Early Feeding by Lake Trout Fry

The restoration of Lake Trout Salvelinus namaycush in the Great Lakes and Lake Champlain has been challenging due to the bottlenecks in recruitment that occur mostly during early life stages. Among possible sources of fry mortality (e.g., predation, starvation, and disease), the least is known about the diet and starvation risk of pre-emergent fry. The first feedings by fry are generally assumed to be delayed until close to the absorption of the yolk sac and the emergence of the fry. The stomach contents of 374 wild-caught Lake Trout fry from Lake Champlain were examined from hatching to the exogenous feeding stage to identify the earliest occurrence of feeding relative to yolk sac absorption and to describe the diet. Within 2 weeks of hatching, 19% of fry had food in their stomachs. At 4–6 weeks and after yolk sac absorption, 98% of fry began feeding. Diet was primarily comprised of Bosmina as well as calanoid and cyclopoid copepods, and fry contained up to 215 items per stomach. Our finding that fry began feeding within 2 weeks of hatching (prior to yolk sac absorption) is relevant to current concerns that Lake Trout fry mortality in the Great Lakes is caused by thiamine deficiency syndrome: wild Lake Trout fry may be able to mitigate thiamine deficiency with early feeding on thiamine-rich zooplankton.