The U.S. Fish and Wildlife Service is looking into whether a previously unexplored vitamin deficiency could play a role in the decline of sucker species in the Klamath Basin.
Thiamine, also known as vitamin B1, is essential for all vertebrates. It helps enzymes break down sugars, produce energy and create genetic material. In fish, it plays a significant role in early growth and development.
Donald Tillitt, an environmental toxicologist with the U.S. Geological Survey who has been studying the role of thiamine in aquatic ecosystems for roughly 30 years, said the vitamin is produced by plants and bacteria at the base of the food web — organisms at higher trophic levels can’t synthesize the molecule themselves. When there’s a lack of the crucial vitamin in an ecosystem, it’s almost always a problem with the food web.
“When there are alterations in the food web...that can change not only the type of food items but also the quality of the food,” Tillitt said.
If an ecosystem becomes disrupted, the nutrients passed through its food web can change and result in thiamine deficiency complex (TDC) in a species. Tillitt said that could happen through lower production of the vitamin at the base level or a change in how existing thiamine passes from one organism to another. The latter has been studied more extensively in various locations.
Some organisms produce an enzyme called thiaminase, which breaks down thiamine and renders it unusable. When they’re alive, the enzyme remains trapped in a cell vesicle, but when another organism consumes and digests them, the thiaminase releases and can degrade the predator’s thiamine level.
“We don’t even know why those fish produce the thiaminase,” Tillitt said. “We’ve got some ideas, but we really don’t know what the purpose of that thiaminase is.”
The Great Lakes, for example, saw adequate spawning but low recruitment in lake trout for years. Scientists discovered that alewives, an invasive species that became a significant food source for the trout, contained high levels of thiaminase.
Trout that ate alewives saw their thiamine levels drop significantly over several months and produced eggs that were thiamine-deficient. Those eggs were able to hatch, but fry were lacking levels of thiamine sufficient to develop normally. They weren’t able to successfully swim up into the water column to feed on organisms that would’ve boosted their thiamine levels, and they subsequently died.
“They didn’t have a chance,” Tillitt said. “They have neurological problems — you can see they have sort of erratic behavior. They swim in circles. Sometimes they can’t keep themselves upright in the water column.”
Local researchers saw parallels between the situation in the Great Lakes and the situation in Upper Klamath Basin: Adult C’waam and Koptu (Lost River and shortnose suckers) successfully reproduce year after year, but almost none of their offspring live long enough to reach sexual maturity. The issue has been going on for long enough to render the fish endangered. And the aquatic ecosystem has been modified significantly from its original state, from water quality to species composition.
“There were some similarities to the story of lake trout,” Tillitt said.
Additionally, as outlined by University of Washington environmental engineering professor Michael Brett at March’s Sucker Symposium, there’s a theory that blue-green algae are associated with thiamine deficiency.
Species of the cyanobacteria genus Aphanizomenon present in the brackish waters of the Baltic Sea (cousins of the AFA monoculture that blooms yearly in Upper Klamath Lake) produce thiamine, but research has shown that the zooplankton consuming them have low thiamine. Some cyanobacteria are known to produce thiaminase, too, which could potentially be why the vitamin doesn’t percolate throughout the food web.
“There seems to be this kind of trophic bottleneck,” Brett said.
The similarities between the Klamath Basin and ecosystems that are known to deal with thiamine deficiency led Christie Nichols, science coordinator for the Fish and Aquatic Conservation Program in the Klamath Falls FWS office, to seek Tillitt’s help in jumpstarting an exploration of the vitamin’s potential role here.
“The Service is just beginning to explore this new line of investigation to see if this vitamin deficiency, seen in other systems, might also be an issue in the Klamath Basin,” Nichols said.
Biologists collected a small number of egg samples from female suckers last year and sent them to Tillitt’s lab. Compared to normal concentrations observed in other fish species, Nichols said the thiamine levels found in sucker eggs were “very low,” though the sample size was too small to make a generalization about the entire population. Still, the preliminary results were notable enough to pursue this line of research.
“I think it’s a good idea to be investigating this potential as a stressor,” Tillitt said. “Right now, we don’t know it all.”
Nichols said the plan for this year is to collect tissue samples from all sucker life stages to paint a better picture of “normal” thiamine levels in suckers, which will give them something to compare future egg samples to. She emphasized that this research is in its infancy, and no definitive claims can be made about thiamine deficiency in the Klamath Basin at this point.
“Hopefully, the 2021 sampling, which includes a more accurate lab analysis, will help us understand if this is a persistent problem,” she said.
If thiamine deficiency turns out to be a factor in the lack of sucker recruitment in the Basin, managers could take concrete action to mitigate it. On the Sacramento River, for example, some endangered salmon runs salmon were found to suffer from thiamine deficiency — so much so that simply placing hatchery fry in vitamin-rich water made them act normally.
Tillitt said while thiamine deficiency can be a relatively simple thing to fix in a controlled setting like a hatchery, it’s still a symptom of more systemic ecological woes that aren’t easily improved. The current hypothesis regarding suckers is that a host of poor conditions — from low dissolved oxygen to temperature to pH — chip away at fish health and that there’s not necessarily one silver bullet that can save them from extinction.
“It’s a dysfunctional ecosystem that’s going on if there is this thiamine deficiency occurring,” Tillitt said. “That’s a longer, bigger, much more complex problem.”