Microcystin accumulation in Sportfish from an agricultural reservoir differs among feeding guild, tissue type, and time of sampling.

• Cyanotoxins can accumulate in fish tissues through trophic transfer. • Microcystin concentrations in bluegill were higher than in largemouth bass. • Microcystin was highest in fish livers, followed by kidneys, and then muscles. • Time of year was the greatest predictor of microcystin in fish tissues. • Low but frequent water microcystin occurrences can result in accumulation in fish. Cyanobacterial blooms sometimes create secondary metabolites that can be transferred between trophic levels and accumulate in fish, but little is known about what time of year fish are most susceptible. Here, we examine microcystin in the muscle, liver, and kidney of bluegill and largemouth bass from an agricultural reservoir over 12 months. We identify which fish characteristics and water parameters best explain microcystin accumulation in fish tissues. Microcystin in bluegill was significantly higher than largemouth bass. In both species, microcystin was highest in livers (bluegill mean = 57.6 ng g −1, largemouth bass mean = 71.8 ng g −1 wet weight [ww]), then kidneys (bluegill mean = 27.1, largemouth bass mean = 22.7 ng g −1 ww), followed by muscles (bluegill mean = 7.6, largemouth bass mean = 5.7 ng g −1 ww). Adult bluegill feed on benthic macroinvertebrates and zooplankton, which may explain their higher microcystin concentrations compared to largemouth bass, which are primarily piscivorous. Harvest date emerged as the best predictor of microcystin in muscles and kidneys, with the highest concentrations occurring in April. Microcystin in water also emerged as a significant predictor, albeit much lower than harvest date, suggesting that low but persistent microcystin concentrations in water may result in accumulation of this cyanotoxin in fish. This study is the first to examine microcystin in fish from the North American Great Plains and one of only 5 studies that investigate microcystin in bluegill and largemouth bass. Additional investigation into the relationship between cyanobacteria and fish health is warranted, especially during spring when fish microcystin concentrations were highest. [ABSTRACT FROM AUTHOR]