HENDERSON: The question is, is the growth improvement which you observe for the
hybrids comparable to that for the sex-reversal treatment alone?GUERRERO: We found significant differences in growth of normal males and those
which are sex-reversed females. The latter remain slower growers compared with the
normal males and with all-male hybrids.JALABERT: Dr. Lovshin, in your maintenance of pure strains, have you seen any signs
of adverse affects of inbreeding?LOVSHIN: It is difficult to say. We suspect a reduction in growth rate but we have to
check this. The Sarotherodon niloticus and aureus used at Auburn University, elsewhere
in the USA and some of the Latin American work all stem from an initial introduc-
tion to the USA of about 25 individuals of each species from the Ivory Coast. Over the
years, we kept about 25 or 30 broodstock of each species and we let them reproduce.
Every six months to one year, we would clean everything out and replace the broodstock
with 25 or 30 younger fish.JALABERT: This is not a large enough population.LOVSHIN: I agree with you.HENDERSON: Incidentally, there was a consultation meeting in Rome in June 1980
sponsored by UNEP on the conservation of genetic stocks of fish. One thing that did
come out of this was a recommendation on the minimum size of the stocks which you
need keep to avoid the problems of inbreeding. I can provide an overview of this meeting
to anyone who is interested.
EDITORS: In Panama, the cross S. niloticus 9 x S. hornorurn d male has now been aban-
doned for all-male hybrid production in favor of the S. rnossarnbicus 9 x S. hornorurn d
cross. This gives very high fingerling production and 100% males. Fry are reared in
earthen ponds and then grown to fingerling size in open concrete ponds as in the Ivory
Coast (see Coche, this volume). This information was received from R. Pretto Malca.