Radioimmunoassay for salmon gonadotropin

Salmon gonadotropin (GtH) was purified from the pituitary glands of Chinook salmon Oncorhynchus tschawytscha. In addition, antiserum against the purified GtH was produced. Both the purified GtH and the antiserum were used to develop a radioimmunoassay for quantifying salmon GtH. The minimum detectable quantity of salmon GtH was 0.44 ng/ml (22 pg/tube). The intraassay and the interassay coefficients of variation were 6.0% (N=5) and 7.9% (N=6), respectively. The competition curves for plasma and pituitary samples of sahmonid fishes were parallel to the standard curve. Thus, this system was found to be suitable for the measurement of GtH in many salmonid fishes. However, pituitary samples of other teleost fishes showed low or no cross-reaction to this system. The salmon GtH RIA developed in this study was physiologically validated by detecting the ovulatory changes in plasma GtH levels known to occur in rainbow trout. Plasma steroid hormone levels were also measured and their roles in relation to GtH were discussed.