Pathogen Piscirickettsia salmonis has caused high mortality rates in the salmon industry since 1987. (Photo: ucv.cl/S Bravo/NACA/FIS)
Salmon mortality rate on the rise due to rickettsial syndrome
Monday, June 25, 2012, 02:30 (GMT + 9)
For a time there has been an increase in the number of salmon deaths due to the pathogen Piscirickettsia salmonis, which is responsible for rickettsial syndrome (SRS) in the Chilean salmon industry.
However, from the Technological Institute of Salmon (Intesal), under the Association of Salmon Industry AG (SalmonChile), it is ensured that mortality rates are lower than those recorded before the crisis caused by the outbreaks of the infectious salmon anemia (ISA).
"In no case is the percentage similar to pre-crisis levels," clarified Rolando Ibarra, supervisor of the Intesal Department of Health and Production.
According to the data provided by the entity, the average monthly mortality rate of Atlantic salmon during the first quarter of 2007 was 1.44 per cent while in the same period of 2012 it was 0.22 per cent.
The same happened with trout: in the first three months of 2007, mortality rate reached 1.35 per cent while in the first quarter of 2012 it only reached 0.7 per cent.
"It’s important to highlight that the appearance of the disease in salmon can often be multi-factorial. Environmental, fish and pathogen factors can be taken into account," Ibarra added.
"Although it is an important part of the equation, production is not the only component," he stated.
According to Ibarra, several conditions take place to account for the increased prevalence of SRS.
"Precisely as a result of the health measures adopted and of the current regulation, the prevalence is totally different from the old production model. The model has also been designed to stop pathogen cycles and prevent the spread of these among neighbours," explained Aqua.
The most affected species by SRS is the trout, which is followed by Atlantic salmon and by Pacific salmon, occupying second and third position respectively.
As to the efficacy of the vaccines, Ibarra noted that while all those registered by the Agricultural and Livestock Service (SAG) have documented efficacy, in the field several factors take place, such as the quality of the fish, the vaccination technique, the vaccination temperature and the exact knowledge of the protection period.
"In general, outbreaks [and most losses] are produced in the last third of the production chain and the protection provided by vaccines would not be guaranteed until that period," Ibarra noted.
He also announced that Intesal will conduct a study to establish the efficacy of those vaccines that are commercially available for trout and for Atlantic salmon.
The results could be ready by the end of this year, "at least for the early stages," stated the supervisor of Intesal Department of Health and Production.
On the other hand, excellent results were provided by an investigation led by Jaime Figueroa, a researcher at the Institute of Biochemistry and Microbiology of the Faculty of Sciences of Universidad Austral de Chile (UACh), who succeeded in isolating 42 strains of the pathogen Piscirickettsia salmonis.
The study was funded by Innova Chile of the Corporación de Fomento de la Producción (Corfo).
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