An enzyme-linked immunosorbent assay for lipovitellin quantification in copepods: A screening tool for endocrine toxicity

Vitellogenin (VTG) has been widely used as a biomarker of estrogenic exposure in fish, leading to the development of standardized assays for VTG quantification. However, standardized quantitative assays for invertebrate, particularly crustacean, lipovitellin (also known as vitellin [VTN]) are lacking. In this study, a fluorescence‐based VTN enzyme‐linked immunosorbent assay (ELISA) was developed to quantify microquantities of VTN in the estuarine, sediment‐dwelling copepod Amphiascus tenuiremis. This ELISA utilizes a VTN‐specific polyclonal antibody developed against amphipod (Leptocheirus plumulosus) embryo VTN and exhibits specificity toward female copepod proteins. In routine assays, the working range of the ELISA was 31.25 to 1,000 ng/ml (75–25% specific binding/maximum antibody binding [B/B0]) with a 50% B/B0 intra‐ and interassay variation of 3.9% (n = 9) and 12.5% (n = 26), respectively. This ELISA is capable of detecting VTN as low as 2 ng/ml, and can accurately detect VTN in as few as four copepods. The ELISA significantly discriminated positive (gravid female) and negative (male) samples, and was suitable for screening endocrine toxicity in copepods. Stage‐I juvenile copepods were individually reared to adults in aqueous microvolumes of the phenylpyrazole insecticide, fipronil, and whole‐body homogenate extracts were assayed for VTN levels. Fipronil‐exposed virgin adult females, but not males, exhibited significantly higher levels of VTN relative to control males and females. This crustacean VTN ELISA is likely useful for evaluating endocrine activity of environmental toxicants in copepods and other crustacean species.