Hormone-induced Ovulation of Coho Salmon (Oncorhynchus kisutch) Held in Seawater and Fresh Water

Abstract

Coho salmon (Oncorhynchus kisutch) mature and spawn naturally in fresh water. We investigated the feasibility of accelerating maturation and/or ovulation of coho salmon retained in seawater during the spawning season, and compared accelerated ovulation of coho salmon in seawater and in fresh water. Effective inducers of ovulation in salmon held in fresh water were partly purified or purified salmon gonadotropin followed 3 d later by luteinizing hormone releasing hormone analogue (LH-RHa); one injection of salmon pituitary extract (SPE); chum salmon pituitary (PIT) followed at 3 d by PIT; and one injection of 17α-hydroxy-20β-dihydroprogesterone. One injection of chinook SPE; coho SPE followed at 3 d by coho SPE; or partly purified or purified salmon gonadotropin followed at 3 d by LH-RHa were effective but to a much lesser extent in those salmon held in seawater. PIT followed at 3 d by PIT, or one injection of 17α-hydroxy-20β-dihydroprogesterane were ineffective in acceleration of maturation/ovulation of coho salmon retained in seawater. Cortisone or 20β-hydroxyprogesterone, which were only tested in salmon in seawater, also failed to elicit early ovulation compared with controls. We conclude that ovarian responses to the treatments of fish retained in seawater are reduced by osmoregulatory difficulties or high adult mortalities. Thus acceleration of ovulation of coho salmon held in seawater is not feasible at this time and requires further research.Key words: coho salmon, spawning, ovulation, induced breeding, gonadotropin, luteinizing hormone releasing hormone analogue