1. Chorions isolated from unfertilized eggs of medaka, Oryzias latipes, harden during incubation with Ca 2+ ions (Masuda et al., 1991).In this process, i.e

2. Under normal circumstances, only sexually mature male medaka have papillae, which develop on the joint plates of certain anal fin rays as a secondary sexual characteristic, providing a potential biomarker for endocrine disrupting effects.