How efficient has the selection programme from where
the improved experimental strain was obtained for this study
been over the 6 generations so far? This study estimated an
apparent realized response to selection for O. shiranus
growth of 25.2% at 6th generation. A realised response to
selection of 101% for harvest body weight relative to the
base population has been achieved within five generations
of selection in O. niloticus (Olesen et al., 2003). Although
our unimproved strain was a different species and may not
fully be equated to the O. niloticus base population, the estimated
selection response reported in this study for a comparable
number of generations is relatively low. Lower than
expected inter-generational genetic gains for harvest body
weight in this strain have also been noted elsewhere in relation
with low numbers of breeding candidates and resultant
low selection intensity (Maluwa and Gjerde, 2007) although
they do not seem very atypical and correspond with other
results of a selection programme in O. nilotiucs (Thodesen
et al., 2012).