PHEROMONE-INDUCED SPAWNING OF PACIFIC HERRING .2. PLASMA STEROIDS DISTINCTIVE TO FISH RESPONSIVE TO SPAWNING PHEROMONE

A spawning pheromone in the milt (semen) and testes of the Pacific her ring, Clupea harengus pallasi, is thought to facilitate school spawnin g of this species. We found that responsiveness to the spawning pherom one was variable among ripe fish (milt-producing or ovulated). Measure ment of five principle reproductive steroids in the free form and five steroids in conjugated forms in the plasma of male fish early in the spawning season (newly ripe fish) showed that elevated plasma levels o f 3 alpha,17 alpha-dihydroxy-5 beta-pregnan-20-one and 17 alpha-hydrox yprogesterone coincided with responsiveness to the spawning pheromone in these fish; levers of other steroids did not differ. In contrast, r esponsiveness to the pheromone by female fish later in the spawning se ason (ripe-and-holding fish) coincided with lower levels of glucuronat ed 17 alpha,20 beta-dihydroxyprogesterone and a lower gonadosomatic in dex. We suggest that these differences indicate a more advanced mature reproductive state in the responsive individuals among both the newly ripe male and the ripe-and-holding female fish. We found no differenc es in the level of cortisol in the blood of the herring that could be correlated with differences in pheromonal responsiveness. We conclude that differences in responsiveness to the spawning pheromone coincide to some extent with levels of reproductive maturation but probably not with recent stress. (C) 1997 Academic Press.