Adult steelhead trout returning to the Salmon River from Lake Ontario are showing signs of stress and higher mortality rates because of a vitamin deficiency, the New York Department of Environmental Conservation (DEC) announced on Wednesday, Jan. 7.

DEC staff have called on experts in fish health from other agencies as well as the academia to figure out the root of the disorder and have so far been told that fish pathogens are not to blame. What is clear, though, is that the steelhead population is suffering from a severe thiamine deficiency and this is likely to be a contributing factor to higher mortality rates.

"Lake Ontario steelhead are an important component of Lake Ontario's sport fishery and DEC is deeply concerned about reports of steelhead stress and mortality in the Salmon River and other Lake Ontario tributaries," said Joe Martens, DEC Commissioner, adding the agency will continue to work with stakeholders, Cornell University and other federal agencies to get to the bottom of the situation and come up with a plan to reinvigorate the steelhead population in Salmon River.

Reports of erratic steelhead behavior in Salmon River were received by the DEC starting mid-November, but now more are being observed in other tributaries of Lake Ontario. As an important part of sport fishery in the area, steelhead are valued to be responsible for more than $112 million in angler expenses in state every year.

Fish predators like steelhead primarily feed on alewife, an invasive type of bait fish found in the Great Lakes. As alewife contain thiaminase, an enzyme that breaks down thiamine, it leads to thiamine deficiency in the fish that eat it. Aside from the death of an adult fish, thiamine deficiency wreaks havoc in a fish population by affecting egg quality, which also determines whether or not it will hatch and if a newly hatched fish will survive and grow to become an adult.

It's not unheard of for top predator fish to suffer thiamine deficiencies, but the level at which the vitamin is lacking in steelhead this year is very severe. For now, the DEC is addressing thiamine deficiency in the steelhead population by injecting steelhead adults with the vitamin. For the agency to do that, the fish must first make its way up the river and into the Salmon River Hatchery's holding facilities.

Aside from getting thiamine injections, fish held in the hatchery's outdoor raceway will also be fed fortified diets to improve chances of successful egg collecting in 2015.