Measurement of immunoreactive alpha-melanocyte-stimulating hormone in the blood of rainbow trout kept under various conditions.

Initial attempts to measure alpha-MSH in trout blood by radioimmunoassay proved unsuccessful due to apparent losses of immunoreactive hormone, especially in the plasma of trout adapted to a black background. An extraction protocol for alpha-MSH from plasma is described. Subsequent radioimmunoassay revealed progressive increases in immunoreactive alpha-MSH as trout became adapted to a black background. Plasma alpha-MSH titres were raised during fungal infection, and also showed significant differences in fish obtained from different fish farms.