Salmon farmer's alternative approach helps it turn the tide against Saprolegnia

Salmon producer Scottish Sea Farms (SSF) today said husbandry staff at its Barcaldine hatchery near Oban are seeing promising signs from a holistic approach to managing Saprolegnia, a naturally occurring air and waterborne genus of water mould that is specific to freshwater.

SSF was responding to questions about increased mortality at the recirculating aquaculture system (RAS) facility in the second half of last year, highlighted yesterday by anti-salmon farming activist Don Staniford after the publication of a Fish Health Inspectorate (FHI) report.

An FHI inspector visited Barcaldine on November 6 after SSF reported weekly mortality of 4.1 %, 4.7 %, 6.61 % and 6.8 % for the site in October – levels that are above the Code of Good Practice for Scottish Finfish Aquaculture reporting threshold. The fish deaths were due to Saprolegnia.

The inspector observed moribund and lethargic fish in all tanks examined in the pre-smolt area. Many presented with extensive lesions and fungus infection, despite being treated with Aquacen (formalin) and Cress (bronopol).

Aggressive and resistant

SSF said salmon producers are vigilant in monitoring for and managing Saprolegnia, something typically achieved by administering prescribed veterinary medicines, if required.

Since the second half of 2024, however, the pathogen had proven more aggressive and more resistant to traditional methods, with the result that Barcaldine had seen its normally high fish survival rates reduce, added SSF. In response, the company has taken a holistic approach, focused on boosting salmon’s natural ability to combat the heightened challenge.

SSF's head of freshwater Rory Conn said: “Since day one, Barcaldine hatchery’s RAS technology has afforded us more control than ever over growing conditions – water quality, oxygen and salinity levels, temperature, light – with minimal need for medicines. 

“When it first became apparent that the Saprolegnia present wasn’t responding in the same way to conventional methods, we did try increasing the frequency of treatments, but we still weren’t satisfied with the results.

Minimal handling

“So, we doubled down on our core principles of optimum growing conditions, good husbandry and minimal handling to help our young salmon mount the strongest defence possible against infection.

“Related to this, we know that fish’s natural immune response can be temporarily reduced following certain handling events or immediately after vaccination. So, we added the capacity to administer a brine solution during acute events as an alternative to veterinary medicines, the aim being to further help inhibit Saprolegnia but without compromising on water quality or fish welfare.”

Conn said the combined results of the alternative non-medicinal mitigation measures are encouraging.

“We now have fish that have been in the facility for 30 weeks and have not required veterinary medicine treatments, with survival rates returning to normal,” said the freshwater boss.

“Finding an effective response to the recent renewed Saprolegnia challenge has been a real team effort, but thanks to the collective input and determination of freshwater and fish health colleagues, we’re hopeful we have made an important advance.”

Veteran activist Don Staniford, who intends to contest SSF’s application for an interdict (injunction) keeping him away from the company’s property, visited Barcaldine yesterday, standing at the entrance to the site with a selection of anti-salmon farming placards. He was accompanied by retired lawyer and salmon farming opponent Ewan Kennedy, along with both a photographer and a videographer.

Staniford pointed out that Barcaldine had reported 662,000 mortalities in 2024.

Referring to photos of fish with lesions and fungus infection that were included in the FHI report, Staniford said “it is not surprising that Scottish Sea Farms are seeking an injunction banning myself and others from filming inside Barcaldine and other facilities”.