The role(s) of nitric oxide (NO) in fish gamete physiology is poorly understood but is likely to be significant. This project will focus primarily on the gametes of the steelhead to address this dearth of knowledge. Low doses of NO appear to enhance the motility of mammalian sperm; high doses are deleterious. The effects of NO on the motility of fish sperm are reported only in the fathead minnow. The motility of sperm from this fish is enhanced by low doses of NO and it is suspected that NO released from the egg facilitates fertility via this effect on motility. In light of the economic and environmental importance of salmonids, gaining a thorough understanding of their reproductive physiology is warranted and is necessary to optimize artificial reproduction; it is currently not known whether NO plays an important role(s) in the physiology of
their gametes. Our preliminary studies of Chinook salmon sperm are very suggestive and supportive and the current studies will examine the effects of NO on the gametes of hatchery-reared steelhead trout as well as Chinook salmon. The effects of NO on sperm function of fresh and cryopreserved sperm will be examined as will the effect(s) of NO on the egg and on fertility. This project will also address similar questions in the zebrafish. This fish has become a widely used experimental model, a great deal is already known about this fish, it is easy to maintain and it breeds year-round. Its inclusion is therefore complimentary to the primary focus on salmonids in these studies designed to elucidate of the effects of NO on fish gametes.