The sheepshead minnow as an in vivo model for endocrine disruption in marine teleosts: A partial life‐cycle test with 17α‐ethynylestradiol

Abstract

The sheepshead minnow (Cyprinodon variegatus Lacépède), an estuarine fish species, was exposed to 17alpha-ethynylestradiol (EE2) at nominal test concentrations of 0.2, 2, 20, 200, 400, 800, 1,600, and 3,200 ng/L. Fish were exposed for up to 59 d, from subadult stages to sexual maturity, under flow-through conditions. The exposure period was followed by an evaluation of reproductive success and survival of progeny. The reproductive success of exposed sheepshead minnows, as determined from data on egg production from two subsequent spawning trials, was reduced in fish exposed to 200 ng/L EE2 and, in one spawning trial, in the 20-ng/L treatment. Hatching success was reduced in the progeny of fish exposed to 200 ng/L EE2, but survival was good among fry that successfully hatched. Histological examination indicated generalized edema, damage to gill epithelia, hepatic toxicity, fibrosis of the testis, and evidence of sex reversal, including testes-ova and spermatagonia-like cells in ovaries. The maximum acceptable toxicant concentration (MATC) for gonadal development in males was within the normal range of EE2 concentrations in sewage treatment plant effluents. The exposure regimen and choice of test organism, combined with histological examination, allowed independent evaluation of ecologically significant acute, reproductive and estrogenic endpoints. Estrogen receptor-mediated effects occurred at concentrations where reproductive effects were measurable under standard reproduction assays. The sheepshead minnow appears to be a sensitive in vivo model for partial life-cycle testing of compounds that have the potential to disrupt the endocrine system as well as reproduction in estuarine and coastal marine fish species.

Long-Term Exposure to Environmental Concentrations of the Pharmaceutical Ethynylestradiol Causes Reproductive Failure in Fish

“…After 10 days exposure there was complete reproductive failure (no egg production) in the 50 ng/L EE 2 exposure group. These data support previous findings for high dosage, short-term effects of EE 2 (Lange et al 2001; Scholz and Gutzeit 2000; Seki et al 2002; Van den Belt et al 2002; Zillioux et al 2001), and this treatment was subsequently terminated. There were no effects, however, of any other estrogen treatment on numbers and viability of eggs from the F 0 generation at 14 hpf (Figure 2), embryo mortality in the F 1 generation ( F = 0.36, p = 0.78, n = 12), or impacts on larval integrity at 100 hpf; the proportion of developmental abnormality, hatch rate, and level of spine curvature were all not significantly different from controls; p > 0.05 for all cases.…”

“…A mean of 91.5% of the eggs were fertilized and survived to 100 hpf (posthatch) in all treatments before exposure and in control treatments throughout the experiment. This level of fertilization and survival is high when compared to similar studies on zebrafish (Hill and Janz 2003), sheepshead minnows ( Cyprinodon variegatus ; Zillioux et al 2001), and medaka ( Oryzias latipes ; Balch et al 2004), where lower survival (70, 65, and 62%, respectively) in controls probably relates to suboptimal breeding conditions or stresses associated with embryo culture.…”

“…Furthermore, these effects occur at concentrations that are at least an order of magnitude lower than for short-term exposures of mature fish proximate to spawning time; Seki et al (2002), Van den Belt et al (2002), and Zillioux et al (2001) provide other examples of lower sensitivity to adult-only exposure.…”

Multigenerational exposure of the estuarine sheepshead minnow (Cyprinodon variegatus) to 17β‐estradiol. I. Organism‐level effects over three generations

“…Zillioux et al [42] also reported oocyte atresia in sheepshead minnows exposed to EE2 except at the lowest concentration of 0.2 ng/L. In the present study, a substantial increase in oocyte atresia was seen in the two high-dose groups, with as many as 30 to 40 atretic oocytes seen in a single section of ovary.…”

“…Zillioux et al [42] also reported oocyte atresia in sheepshead minnows exposed to EE2 except at the lowest concentration of 0.2 ng/L. Zillioux et al [42] reported that sheepshead minnows exposed to EE2 displayed testis-ova at concentrations ranging from 20 to 800 ng/L. Fathead minnows exposed to E2 also showed an increase in atretic follicles compared to controls [44].…”