Egg thiamine content, length, weight and survival of steelhead (Oncorhynchus mykiss) exposed to three methods of experimental thiamine supplementation in 2022 and egg thiamine content from three Oregon hatcheries in 2019

Early rearing of steelhead (Oncorhynchus mykiss) in Oregon hatcheries is often problematic; fry can become emaciated and die during the period between hatch and first feed. Thiamine (vitamin B1) deficiency has caused early mortality in salmonids; however, thiamine status of Oregon?s anadromous steelhead populations is currently unknown. We sampled eggs of 7-10 females during spawning from three Oregon hatcheries in 2019. In 2022, females were injected with buffered thiamine HCl 50 mg/kg prior to spawning; additionally, a subset of eggs were supplemented via bath treatment with thiamine mononitrate (1000 ppm) at spawning. We then compared egg thiamine from control and injected females, as well as measured mortality and growth in fry for 8-weeks post-hatch from control, egg baths of thiamine, injection-only, and both injection and baths. These data identify thiamine deficiency in Oregon steelhead and suggest supplementation with thiamine can mitigate impacts to survival during early rearing.