Application of reproductive technologies to captive breeding programs for conservation of imperiled stocks of Pacific salmon
Captive breeding programs have been established to prevent extinction and aid recovery of imperiled stocks of salmonid fish in North America. Several reproductive problems limit their effectiveness, including early age of male puberty, asynchronous maturation of adults, inadequate development of secondary sex characters and behavior, and poor fertility. Contrary to commercial aquaculture, selective breeding cannot be used to solve these problems since preserving the genetic diversity of the wild stocks is paramount. Studies were conducted to improve broodstock management and mitigate these reproductive problems. Restricting body growth during the fall-winter period in yearling spring Chinook salmon significantly reduced the percent of males maturing at age 2; body fat levels affected maturation rates only in small fish (< 50 g). In females, restricting body growth reduced the rate of previtellogenic oocyte growth, but did not affect fecundity up to the late cortical alveolus stage. Implants containing gonadotropin-releasing hormone analogue were used to advance and synchronize spawning, without impairing fertility of adults spawned in captivity or spawning behavior in an artificial stream. Screening for Y-chromosome specific genetic markers, ultrasound and plasma sex steroid levels were tested as methods to identify gender and state of maturity. Maturing males could be identified 7 months prior to spawning using plasma 11-ketotestosterone levels, while ultrasound could be used 5 months prior to spawning. The GH-pseudo gene served as a genetic marker for male Chinook and coho salmon. Although these techniques improved effectiveness of captive breeding programs, egg fertility problems persist and habitat restoration remains as a significant impediment to success of stock restoration. Thus, new germ cell cryopreservation technology is being tested for stocks most at risk of extinction.