Thomas A. Flagg

Competitive Differences between Newly Emerged Offspring of Captive-Reared and Wild Coho Salmon

Abstract We investigated competition among newly emerged fry from captive-reared and wild female coho salmon Oncorhynchus kisutch by conducting dominance challenges and growth and survival experiments in laboratory stream channels. Newly emerged fry from captive-reared females won a significant majority (72.7%) of dyadic dominance challenges against fry from wild females. In a growth and survival experiment conducted from emergence to 30 d postemergence, fewer captive brood fry died of apparent starvation when food was limited than wild fry, further suggesting a competitive advantage for the captive brood fry. All fry used in the study were paternal half-sibs, so observed differences between captive brood and wild fry were attributed to the maternal parent. We hypothesize that fry coloration resulting from differences in egg color between wild and captive-reared females may have influenced the observed competitive asymmetries. If so, such differences might be ameliorated by changes in husbandry practices ...

Effects of estradiol and diethylstilbesterol on sex reversal and mortality in Atlantic salmon (Salmo salar)

Abstract Atlantic salmon alevins were fed diets containing different doses of estradiol (20 or 2 mg/kg diet) or diethylstilbesterol (10, 1, or 0.1 mg/kg diet) for 60 days following yolk-sac absorption in an attempt to produce a monosex female population. Diethylstilbesterol or estradiol at the doses tested did not induce a greater percentage of females by April 1982, when the fish were 14 months old. However, at this time, in all estrogen treated groups, 5–17% of the fish had both ovarian and testicular tissue (intersex fish). Treatment of salmon with the high doses (20 mg/kg diet) of estradiol or diethylstilbesterol resulted in high mortalities, indicating that high doses of estradiol are toxic to the fish. We conclude that steroid treatment during the fishs developmental periods may not be feasible because of undesirable long-term effects. In January 1983, when the fish were 12 months old, 50% of the male controls were sexually precocious. By April 1983, 72% of the male controls had testes that were undergoing regression. We suggest that the sexual precocity observed in males in this study may be due to the 12L:12D photoperiod in which they were reared.

Introduction to a Special Section: Hatcheries and Management of Aquatic Resources (HaMAR)—Considerations for Use of Hatcheries and Hatchery-Origin Fish

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Methods and Accuracy of Sexing Sockeye Salmon Using Ultrasound for Captive Broodstock Management

AbstractUltrasound has been widely used to noninvasively examine the internal anatomy and reproductive status of many fish species. Since 2003, ultrasonography has been an integral part of broodstock management for Endangered Species Act–listed endangered Redfish Lake Sockeye Salmon Oncorhynchus nerka. Initial ultrasound screenings for each years broodstock were conducted 3 to 4 months prior to anticipated maturation, before external signs of maturation developed. In keeping with the natural life history of these fish, this permitted the separation of nonmaturing fish from maturing fish so the immature fish could maintain feeding and growth. It also permitted maturing seawater-reared fish to be transferred to freshwater for final maturation. Designing a spawning matrix to maintain genetic diversity requires knowledge of the sex of each fish before spawning. Approximately 1 month prior to spawning, a second ultrasound was performed to verify sex identification and thus ensure the accuracy of the spawning ...

Manchester Spring Chinook Broodstock Project, 1998-1999 Annual Report.

This yearly report concerned facilities upgrade and endangered Snake River spring/summer chinook salmon captive broodstock rearing.