“…Such phenomenon has been reported in Chinook salmon (Oncorhynchus tshawytscha), rainbow trout (Oncorhynchus mykiss) and Atlantic salmon (Salmo salar L.), in these species, both the frequencies and the antibody level of the responses can by highly variable [35,36]. In our study, though antibody levels to various protein antigen seemed increase during the experiment period, the tendency was not always constant, the variety of the antibody response of individuals from the same group and the small sample (n ¼ 5) may take account for it.…”