During the experiment, one fish belonging to the unimproved
strain (stocking density of 7 fish/m3
) was observed to
be incubating some eggs in its mouth at a body weight of
6.3 g. This behavior occurred at a lower body weight than
the 8 g previously observed for this strain (Maluwa, personal
communication). All three strains had started breeding and
fry were found in all the hapas by the time the last two sampling
exercises were conducted. Precocious breeding is a major
problem in Malawian small-holder aquaculture because it
makes it hard to control fish densities and may lead to stunted
growth (Chirwa, 2009; Russell et al., 2008). Our results imply
that even the improved strain is prone to this problem; early
breeding may therefore undercut the benefits of the selective
breeding program.