pared for a new spawning period while the fry are growing in the rlursery
pond below. These ponds should allow for continual production of tilapia
hybrids, increased survival of hybrid fry and fingerlings, reduced amount of
labor needed to drain spawning ponds, and conservation of water (as water
from the spawning pond can be used to fill the nursery pond). It still remains
to be determined if the above advantages will offset the added cost of
building these spawning-nursery ponds.
Consistent production of all-male tilapia hybrids in earthen ponds takes
more dedication and care than any other tilapia fingerling production
system.
GrowthOne of the apparent advantages of culturing male hybrids is their in-
creased growth potential. Hickling (1968) notes that male hybrids produced
by crossing S. mossambicus with S. hornorum grew faster than either parent
stock. Kuo (1969) compared the growth of hybrids produced by crossing S.
mossambicus x S. niloticus, hybrids of the reciprocal cross, and pure S.
mossambicus and S. niloticus fingerlings in 600-m2 earthen ponds. The fish
were stocked at l/m2, fed a ration of rice bran and peanut cake, and were
harvested after 122 days. The daily growth rates of the hybrid of S. mos-
sambicus x S. niloticus, S. niloticus x S. mossambicus, pure mixed sex
S. niloticus, and pure mixed sex S. mossambicus were 1.16, 0.85, 0.74,
and 0.59 g, respectively. Pruginin (1967) found that the all-male hybrid
produced by crossing S. niloticus x S. hornorum grew 30% faster than mixed
sex fingerlings of S. niloticus and 40% faster than mixed sex fingerlings
of S. hornorum over a 126 day growing period. Lovshin et al. (1977) demon-
strated that there was no statistical difference in the growth rate between the
all-male hybrid of S. niloticus x S. hornorum and male S. niloticus grown
separately and in polyculture with supplementary feeding. The all-male
hybrid grew an average of 1.6 g/day and male S. niloticus, 1.3 g/day. The
all-male hybrid demonstrated an 18% growth advantage over the 180-day
culture period. Dunseth (1977) compared the growth of the S. niloticus x S.
hornorum all-male hybrid, male S. niloticus and male S. aureus grown in
polyculture with channel catfish, grass carp, and silver carp. No statistical
difference was detected between the growth of the 3 male tilapias. However,
the tilapia hybrid grew 7% faster (2.8 glday) than male S. aureus (2.6 g/day)
and 14% faster than male S. niloticus (2.4 g/day) over 160 days.
Pruginin et al. (1975) were unable to demonstrate a difference in growth
rate between the hybrids of S. niloticus x S. aureus, S. vulcani (S. niloticus)
x S. aureus and their parents. Yashouv and Halevy (1967) did not find a
significant difference in growth between the S. niloticus x S. aureus hybrid
and pure S. aureus.
Hulata (pers. comm.) compared the growth of three tilapia hybrids
grown in polyculture with carp. The S. niloticus x S. hornorum all-male
hybrid, S. mossambicus x S. hornorum all-male hybrid, and the S. niloticus
x S. aureus hybrid (70% males) were stocked into earthen ponds with mirror
carp (var. of Cyprinus carpio) and cultured for 105 days. The S. niloticus