in three ponds, which were randomly assigned to
a block of 6 ponds. The 6 earthen ponds were
250 m2 with 220 m3 water per pond. Hybrid C1aria.s
(C. macrocephalus x C. gariepinus) of 13- 17 g size
were stocked in cage of 4 m' (2 m x 2 m x 1 m) at a
density of 220 fish/m2, which equaled to 275 fish/m3
as each cage was submerged only 0.8 m in 1-m deep
ponds. The cages were made of metal frame and rigid
PVC nets with 0.5-cm meshes. To maximize the water
exchange those cages were suspended 0.2 m above the
pond bottom near the center of each pond. Cages were
brushed monthly to remove attached algal growth.
Tilapia fingerlings with average weight of 6-7 g were
stocked at a density of 2 fish/m3 in the open ponds,
or 220 fishlpond. To prevent reproduction problem,
tilapia were sex-reversed with methyl-testosterone.