Table 2 do not appear excessive for 350-m2 ponds. Note should also be
taken of the large variation in hybrid fingerlings produced when the same
density of females is used (Table 4), especially the zero figures.
To what extent reduced fingerling production exists in other hybrid
crosses is not known. Tal and Ziv (1978) state that the production of S.
niloticus x S. aureus hybrids is much lower than from single-species crosses.
Lessent (1968) also had problems obtaining all-male hybrid fingerlings by
crossing S. rnacrochir x S. niloticus in ponds. However, Hickling (1960)
stated that he had little problem producing S. mossambicus x S. hornorum
all-male hybrid progeny in ponds.
I have observed many cases of the all-male hybrid of S. niloticus x S.
hornorurn backcrossing with the female S. niloticus. In a pond containing
female S. niloticus, male S. hornorurn, and the all-male hybrid, the finger-
lings produced are fathered almost exclusively by the all-male hybrid. The
sexual behavior of the all-male hybrid appears to present fewer compatibility
barriers with the female S. niloticus than the male S. hornorum.
Whatever the causes, the low numbers of fingerlings produced and the
level of technology needed for pure-strain maintenance place restrictions on
the commercial culture of the S. niloticus x S. hornorurn hybrid. It is my
opinion, based on present knowledge, that the culture of all-male hybrid
tilapias is not to be recommended for the majority of farmers in tropical
developing countries where the financial resources to construct properly
designed hatcheries and hire qualified hatchery staff are lacking. Contamina-
tion of pure genetic strains of tilapia broodstock and backcrossing in spawn-
ing ponds are likely to occur. The governments in most tropical developing
countries do not have the money to build and staff hybrid tilapia hatcheries
to produce and distribute the fingerlings needed to culture this fish on a
wide scale. In most cases, for tiiapia culture to have a wide economic and
nutritional impact in a country, the private sector has to become involved in
fingerling production.
It is my opinion that some system of culturing a pure tilapia species is
better suited to most developing countries because the production of pure
species fingerlings can be accomplished with few problems by most farmers.
If the low production of fingerlings is the major disadvantage in culturing
all-male tilapia hybrids then the growout of hybrids to marketable size is the
major advantage. Stocking all-male tilapia without having to hand-sex is very
advantageous. The hybrids grow rapidly and uniformly when fed a wide
range of commercial and agricultural by-product diets. The addition of
chemical or organic fertilizers to pond water further increases production
and improves food conversion efficiency. Most tilapia hybrids are resistant to
disease and to low levels of dissolved oxygen. This allows high rates of
feeding and fertilizing resulting in elevated productions.
The culture of tilapia hybrids that are less than 100% male can also be
very profitable depending on the percentage of males and the size of the fish
to be marketed. Fish of about 200 g can be raised in 6 to 7 months with