Effects of feeding high dietary thiaminase to sub-adult Atlantic salmon from three populations

Salmonids consuming high thiaminase-containing prey fishes can develop debilitating thiamine deficiencies. Historically, salmonids within the Laurentian Great Lakes consumed low thiaminase-containing prey fishes. Currently, however, salmonids are consuming introduced high thiaminase-containing prey fishes, which may be an impediment to the persistence of native species. Here, we examined the effects of feeding high thiaminase on sub-adult (two-year-old) Atlantic salmon (Salmo salar) from three populations (LaHave, Sebago, and Saint-Jean) that are being used for reintroduction into Lake Ontario. The thiaminase diet, mimicking the current high thiaminase concentrations of prey fishes, was produced by mixing natural bacterial thiaminase into prepared feed. After 6 months of feeding fish the thiaminase diet, we found significant drops in thiamine in red blood cells, white muscle, and liver tissues in all three populations as compared to fish fed a control diet. Additionally for liver tissue, we found a higher reduction in thiamine for the LaHave population relative to the Sebago and Saint-Jean populations. Although the salmon fed the thiaminase diet had no change in survival or growth after 8 months, the salmon had lower swimming performance than fish fed a control diet. There were also trends for lower body condition, a less streamlined body shape, and less yellow body pigmentation when fed the thiaminase diet. The changes in these latter traits may indicate the onset of a thiamine deficiency and could negatively impact Atlantic salmon survival in the lake.