Bath vaccination of rainbow trout (Oncorhynchus mykiss Walbaum) against Flavobacterium psychrophilum under field conditions in Chile

The trial was conducted during July–September 2011 (winter season), in a commercial fish farm, 30 kilometers to the East of Puerto Montt, X Region of Chile.

Fishes of local stock rainbow trout of 4 g of average weight, spawning in late April were used for the realization of this experience. The fish were kept in conditions of fish farming with open water flow, with spring water gravimetrically, filtered and 100% day light photoperiod regime and was separated into groups according to selection protocols. The fish during the 63 DVP were separated in 5 m³ tanks with continuous flow, with water average temperature for this time of the year (July–September) of 7.5±0.5°C, with a concentration of dissolved oxygen (DO) of 9 mg/L, with manual feed delivery three times a day and with initial rearing density of 4 Kg/m³.

Prior to the beginning of the experience, the pathogen–free status of the fish was confirmed by analysis for bacterial, parasitic and viral pathogens. Vaccination trial were conducted using a total of 20,000 of rainbow trout. Experiment was conducted in duplicate The four tanks for the experience were assigned as two vaccinated and two controls groups (number of fish and tanks identification are shown in table 1).

Flavomune® (Veterquímica S.A. Chile) inactivated bacterine against BCWD caused by F. psychrophilum, made with two virulents Chileans strains.

Half of the fish (10,000) were bath vaccination with Flavomune® diluted 1:10 in water for 1 min (Deep flushig) The other half of the fish (control groups) were sham–vaccinated with sterile TYES. (Figure. 1).

During all the trial, temperature and water quality of the tanks were registered 4 times a day. In addition, the mean body weight of the groups was recorded every 15 days. All the mortality was daily collected, recorded and analyzed subjected by standard protocol of necropsy. The date of sampling and weights are shown in table 2. Blood samples was collected 63 DPV, ELISA was performed with serum samples to identify anti–F. psychrophilum antibodies using C11–HRP Kit (Aquatic Diagnostics Ltd UK.).

Table 2: distribution of samples and weight, Flavomune

Environmental parameters
During the trial, 460 UTA were accumulated and the temperature variation is shown in figure 2. It parallels that of from normal conditions typical of this geographical area.

Figure 2: temperature slope July to September, 2011.

During all the assay, there were no differences in the tendency of growth between vaccinated and control groups both lines or profiles were in sharp increase, however vaccinated group growth rates were higher reaching equal–time growth 106% increase in weight compared to the control group (Figure 3).

Figure 3: growth Flavomune® experience July to September, 2011.

The daily mortality analysis revealed the existence of three peaks of mortality (July 15; and August 2) associated with outbreaks of RTFS, and the last one (August 17) was associated with the selection criteria of the farm (figure 4). After 63 DPV the control group had 3.9 time more mortality, than the vaccinated group (12.96 v/s 3.23%) as seen in figure 5.

The results of titration of antibodies using ELISA was 8 times higher in the vaccinated group than control group after 460 UTA post vaccination (Figure 6).

Figure 6: serum antibody responses of rainbow trout after 460 UTA post immunization.

Avendaño–Herrera R., Ilardi P. & Fernández J. (2009A). Significance of Flavobacterium diseases on salmonid farming in Chile 2nd Conference on Members of the Genus Flavobacterium. MGEN, Paris, France September 21–23, 2009. 10 pp.
LaFrentz BR., LaPatra SE., Jones GR., Congleton JL., Sun B. & Cain KD. 2002. Characterization of serum and mucosal antibody responses and relative per cent survival in rainbow trout, Oncorhynchus mykiss (Walbaum), following immunization and challenge with Flavobacterium psychrophilum. Journal of Fish Diseases. 25(12):703–713.
Lorenzen E., Brudeseth BE., Wiklund, T. & Lorenzen N. 2010. Immersion exposure of rainbow trout (Oncorhynchus mykiss) fry to wildtype Flavobacterium psychrophilum induces no mortality, but protects against later intraperitoneal challenge. Fish & Shellfish Immunology.28: 440–444.
Madetoja J., Lonnstrom LG., Bjorkblom C., Ulukoy G., Bylund G., Syvertsen C., Gravningen K., Norderhus E–A. & Wiklund T. 2006. Efficacy of injection vaccines against Flavobacterium psychrophilum in rainbow trout Oncorhynchus mykiss (Walbaum). Journal of Fish Diseases. 29(1):9–20.
Nematollahi A., Decostere A., Pasmans F. & Haesebrouck F. (2003). Flavobacterium psychrophilum infections in salmonid fish. Journal of Fish Diseases. 26: 563–574.
Tatner MF. 1985. The effects of vaccine dilution, length of immersion time, and booster vaccinations on the protection levels induced by direct immersion vaccination of brown trout, Salmo trutta, with Yersinia ruckeri (ERM) vaccine. Aquaculture. 46: 11–18.
Torroba M., Anderson DP., Dixon OW., Casares F., Varas A., Alonso L., Gómez del Moral, M. & Zapata AG. 1993. In vitro antigen trapping by gill cells of the rainbow trout: an immunohistochemical study. Histol Histopathol.8: 363–367.
Valdebenito S. & Avendaño–Herrera R. (2009). Phenotypic, serological and genetic characterization of Flavobacterium psychrophilum strains isolated from salmonids in Chile. Journal of Fish Diseases. 32: 321–333.