PHEROMONE-INDUCED SPAWNING OF PACIFIC HERRING .1. BEHAVIORAL CHARACTERIZATION

A spawning pheromone in the milt (semen) and testes of the Pacific her ring, Clupea harengus pallasi, triggers spawning in sexually mature fi sh of both sexes and is thought to facilitate school spawning of this species. We found the response to the pheromone to be a stereotyped be havioral sequence consisting of a graded extension of the gonadal papi lla, release of gametes, and spawn deposition behavior. The response i s triggered by an olfactory stimulus, as demonstrated by the eliminati on of the response by occlusion of the nares. Stimulus concentrations of an approximate 1:500 dilution of fresh milt or the equivalent of 0. 02 g of fully mature testes per milliliter were required to elicit a r esponse in 50% of ripe herring that are responsive to the pheromone. F emale fish appeared to be less sensitive to the pheromone in milt than males early in the spawning season, but not thereafter. The average d uration of responses of male fish was longer after exposure to concent rated milt than to testes extracts, but no consistent difference in re sponse times of the two sexes was detected. Factors other than the spa wning pheromone, maturity of the fish, and stress also were found to i nfluence the spawning response. For example, exposure to shallow (3 cm ) water in a small tank induced ''spontaneous'' papilla extension and spawning approximately 20 min after refilling the tank; occluding the nares prevented this response. Also, the presence of floating kelp (Ma crocystis) resulted in prolonged spawning in a large tank after pherom onal stimulation. (C) 1997 Academic Press.