The Biology and Culture of Tilapias

5,000 all-male tilapia treatments, respectively. The corresponding tilapia
productions were 2,224, 3,045, and 3,327 kg/ha with average weights
of 770, 725 and 702 g and the total average productions were 9,677'10,246
and 11,106 kg/ha. The FCR's for combined tambaqui and tilapia production
were 3.4, 3.2 and 2.9. Increasing the stocking rates of the tilapia hybrid
therefore increased the total fish production per pond without significantly
affecting the growth or production of tambaqui. A summary of research
results performed with tambaqui and the all-male tilapia hybrid can be found
in Table 3.

Miscellaneous Aspects

COLDTO TOLERANCE

Chervinski and Lahav (1976) demonstrated that S. aureus native to
Israel was more cold tolerant than S. niloticus introduced from Africa.
The hybrid produced by crossing S. niloticus x S. aureus was as cold tolerant
as S. aureus. S. aureus and the S. niloticus x S. aureus hybrid began dying
at 9°C while S. niloticus died at 11°C.
Lee (1979) tested the cold tolerance of S. aureus, S. niloticus, S. horno-
rum, and their hybrids. All fish tested were acclimated to 21°C and the
temperature was decreased about O.S°C/hr until 50% mortality was recorded.
For the purebred fish, S. aureus had the lowest thermal tolerance limit
(6.7"C) and S. hornorum the worst (10°C). The cold tolerance limits of
hybrids of S. aureus x S. niloticus were not significantly different (P > 0.05)
from the pure S. aureus but they were significantly more cold tolerant than
pure S. niloticus and the S. niloticus x S. hornorum hybrid. These results
suggest that cold tolerance is a specific attribute of S. aureus and is probably
transmitted to its hybrids.

Lovshin et al. (1977) mentioned that the S. niloticus x S. hornorum
all-male hybrid is easy to seine like its male parent S. hornorum, whereas
S. niloticus is very difficult to seine and lies on its side in the bottom mud as
the seine passes over.
Dunseth (1977) tested the catchability of male S. aureus, male S. niloticus,
and the S. niloticus x S. hornorum all-male hybrid in replicated seine trials in
400 m2 ponds. An average of 2% of the populations of male S. niloticus and
S. aureus could be caught in the first seine haul. However, 50% of the
all-male hybrid population was caught in the first seine haul.

Discussion

Fingerling production is a major constraint to commercial culture of

tilapia hybrids, especially where 90 to 100% males are required. Maintain-