortality that can be prevented by immersing fry in water with added thiamine. To examine the nature and extent of this deficiency, we captured pre-spawning male and female rainbow trout in Cayuga Inlet of which five female trout were injected with thiamine (50 mg/kg) and ten were not. All trout were held in the laboratory until spawned. Eggs were incubated as separate lots. Analyses of eggs showed that injections significantly increased mean concentration (±Std. Dev.) of thiamine from 2.45±1.77 to 4.53±1.10 nmol/g. To determine whether mortality of fry at 470 centigrade degree-days post-hatch was related to thiamine deficiency, newly-hatched fry from each female were immersed in either plain water or water containing 1,000 mg/L added thiamine for 24 hr (with aeration) to detect mortality that was non-responsive to thiamine. When non-responsive egg lots were omitted, our estimated minimum threshold concentration of egg thiamine for fry survival was between 1.6 and 1.8 nmol/g  compared to 1.6 and 2.15 nmol/g when all values were used. Therefore, most rainbow trout in Cayuga Lake produced eggs adequate in thiamine.