Treating elvers of European eel Anguilla anguilla with mature carp ovary for 3–6 months during early growth induced female differentiation in 51·6–66·7% of treated animals compared with c . 5% in controls. The treatment also induced differentiation of ovaries in eels L T and a higher number of Syrski organs with ambisexual characters, and was most effective when administered at an early growth stage. The results could be attri...