title: Effects of dietary methylmercury on juvenile Sacramento blackfish bioenergetics.
abstract: Although much is known about the biogeochemical cycling of mercury in the environment, relatively little is known about methylmercury (MeHg) bioaccumulation in fishes and how chronic sub-lethal exposures affect their functioning. Several species of fish in Clear Lake, California have high MeHg tissue levels, including Sacramento blackfish, Orthodon microlepidotus, a large native cyprinid that is fished commercially. We fed juvenile blackfish one of four diets containing MeHg (0.21 mg/kg control; 0.52 mg/kg low; 22.2 mg/kg medium; and 55.5 mg/kg high treatments) for 70 days. There were no statistical differences (P > 0.05) in food consumption among the treatment groups. By 35 days the high treatment group had a significantly depressed growth rate when compared to the control group (P < 0.05) and by 70 days both the medium and the high groups had significantly lower growth rates (P < 0.05). The high-dose group had a significantly (P < 0.05) lower specific growth rate (SGR) compared all other treatment groups at 35 days, although by 70 days these differences were not significant. The wet/dry muscle mass and muscle mass/total mass ratios, condition factor, and resting routine metabolic rates at both 35 and 70 days were statistically indistinguishable (P > 0.05) between treatment groups. All treatment groups assimilated the dietary MeHg into muscle tissue in a dose-dependent fashion. Percent assimilation was significantly lower (P < 0.05) in the high-dose group compared to the low-dose group at 35 days, (control 53%, low-dose 61%, medium-dose 50%, and high-dose 40%) but at 70 days assimilation was lower (35, 43, 42, and 32%, respectively) and statistically indistinguishable (P > 0.05) among the treatment groups. Dietary MeHg concentrations and bioaccumulation rates were correlated (r2 = 0.98 at 35 days, 0.99 at 70 days). These results may contribute to construction of ecosystem mercury models and more informed natural resources management at Clear Lake.
authors.affiliation: Department of Wildlife, Fish, and Conservation Biology, and Center for Aquatic Biology and Aquaculture, University of California, Davis, CA 95616, USA. aghouck@ucdavis.edu
authors.forename: Ann
authors.initials: A
authors.lastname: Houck
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Cech
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002140:California; D003530:Cyprinidae / Q000254:growth & development / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects*; D005618:Fresh Water; D008767:Methylmercury Compounds / Q000493:pharmacokinetics* / Q000633:toxicity*; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D013054:Spectrophotometry, Atomic; D013997:Time Factors; D036401:Toxicity Tests, Chronic
chemical_list: D008767:Methylmercury Compounds