Thiamine availability and uptake in lake trout (Salvelinus namaycush) eggs and embryos: contrasting natural and artificial environments

Thiamine Deficiency Complex (TDC) is a reproductive disorder that affects recruitment of salmonine populations globally. Symptoms include behavioural and neurological abnormalities and high offspring mortality. TDC has typically been studied in hatcheries that rear embryos obtained from wild populations, and symptoms are mitigated by thiamine treatment. Few studies have evaluated TDC in wild embryos, largely due to logistical challenges. Here, we evaluated whether embryos can acquire thiamine from natural sources (i.e., biotic breakdown products and diet) during development. Lake trout ( Salvelinus namaycush ) gametes were obtained from feral adults in Lake Champlain and eggs were grouped by family with paired fertilization and rearing under natural (Lake Champlain) and artificial (laboratory) conditions. Average total thiamine concentrations were greater among eggs fertilized using lake water and embryos reared in the lake compared to eggs fertilized using laboratory water and those reared in the lake. Lake-reared embryos also experienced significant increases in thiamine concentrations at hatch and approximately five weeks later compared to unfertilized and fertilized eggs, and compared to laboratory-reared embryos. Laboratory-reared embryos experienced minimal increases in thiamine concentrations throughout development, particularly compared to increases observed among lake-reared embryos. Water samples collected from the lab and lake sites contained measurable concentrations of thiamine precursors and byproducts, which may serve as sources of thiamine for developing embryos. These results demonstrate that lake trout eggs and embryos can acquire thiamine from natural sources during development, which may mitigate TDC.