In the Philippines, using a relatively cheap feed (moist pellets at US$0.17/
kg), Guerrero (1979a) appears confident of producing within 2 to 4 months
80 to 100 g marketable tilapias with FCR 2.5 after stocking at 5 to 20 g.
An average production of 12 to 20 kg/m3/month is attainable,givini an esti-
mated monthly net income of US$6.75 to 10.80/1 m3 cage.
Coche (1977) reports culture trials in the artificial Lake Kossou (Ivory
Coast), from 1974 to 1975 beginning with 1 m3 cages and pelleted chicken
feed (24.7% protein). These demonstrated the excellent potential of S.
niloticus intensive cage culture. Although reduced DO'S were encountered
for most of the culture periods, growth rates were usually about or above
1.2 glday and the monthly production ranged from 9 to 15 kg/m3, with fish
densities and initial biomasses in the normally accepted range. Low feeding
efficiencies were due mostly to the inadequate feed (which contained
up to 30% undigested maize middlings) and to excessive DFR's. Campbell
(1978b) used three improved feeds (Table 9--B1, B2, B3) and reduced DFR's
in larger cages. His lower initial biomasses and densities (relative to cage size)
resulted in better growth rates (1.4 to 2 g/day) but gave lower average produc-
tions with increasing cage size. Smaller cages (6 m3) produced 9 to 11 kg/
m3/month and larger ones (20 m3) 2.6 to 3.7 kg/m3/month. Feeding effi-
ciency was much better than Coche's (1977) results: FCR's, 1.9 to 2.2. It
should be remembered, however, that Campbell used on average 84% male
populations.
N'Zimasse (1979) used a heavily manured fish pond in the Central African
Republic. The results are difficult to assess because of DO deficiencies, but
the survival of S. niloticus was excellent. The growth rate, production and
feeding efficiency were poor, especially for all-male populations.
Philippart et al. (1979) used increasing densities (up to 600 fish/m3)
and biomasses in pond-based cages in a thermal effluent. The feed was very
rich in protein (46%). Neither growth rates nor FCR were as good as could
have been expected in such small cages. The DFR was probably too high
considering the size of the fish and the food quality. Good production was
obtained with the two highest densities/biomasses, but at the cost of low
feeding efficiencies.
Only limited data are available on the intensive cage culture of all-male
S. niloticus. Coche (1977) suggested this as one way of increasing production:
his fish, stocked at average weight 49 g, grew at an average rate of 1.8 g/day
and gave a production of 15.1 kg/m3/month on relatively poor quality feed.
In the Central African Republic, N'Zhasse (1979) obtained poor results
because of deficient environmental conditions and in Belgium (Philippart
et al. 1979), the results for all-male culture were not as good as expected,
although the feeding efficiencies were increased by adapting the DFR's to
the fish sizes. Strangely enough, higher average production was experienced
with smaller biomasses, which calls for some caution in interpreting these
results. The relative brevity of the experiments might be partly responsible.
It appears that further data are needed to assess the potential of monosex
cage culture.
Table 14 summarizes the results of the intensive cage culture trials with