A radioimmunoassay for blood and pituitary extract gonadotropin in salmonid fishes.

An antiserum was prepared by immunizing female rabbits with a purified preparation of chinook salmon gonadotropin (SG-G100). Using this antiserum and a highly purified chum salmon gonadotropin (G75) for radioiodination, a radioimmunoassay system was established which can measure 1.25 to 20ng/ml of salmon and trout gonadotropins. It was also suggested that this system can measure gonadotropin of the ayu which is often used as the experimental material in our laboratory, indicating this system could be applied to salmonina fishes. However, loach and frog pituitary extracts and higher vertebrate gonadotropins showed no cross-reaction. We could measure plasma or serum gonadotropin in the chum salmon and the rainbow trout with this system. In the chum salmon, an increased secretion of gonadotropin was observed at the time of ovulation as shown in other salmonids. The gonadotropin levels of ovulated salmon were significantly higher in freshwater than those in seawater. This result was discussed in relation to water metabolism of matured salmon prior to spawning.