“…The progestogen 17,20fl-dihydroxy-4-pregnen-3-one (17,20tiP) was first identified in plasma of Pacific salmon (Oncorhynchus nerka, Salmonidae) by Idler et al (1960), and later studies showed it to be the most effective steroid in inducing GVBD in pike (Esox lucius, (Jalabert, 1976;Goetz and Bergman, 1978;Nagahama et al, 1983). More recent studies in four cyprinids Cyprinus carpio, Labeo rohita, Cirrhinus mrigala and Catla catla (Epler, 1981;Inbaraj and Haider, 1988;Haider and Inbaraj, 1989), the siluriform Mystus vitattus (Bagridae) (Upadhyaya and Haider, 1986), the Japanese whiting (Sillago japonica, Sillaginidae, Perciformes) (Matsuyama et al, 1990b) and the marine flatfish Limanda limanda (Pleuronectidae) and Pleuronectes platessa (Pleuronectidae) (Canario and Scott, 1990a) have confirmed its efficacity in other species. In some of these cases, however, other steroids such as 17,20fl,21-trihydroxy-4-pregnen-3-one (17,20fl,21P), 5-pregnene-3fl, 17,20fl-triol (17,20fl-P5), and 11-deoxycortisol (17,21-dihydroxy-4-pregnene-3,20-dione; 17,21P) have comparable activity to that of 17,20tiP, while a number of other steroids, including 5fl-reduced compounds, have significant activity.…”