The low and non-significant heritabilities of specific antibody production against V.
salmonicidu or V. anguillurum O-antigens estimated in the present experiment indicate
that these traits would not be promising candidates as immunological markers in a
breeding program. However, the rather high and significant genetic correlations between
some of the markers and with survival during the sea water period indicate the presence
of an interesting genetic component. The infection status in the experiment could be
responsible for the low heritability estimates. The most important observation in this
study was the correlation between the survival data in the sea water period and the mean
antibody concentration against O-antigens in the corresponding half-sib group at the first
sampling. Whether this reflects specific cross-reacting antibodies between the antigens
or naturally occurring non-specific cross-reacting antibodies was not studied, but there is
a possibility that antibody concentration recorded at a single sampling on fish exposed to
environmental antigens only, without prior immunisation, could be used as a selection
criterion. This prospect should be further investigated.