• Salmonid Rickettsial Septicaemia (SRS) is a major disease affecting the Chilean salmonid aquaculture industry.
  • SRS is commonly treated by Florfenicol, a broad-spectrum antibiotic. Vaccines are registered for use against SRS but there is little evidence to support their efficacy.
  • Salmon offered Prefect in their feed had improved growth and lower mortality.


  • SRS is a major disease affecting the Chilean salmonid aquaculture industry. It is highly contagious and is associated with high mortality rates.
  • Although many vaccines for SRS are currently registered for use in Chile, there is little evidence to support the efficacy under field conditions. Florfenicol is a broad-spectrum antibiotic commonly used to treat SRS.
  • Prefect is an Acid Based Eubiotic (ABE) designed to support gut health formulated from a combination of free butyric, formic and propionic acids and their salts. Prefect also contains fructo-oligosaccharides (FOS).



A trial was conducted in Coho salmon at the Chinquihue Foundation to determine the efficacy of Prefect in the control of SRS in saltwater. Salmon were allocated to 1 of 7 treatment groups (Table 1). Vaccination was an injectable emulsion of an inactivated SRS vaccine.


Table 1. Treatment groups.

Treatment Group SRS Challenged Vaccinated Prefect Inclusion
Negative Control No Yes
Positive Control Yes No
Prefect D1 Yes No 1 kg/t
Prefect D2 Yes No 2 kg/t
Prefect D1+Vac Yes Yes 1 kg/t
Prefect D2+Vac Yes Yes 2 kg/t
Vaccinated Yes Yes

Groups challenged with SRS had 15 trojan fish added to each pen at day 179 for 39 days. Trojan fish had been intraperitoneally injected with a known amount of SRS pathogen (0.1ml of inoculum per fish) in this cohabitation challenge. Growth performance and cumulative mortality were assessed over course of the trial.


survival and average daily gain results

  • Prefect supplementation improved survival of salmon 39 days post SRS challenge (Figure 1).
  • Prefect supplementation increased weight gain and average daily gain (ADG) (Figure 2).
  • Dietary supplementation of Prefect at 2kg/t offered results comparable with vaccination alone and performance was further improved when used in conjunction with vaccination programmes.
  • These benefits could result in an additional income of US$3,840/month per pen.
  • Prefect is effective in maintaining and supporting salmon performance in the presence of SRS, with or without a vaccine, in the absence of antibiotics.