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Archived – Study to investigate protective effect of UV on fin abrasion

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Tank set-up at Sea Spring Hatchery. (Photo: Max Bothwell)

Tank set-up at Sea Spring Hatchery.
(Photo: Max Bothwell)


Now in its third year, a DFO co-funded study on the effects of ultra-violet radiation (UVR) on salmon fin abrasion is getting down to brass tacks. After two years of work with three strains of Pacific salmon, Dr. Max Bothwell of Environment Canada and Dr. Blair Holtby of DFO, will be narrowing their focus to one strain this year, and trying to determine the effect of stocking densities on a previously-demonstrated “protective” effect of UVR exposure in young salmonids.

The current work is being co-funded by DFO's Aquaculture Collaborative Research and Development Program (ACRDP) and Creative Salmon Company Ltd., a BC firm interested in improving the appearance and quality of chinook salmon for the high-end Japanese gourmet market.

A UVR paradox

Juvenile Big Qualicum Chinook. (Photo: Max Bothwell)

Juvenile Big Qualicum Chinook.
(Photo: Max Bothwell)


UVR is a short- wavelength, high-energy component of natural sunlight that has long been demonstrated to have a variety of negative effects on living organisms. The current investigations began in 2007 when Max Bothwell decided to follow up on previous anecdotal observations of juvenile coho. Young fish reared indoors or under cover developed badly abraded fins, while those reared in open tanks outdoors or in shallow “free-run” flumes consistently did not. This went against conventional wisdom about the damaging effects of UV, a nagging paradox that could have important repercussions for hatchery operations. Preliminary work in flumes and Capilano troughs with populations of coho fry confirmed the protective effects of UV radiation and ruled out the involvement of pathogens.

The project began with Bothwell and his BC team performing UVR exposure trials on Big Qualicum chinook pre-smolts. They were astonished to find no measurable difference between exposed and sheltered populations, an indication that the previously noted “protective” effect of UVR on coho fins might be species- or strain-specific, dependent on timing, or due to unknown factors.

In 2008 the team ran expanded trials at the Sea Spring Hatchery in Chemainus, BC, using three different strains of salmon: Big Qualicum chinook, Big Qualicum coho and Yukon chinook. Tanks were covered with either UV-transparent or UV-opaque Plexiglass, and image analysis software was used to quantify fin damage. Both the Big Qualicum coho and the Yukon chinook showed significantly higher fin-fraying without UVR exposure. The Big Qualicum chinook continued to appear unaffected, regardless of exposure. With lower stocking densities in these trials, the effects were somewhat less pronounced than previous observations, but remained significant.

In this final year of the current ACRDP funding, work is underway at Sea Spring’s hatchery to investigate in more detail the effects of stocking densities and UV radiation with Yukon chinook, the strain that Creative Salmon is interested in developing for their Japanese markets. Bothwell also wants to study hormone responses mediated by the pineal glands of fish under different conditions, seeking a possible mechanism for the apparent protective effect of UVR on fin health.

Future studies would allow the team to relate protective response to gradients of UVR intensity, timing and duration, both indoors and outdoors, and identify the exact physiological mechanisms responsible for the protection from fin abrasion in UVR-exposed fish. This could translate into direct health benefits for hatcheries and improved product quality across the industry.

Duration: Jan ‘08 – Oct ’09.
Funded by: DFO-ACRDP. Co-funded by: Creative Salmon Co. Ltd.
Project team: Blair Holtby (DFO), Max Bothwell (Environment Canada), Ted Groves (Sea Spring Salmon Farm Ltd.), Jake Etzkorn (DFO)
Research team: Blair Holtby (DFO), Max Bothwell (Environment Canada), Ted. Groves (Sea Spring Salmon Farm Ltd.), Jake Etzkorn (DFO).
For information, contact: Blair Holtby (Blair.Holtby@dfo-mpo.gc.ca)

Downloading radiation exposure data in the field. (Photo: Max Bothwell) Yukon chinook exposed to photoactive radiation (PAR) alone and to both PAR and ultraviolet radiation (UVR) show visible differences after five months. (Photo: Max Bothwell)

From left to right: Downloading radiation exposure data in the field. / Yukon chinook exposed to photoactive radiation (PAR) alone and to both PAR and ultraviolet radiation (UVR) show visible differences after five months.
(Photo: Max Bothwell)

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