Artificial maturation of female Japanese eels by the injection of salmonid pituitary

Intramuscular injection of acetone-dried pituitary glands of salmonid fishes was carried out in 1971 and 1972.1. A weekly injection of four chum salmon pituitaries or eight pink salmon pituitaries into silver eels (per Kg body weight) produced conspicuous growth of ovarian eggs up to about one mm in diameter. Maturity factors of the treated eels ranged from 40 to 72 per cent. The oocytes corresponded to the migratory nucleus stage or pre-maturation stage. One eel treated with salmon pituitary naturally spawned a large number of mature eggs.2. Eels treated with hormones showed a striking increase in body weight with the commencement of maturation. The pattern of increase in body weight may be divided into four types. The coefficient of correlation between the maturity factor and increase in body weight was greatest in type A, followed by type B and D, but very low in type C.