Mercury, selenium, and fatty acids in the axial muscle of largemouth bass: evaluating the influence of seasonal and sexual changes in fish condition and reproductive status

Fish muscle mercury concentration and bioaccumulation fluctuate year-round - Insights from cyprinid and percid fishes in a humic boreal lake

Boreal lakes demonstrate pronounced seasonality, where the warm open-water season and subsequent cold and ice-covered season dominate natural cycles. While fish muscle total mercury concentration (mg/kg) [THg] is well documented in open-water summer months, there is limited knowledge on the ice-covered winter and spring mercury dynamics in fish from various foraging and thermal guilds. This year-round study tested how seasonality influences [THg] and its bioaccumulation in three percids, perch (Perca fluviatilis), pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernua), and three cyprinids, roach (Rutilus rutilus), bleak (Alburnus alburnus), and bream (Abramis brama) in deep boreal mesotrophic Lake Pääjärvi, southern Finland. Fish were sampled and [THg] was quantified in the dorsal muscle during four seasons in this humic lake. Bioaccumulation regression slopes (mean ± STD, 0.039 ± 0.030, range 0.013-0.114) between [THg] and fish length were steepest during and after spawning and shallowest during autumn and winter for all species. Fish [THg] was significantly higher in the winter-spring than summer-autumn in all percids, however, not in cyprinids. The lowest [THg] was observed in summer and autumn, likely due to recovery from spring spawning, somatic growth and lipid accumulation. Fish [THg] was best described by multiple regression models (R2adj: 52-76%) which included total length and varying combinations of seasonally changing environmental (water temperature, total carbon, total nitrogen, and oxygen saturation) and biotic factors (gonadosomatic index, and sex) in all species. The seasonal variation in [THg] and bioaccumulation slopes across multiple species suggests a need for standardized sampling seasons in long-term monitoring to avoid any seasonality bias. From the fisheries and fish consumption perspective in seasonally ice-covered lakes, monitoring of both winter-spring and summer-autumn would improve knowledge of [THg] variation in fish muscle.

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

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.