Effects of Microcystin on Juvenile Lost River Suckers

Lack of recruitment into Lost River and shortnose sucker spawning populations in Upper Klamath Lake is a primary factor preventing the recovery of these endangered species.  Although both species are known to successfully spawn, almost no juvenile suckers survive past their first two years of life.  The coincidence of this disappearance of juvenile suckers with episodic decay of massive blooms of cyanobacteria, widespread hypoxia, and high concentrations of cyanotoxins, points to a factor or combination of factors associated with degraded water quality.  Furthermore, the disappearance of juvenile suckers from trap net catches tends to occur with a 2-3 week lag from when peak concentrations of microcystin are found in the lake, suggesting that ingestion of microcystin through the food chain could be a factor in juvenile sucker mortality.  Short term feeding trials of microcystin at a variety of concentrations similar to concentrations found in Upper Klamath Lake did not cause mortality or major tissue damage even though microcystin was recovered from a variety of tissues including the guts, muscle, and head.  Tissues were further examined for histopathological changes consistent with those observed in other fish species following sublethal exposure to microcystin.