Reactions of the key enzymes in steroidogenesis were demonstrated histochemically in the tissues of the immature Chum salmon, Oncorhynchus keta, reared in a saltwater pond. Activities of enzymes associated with the biosynthesis of steroid hormones were also observed in the fish tissues.
1. A positive reaction of the key enzyme, 3β-hydroxysteroid dehydrogenase, related to steroidogenesis was detected only in the tissues of the interrenal gland in the head kidney of the fish.
2. Reaction of the key enzyme, 17β-hydroxysteroid dehydrogenase, related to steroidogenesis was not detected in the tissues of the organ of fish examined.
3. The reaction of the enzyme, glucose 6-phosphate dehydrogenase, was observed in the tissues of the fish organs examined.
4. The reaction of the enzyme, isocitrate dehydrogenase, was observed slightly in the tissues of organs such as nephron of the mesonephros, liver, interrenal gland and cardiac muscle of the fish.