Thiamine and early mortality syndrome in lake trout.
Reproductive success and vitamin B1 (thiamine pyrophosphate, thiamine monophosphate, and free thiamine) concentrations were assessed in feral female lake trout, Salvelinus namaycush, from Lake Ontario and Lake Manitou. Fertilization success, survival to hatch, incidence of blue-sac disease, other anomalies, and lake trout early mortality syndrome (EMS) were monitored. Fertilization and hatching success were high, whereas mortality from blue-sac disease and other anomalies was low in egg batches from both lakes. There was no mortality from EMS in families from Lake Manitou. However, EMS occurred after hatching in the offspring of 48% of the females collected from Lake Ontario. Thiamine was estimated in the liver, red blood cells (RBC), eggs and developing embryos. Relative to fish collected in reference lakes, females in Lake Ontario had reduced hepatic, RBC and egg thiamine concentrations. Although more extensive investigation of thiamine balance is required, it may be possible to use red blood cell thiamine pyrophosphate as a predictive index for EMS susceptibility in offspring. Total thiamine levels in developing embryos declined by 50% between fertilization and swim-up. Free thiamine reserves declined most rapidly, whereas levels of thiamine pyrophosphate increased between the eyed embryo and hatch stages. A high proportion (67%) of lake trout families in which the initial egg free thiamine reserves or embryonic concentrations of thiamine pyrophosphate levels were <0.8 nmol/g exhibited EMS. Below this threshold (0.8 nmol/g), the occurrence of EMS was variable (0-100%) and only weakly related to free thiamine concentrations (r2 = 0.32, P=0.014); this implies the possibility of additional interactions with other factors.