The Biology and Culture of Tilapias

now being applied to tilapias also, although still on a relatively small scale

(Rabelahatra 1979). For example, in Cianjur large submerged bamboo

cages (5 x 4 x 0.7 m deep) are stocked with S. mossambicus fingerlings

(mean weight 20 g; stocking rate 0.7 kg/m3). This yields 50 to 60 kg of

fish in six months, which corresponds tdan average monthly production of

about 0.55 kg/m3: a little less than the production realized in Laguna de

Bay by Pantastico and Baldia (1979), see above, but only about half of that

obtained by commercial farmers in eutrophic lakes (see Table 4).

Table 6. Summary of data from the culture of all-male Sarotherodon niloticus stocked in
0.5 m3 cages at 200 fish/m3 in a pond receiving heated water effluent (25 to 37'~) from
a nuclear power plant at Tiange, Belgium (after Philippart et al. 1979). Bracketed values
are representative of the range of fish sizes.

Pmi (I) Bi (kglm3) B~ (kg/m3) G (Jd) MSG (%I MP (ktlms) DRIB (8)

-- -- -

* duplicate experiments

Pmi : mean weight at stocking

Bi : mean biomass at stocking

: mean biomass at harvest

: average growth rate of individual fii during the culture period

MSG : average monthly specific growth rate as % Pmi for^30 days

MP : average monthly production (Bf - Bi) observed and recalculated on a 30-day

basis.

DRIB : daily rate of increase of the biomass calculated from Bf = Bi (1 + i)" where n

is the culture period in days and i is Dm

100

Semi-Intensive Culture

1. DEFINITION

In semi-intensive operations some supplemental feed is 'given but in

contrast to intensive operations, this feed is usually relatively poor in protein

(less than 10% dry weight) and made from local materials readily available at

low cost. Semi-intensive cage culture of tilapias uses mainly phytophagous

species which receive vegetable material or agricultural by-products as

supplementary low-protein diets in the presence of algal blooms.

A caged monosex male population of T. guineensis in a thermal effluent