The Effectiveness of Prolonged Exposure on Soluble Antigen Uptake during Immersion Immunization of Fish

Immersion in bath suspensions for extensive time periods has been reported to enhance the uptake of particulate antigen by rainbow trout, Oncorhynchus mykiss. In order to determine if prolonged immersion also enhances soluble antigen uptake, juvenile rainbow trout, weighing 15 g, were immersed in BSA solutions at 15°C using exposure periods ranging from 3 minutes to 48 hours. BSA uptake, measured as plasma concentration, was significantly dependent upon the exposure period (p < 0.001), demonstrating that prolonged immersion enhances the uptake of soluble antigen as well as particulate antigen. Furthermore, we found that BSA uptake was significantly dependent upon the BSA concentration in the bath solution during prolonged immersion. The plasma BSA concentration Cp (μg/ml) after immersion was related to time and concentration by the equation Cp (Cb, t) = 3.47·10-3·Cb·√t, where t is the exposure period in hours and Cb is the BSA concentration of the bath solution (μg/ml). The correlation coefficient of this formula is 0.99. Thus, the optimal combination of exposure period and antigen concentration in the immersion solution can be selected.