both crosses, the most advantageous sex ratio was three females to one male
and the breeding success was much higher for the intraspecific S. niloticus
cross. The average monthly production of S. niloticus fry was 1,32O/cage:
equivalent to 880/m2 or 1,466/m3.
Table 3. Some results of tilapia fry production in 0.9 m3 mosquito net cages (hapas) at
total stocking rates of 8 to 12 fish of individual weight 90 to 135 g er cage. This stock-
ing rate approximates to 5.3 to 8.0 fish/m2 or 8.9 to 13.3 fishjrn B (Guerrero 1979a).No. of fry No. of fry
Spawning Cross Sex ratio produced produced % of spent
Male Female (Male:Female) per cage per female femalesS. niloticus x S. niloticus 1:5 1,660 309 53
1:3 1,647 - 407 67S. niloticus x S. mossambicus 1:5 509 280 18
1 :3 527 458 19A similar system has been proposed by the Aquaculture Department of
the Southeast Asian Fisheries Development Center (SEAFDEC) for small-
scale operators of S. niioticus cages in the eutrophic lake Laguna de Bay,
Philippines (Radan 1979). Six to seven broodstock/m3 of water are placed
in hapas at the 1:3 sex ratio. Every 3 to 4 weeks, an average of 250 fry/
spawner are collected. These are sorted by size and reared in further hapas at
densities of either 500/m3 (no supplementary feeding) or 1,000/m3 (feeding
with algal cake), until ready for transfer to growout cages after 1 to 2
months.At Lake Kossou (Ivory Coast), S. niloticus fry were regularly produced
in relatively large numbers using two earth ponds, 30 x 20 x 0.4 m deep
(Campbell 197813). Large female fish and smaller males (mean weights 700
and 200 g) were stocked at an average density of 0.5/m2 with a 1:4 to 5 sex
ratio in one pond. Intense supplementary feeding on a diet exceeding 30%
protein was provided for one month. The broodstock were then removed
with a cast net and transferred to the second pond where the treatment was
repeated. Intense supplementary feeding was continued in the first pond for
one more month at the end of which about 5,000 3 to 4 cm fry were
harvested. This pond was then immediately restocked with the broodstock
removed from the second pond. Such a culture system can therefore produce
each month an equivalent of 4.2 fry/m2 pond or 10.4 fryjfemale, much
lower production figures than those reported above from hapas.
The fry produced in the ponds in two months were then transferred to
1 m3 floating cages with 8 mm mesh at a stocking density of 1,000 fry
or more per cage. For two months, a com@ete feed (25% protein) was given
at the daily rate of 10 to 8% of the biomass. A first selection of 20 to 30 g