We addressed thiamine status in 3 species of fish that are frequently raised in hatchery operations. We monitored thiamine deficiency in lake trout population from different spawning grounds of L. Michigan, and walleye and yellow perch from L. Erie. Specifically, we examined if survival of alevins of lake trout was compromised due to early mortality syndrome (EMS). The assumption was that different diets may lead to differences in severity of EMS between different stocks. Batches of lake trout egg were collected and fertilized individually with the sperm of several males. The eggs, eyed embryos and newly-hatched alevins were sampled to examine thiamine utilization during embryonic development. Progenies of females with low (< 0.73 nmol/g) and high (> 0.85 nmol/g) levels of thiamine were chosen for histological studies. The obtained results revealed that total thiamine levels in the body and yolk of eyed embryos and alevins at hatching were influenced by the thiamine levels in unfertilized eggs and decreased during embryogenesis (to 51% in eyed embryos and 28% in newly-hatched alevins in comparison to unfertilized eggs). However, the survival of lake trout until hatching stage did not correlate with thiamine levels. No pathological changes were observed during the hatching stage in the brain, olfactory lobe, retina or liver in the embryos regardless of thiamine concentrations. We conclude that an enhanced thiamine requirement for fast muscle mass growth near the swim-up stage is responsible for the overt and histopathological signs of EMS. The current study confirms earlier findings that lake trout suffering from EMS can be successfully treated by immersion in thiamine solution as late as at the swim-up stage.
We examined thiamine concentrations in walleye eggs during the 2004-2008 spawning seasons these were relatively high (4.8-7.8 nmol/g) considering the dominance of gizzard shad in their diet. Overall, there was a positive correlation between thiamine concentrations in eggs and survival of pigmented eyed embryos. This indicates that thiamine deposited in the yolk will be further utilized for accelerated muscle growth and clinical signs of deficiency might be exhibited after hatching. Yellow perch eggs were analyzed during the 2009 and 2010 spawning seasons and thiamine concentrations were higher in these (2.7 nmol/g) than in affected salmonids (>0.8 nmol/g). However, when eggs were immersed in thiamine solution after fertilization, the survival of embryos increased significantly. We conclude that thiamine deficiency might be further exacerbated during yolk absorption and the transition to exogenous feeding.