The Biology and Culture of Tilapias

Every little puddle is a potential hiding place and small fry and fingerlings
can live for weeks in a footprint filled with water. Partial pond filling before
poisoning facilitates the elimination of fish in many small holes. Screens
filtering pond water supplies should be checked daily and repaired when
needed. Predatory birds should also be controlled.
Broodstock "families" that have produced sufficient numbers of hybrid
fingerlings are immediately transferred to a freshly prepared spawning pond
where a new 2.5 month cycle is begun. Broodstock "families" that have not
given adequate fingerling numbers are eliminated and new broodstock are
used. Broodstock "families" that produce low numbers of hybrid fingerlings
in the first spawning cycle will usually produce poorly on subsequent spawn-
ing cycles.
Preliminary studies, (Lovshin 1980) have shown that broodstock used
for more than one spawning season should be replaced because of declining
fingerling production after 3 to 4 hybridization cycles or when the brood-
stocks are 14 to 17 months old: assuming they were stocked when sexually
mature at 5 to 6 months old. The average number of hybrid fingerlings
produced in a 350-m2 pond when 50 female S. niloticus are stocked with
50 male S. hornorum is approximately 2,700 in 2.5 months.
Berrios-Hernandez (1979) demonstrated that cannibalism by finger-
lings on newly hatched fry greatly reduced fingerling production of S. aureus
in 7-m2 plastic pools. Partial harvesting of the fry at weekly intervals in-
creased fingerling production 35 times compared with total fingerling harvest
after a 4 month spawning period. Initial studies done in Pentecoste, Brazil
have not been able to demonstrate an increase in hybrid fingerling produc-
tion with partial harvesting at 10 day intervals. While cannibalism by finger-
lings is an important factor in fry survival in confined environments, it is not
known what influence cannibalism has in a larger spawning pond environ-
ment. When hybrid spawning ponds are drained, an attempt should be made
to grade and stock hybrid fingerlings and fry separately to minimize cannibal-
ism in nursery ponds.
Pretto-Malca (1979) describes a system, similar to that used in Brazil, to
produce S. niloticus x S. hornorum hybrids in Panama. The principal differ-
ence is that the all-male hybrid fry are partially harvested at 5 day intervals
with a fine mesh seine and transferred to concrete tanks for further growth.
The hybrid fry and small fingerlings are graded by size for stocking into
separate tanks to reduce cannibalism. The fry are fed zooplankton in the
concrete tanks.
Mires (1977) and Morissens (1977) outlined the procedure used in Israel
to produce hybrid fingerlings of female S. niloticus and male S. aureus
(Figure 2). The hybrid fingerling production system used in Israel is more
complicated and time-consuming than the hybrid fingerling system used in
Brazil and Panama because of the temperate climate, lack of genetic purity
of the broodstock, and the need to handaex the less than 100 percent male
hybrid fingerlings. Pure genetic strains of S. niloticus and S. aureus are
selected electrophoretically and the broodstock placed in aquaria to spawn.
The pure S. niloticus and S. aureus fry produced are either raised in the
laboratory until reslching 50 g or raised in the laboratory up to 2 to 3 g when
they are transferred to earthen ponds for growth to 50 g. After reaching