The vaccines used by commercial fish farmers are not protecting fish from disease, according to a new study.
The study was compiled by researchers at the University of Waterloo, the Pontifical Catholic University of Valparaiso and Chile’s University of Valparaiso. It showed vaccinated fish tend to show more symptoms when contracting diseases, with the health impacts and ultimately deaths occurring as if they’d never received a vaccine.
“Today’s vaccines are marketed to fish farms as necessary disease prevention and are even required by some insurance companies, but they are not nearly as effective as needed under real world conditions.” said Brian Dixon, a professor in biology at Waterloo. “Some operators are giving five vaccinations per fish and then there are fish losses from the stress of receiving multiple handlings and injections.”
In the study, the researchers tested the efficacy of the vaccine for the bacterial pathogen Piscirickettsia salmonis by comparing the reaction of vaccinated and non-vaccinated Atlantic salmon when exposed to the sea louse Caligus rogercresseyi in the lab.
They found that although the number of bacteria living inside the fish was much lower in vaccinated fish, they showed many more signs of infection and a higher death rate compared with the unvaccinated group upon exposure to the sea lice.
The study concluded that once vaccinated, the salmon was unable to fight off multiple diseases at once. It’s first study showing how a parasite in fish can override the protective effects of a vaccine for another disease.
(This is a University of Waterloo press release – read in full on EurekAlert here).