Effects of Dietary Methylmercury on Reproductive Endocrinology of Fathead Minnows

Abstract

Recent laboratory studies have demonstrated that environmentally realistic concentrations of dietary methylmercury can impair reproduction of fish. To evaluate relations between reproductive success and biomarkers of methylmercury exposure, we fed juvenile fathead minnows (Pimephales promelas) one of three diets contaminated with methylmercury: 0.06 (control), 0.87 (low), and 3.93 (medium) microg of Hg g(-1) dry weight. At sexual maturity, fish were paired, allowed to reproduce, and then analyzed for total mercury, plasma testosterone (T), and 17beta-estradiol (E2). Diets did not affect survival or growth of fathead minnows. Methylmercury suppressed levels of T in males and E2 in females. Male fathead minnows fed the control diet had mean T concentrations 20% and 106% greater than those fed the low and medium diets; control females had mean E2 concentrations 149% and 402% greater than those fed the low and medium diets. Methylmercury also inhibited gonadal development of females; the gonadosomatic index (GSI) of females fed the medium diet was 40% less than that of females fed control or low diets. Plasma levels of T in males and E2 in females were positively related to GSI. Methylmercury reduced the reproductive success of fathead minnows. Spawning success was 32% for pairs fed the control diet, 12% for pairs fed the low diet, and 0% for pairs fed the medium diet. Pairs fed the low diet required, on average, 5 d longer to spawn a clutch of eggs than the controls. Concentrations of methylmercury fed to fathead minnows in this study are also encountered by invertivorous and piscivorous fish in some methylmercury-contaminated aquatic ecosystems. This suggests that reproduction of wild fishes may be adversely affected by methylmercury and that suppressed hormone levels may be used to indicate diminished reproduction of fish.

Methylmercury accumulation, histopathology effects, and cholinesterase activity alterations in medaka (Oryzias latipes) following sublethal exposure to methylmercury chloride

“…The histological observation revealed that MMC treatment has comparatively overt bad effects on male medaka gonads, which indicated that MMC pollution might damage fish's reproductive system, thus leading to the procreation failure of the fish. Similar histopathological patterns found in other reports Canton, 1991, 1992;Drevnick and Sandheinrich, 2003) confirmed the results obtained above. A study concerning specific effects of various environmental pollutants including MeHg on the reproductive system of small freshwater fish species guppy (Poecilia reticulata) and medaka (Oryzias latipes) suggested that 1.8 ng/mL of MeHg induced the impairment of spermatogenesis (Wester and Canton, 1991).…”

“…las) indicated that reproduction of wild fishes may be adversely affected by methylmercury and that suppressed hormone levels may be used to indicate diminished reproduction of fish (Drevnick and Sandheinrich, 2003).…”

Kemp's Ridley Sea Turtle Saga and Setback: Novel Analyses of Cumulative Hatchlings Released and Time-Lagged Annual Nests in Tamaulipas, Mexico

“…Elevated levels of contaminants, including chlorinated hydrocarbons, in several other fish species are associated with reproductive impairment (Cameron et al 1992;Drevnick and Sandheinrich 2003;Hammerschmidt et al 2002;Longwell et al 1992), reduced egg viability (Billsson et al 1998;Giesy et al 1986;Mac and Edsall 1991;Matta et al 1997;Von Westernhagen et al 1981), reduced survival of larval fish (Berlin et al 1981;Giesy et al 1986), delayed maturity (Jorgensen et al 2004) and posterior malformations (Billsson et al 1998). Pesticide exposure in fish may affect antipredator and homing behavior, reproductive function, physiological development, and swimming speed and distance (Beauvais et al 2000;Moore and Waring 2001;Scholz et al 2000;Waring and Moore 2004).…”

Environmental contaminants and biomarker responses in fish from the Rio Grande and its U.S. tributaries: Spatial and temporal trends

“…Juvenile grayling (Thymallus thymallus) containing wholebody concentrations of 0.27 Ag/g resulting from dietary methylmercury exposure experienced permanent impairment of feeding efficiency and competitive ability (Fjeld et al, 1998). In female fathead minnows (Pimephales promelas), dietary methylmercury concentrations of 0.87 Ag/g dw (about 0.17 Ag/g ww assuming 80% moisture) increased whole-body Hg concentrations by more than 10-fold, suppressed hormone levels, and inhibited gonadal development relative to controls (Drevnick and Sandheinrich, 2003). It therefore appears that the greatest concentrations observed in fish from the RGB (~0.5 Ag/g) may be sufficiently high to represent a risk to the fish themselves.…”