A scientific article describes how salmon company SinkabergHansen successfully used bacteriophages to avoid mortality and poor fish health caused by yersiniosis.
Bacterial diseases are again on the rise in Norwegian aquaculture, but the industry currently has additional tools, other than vaccines and antibiotics, in order to deal with it. Salmon company SinkabergHansen used the bacteriophage product Custus®YRS for the first time in 2022, with results now published (article in Norwegian).
Custus®YRS utilizes bacteriophages to control the prevalence of Yersinia ruckeri, the bacteria that causes yersiniosis in salmon, and is globally the only biocontrol product of its kind.
The product is used to control the infection pressure in wellboats when transporting and delousing salmon. These operations typically cause a massive increase in the infection pressure inside the wellboat, as the salmon start shedding bacteria into the water. This process, coupled with stress related to handling, typically result in outbreaks of yersiniosis 1 -2 weeks later.
This is exactly what happened at two SinkabergHansen sites shortly after sea transfer in the autumn of 2021. About 5 percent of the salmon died, some 52 000 fish, in these first outbreaks of yersiniosis.
In accordance with the local production model, the fish was some months later to be moved from low-salinity sea sites to more exposed ongrowing sites further out in the fjord system. Given the disease history, this next transportation – in cold winter temperatures – would almost certainly trigger new outbreaks. The decision was made to use Custus®YRS in the wellboat to control the infection pressure during transportation.
16 trips were made to transport the fish to the high-salinity sites. None of them resulted in new outbreaks. Water analysis during transportation showed how the prevalence of Yersinia ruckeri increased at first, but only up until the Custus®YRS bacteriophages had completed its replication cycle and the bacteria were effectively destroyed.
During seven of the transportation trips Custus®YRS were used in combination with Ectosan® Vet sea lice treatment, and an interaction study was made to document any effects between the two substances. No such effects were detected.
182 after the transportation, yersiniosis mortality surfaced again after the second round of sea lice treatments, this time without the use of Custus®YRS. After this, the two affected cages needed one last sea lice treatment before slaughter, and to further study the effect of Custus®YRS, it was decided to only use Custus®YRS on one of these cages.
The result was another high-mortality yersiniosis outbreak in the untreated control cage, while the cage that used Custus®YRS during delousing did not suffer another outbreak.