Physiological effects of an oil-adjuvanted vaccine on out-of-season Atlantic salmon ( Salmo salar L.) smolt

Abstract

Three groups of out-of-season smolts (0+) were studied; untreated smolt (UT), smolt injected with a multivalent commercial oil-adjuvanted vaccine (VA), and smolt injected with the same oil-adjuvanted formulation without the vaccine components (AD). The 0+ smolts were induced by photoperiod and temperature manipulation. Growth, serum concentrations of proteins and IgM, and seawater tolerance were measured. Growth of VA-injected smolt was significantly reduced from three weeks post vaccination until two weeks after seawater transfer when compared to UT and AD. This indicates that vaccine antigen or the antigens in combination with adjuvant can cause reduced growth rates as previously reported using oil adjuvanted vaccines. One week after vaccination, the serum protein levels were significantly higher for UT fish compared to both VA and AD groups, but no significant differences were seen thereafter until seawater transfer. After seawater transfer, both VA and AD groups had significantly higher serum protein levels than the UT group. The serum IgM level increased after vaccination in the VA group and after seawater transfer was more than four times higher than in the UT group. At the same time, the AD group had an approximately 50% higher serum IgM level than UT fish, indicating that the oil-adjuvant alone stimulates IgM production. Using 96-h seawater challenge tests, there were no differences in seawater adaptability between UT, AD and VA treatments. The results show that the oil-adjuvanted vaccine had a negative effect on growth, and elevated IgM levels prior to seawater introduction, but had no negative effect on smoltification.