Managing for IHNV in Rainbow Trout at Leaburg Hatchery Erik Withalm erik.j.withalm@state.or.us
Background Mitigate for lost recreational fishing opportunities due to the construction of Blue River and Cougar dams Rear 700,000 legal rainbow trout per year 400,000 eggs were historically hatched onsite Water source: McKenzie River
Infectious Hematopoietic Necrosis Virus (IHNV) at Leaburg Isolated in rainbow trout in 1995 First major outbreak in August 2002 Most severe in July, August, & September Source of IHNV is found to be summer steelhead migrating over Leaburg dam Native trout population suspected as additional reservoir
Changes to Rainbow Program Only stock waterbodies where IHNV has been positively identified in fish Off site early rearing of production fish Rearing densities lowered by 27% Produces a better looking fish Less fin nip and parasite problems Sentinel fish hatched on site Repository for fish exposed to IHNV from other hatcheries Alternative to euthanization
Off Site Early Rearing Production fish early reared at IHNV negative hatcheries Fish are already graded, fin clipped, and received at final pond densities Sizes range from 20 fish/lb to 3 fish/lb depending on time of transfer
Off Site Early Rearing (cont.) 300,000 fish received in mid to late fall for stocking January-June June Cooler temperatures Increased flows 100,000 fish received in several shipments after June for stocking through December Maintain minimum number of fish July-Sept. 250,000 fish destined for IHNV negative waterbodies are liberated directly from other facilities
Rainbow Trout Mortality Attributed to IHNV 25 Percent of Total Annual Rainbow Trout Inventory 20 15 10 5 0 2002 2003 2004 2005* 2006 2007 *Increased mortality in 2005 as a result of receiving fish already infected with IHNV from another facility.
Experiments Vaccine trial Top dressed feed with killed IHNV particles Inconclusive results Feed additives Beta glucans Nucleotides Vitamin packs Accelerated growth program
Accelerated Growth Program Goal: Produce a legal sized rainbow trout (3 fish/lb ; 150g) in 9 months Started fish on 50 F F well water (8-9 F F above river water) Avoided internal fungus and coldwater disease Limited well water supply Switched to heated river water (53 F) Ponded fish outside at 20 fish/lb Aggressive feeding schedule Attained legal size in 7.5 months
Accelerated Growth Chart Fish Size (g) 300 250 200 150 100 50 0 Control Accelerated Legal size 3 fish/lb (150g) x Mar Apr May June July Aug Sept Oct
Accelerated Growth Program (cont.) Greater flexibility for trout stocking program Utilize fall spawning 53 stock and winter spawning 72 stock Potential to push fish to an even greater size Trophy trout program (1.5 fish/lb and larger) UV disinfection unit to be installed in hatch house Increased clean water supply Shorter time on river water means less exposure to IHNV
Conclusion The rainbow trout program is very complex, with every year producing a new set of challenges. From 2002 to 2007, no stocking program has been the same. The most effective management tool we have is the ability to minimize fish stress and viral exposure. Until Leaburg acquires a whole hatchery UV disinfection system, we will continue to adapt to the challenges of IHNV in order to meet annual production goals.
Acknowledgements Timothy C. Wright, Manager, Leaburg Hatchery John Kaufman, Virologist, ODFW Tony Amandi, Pathologist, ODFW