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Ladago, Bret J.

Rubenstein School of Environment and Natural Resources

2014

M.S.

Thiamine (vitamin B₁) deficiency in salmonids has been linked to adult consumption of thiaminase-containing forage fish, particularly alewife. In the Great Lakes, the introduction of alewife in the early 20th century is thought to contribute to recruitment failure of salmonids; hatchery fry with less than 4 nmol/g thiamine show deficiency symptoms that can lead to high mortality. The recent invasion of alewife in Lake Champlain in 2003 offered the opportunity to track changes in salmonid thiamine. By 2009, symptoms of thiamine deficiency were prevalent in local hatcheries, prompting routine treatment of eggs and fry with thiamine. Thiamine levels in feral lake trout and Atlantic salmon eggs measured in 2004, prior to alewife expansion, were high (average 11.2 ± 3.4 nmol/g). Thiamine concentrations in lake trout dropped to 5.1 ± 3.9 nmol/g in 2007 and have averaged 5.31 ± 4.8 nmol/g since then.
Thiamine levels in Atlantic salmon dropped to 3.7 ± 1.9 nmol/g in 2007 and remain low. Despite low egg thiamine, emergence of wild lake trout fry in Lake Champlain is high. Early feeding in salmonid fry has not been well studied; fry may enrich their thiamine by consuming zooplankton. Stomach contents of 364 wild-caught lake trout fry were examined. Roughly 20% of early sac fry had food in their stomachs, and by yolk sac adsorption 98% of fry had begun feeding. The presence of early feeding suggests the possibility that thiamine deficiciency may be mitigated in wild lake trout fry.