carp, big headed carp, etc. totalling about 200 t. There is a price differential between
small and large tilapia. A 200 g fish costs about $1.20 and the bigger ones about $2.
NASH: Dr. Hepher, can I ask if you tried the same stocking formula for polyculture in
different sized ponds, and do you get the same results operating at say, 1 ha and 'h an
acre.HEPHER: Yes, we do. Once you have prevented wild spawning or uncontrolled repro-
duction, the results are the same irrespective of pond size.LOVSHIN: I would like to suggest another method which I think is valid for raising
tilapias. Dr. Hepher has been talking largely about the Israeli situation, but elsewhere, a
predator to control unwanted recruitment can be very useful if a good native species is
available. In Israel, they do not have a prcdator but there are many places in the tropics
where native predators are available and can be reared easily. This is a good system.HEPHER: I agree. The only problem is that most information on the use of such pre-
dators is from experimental work not commercial culture. I think the main reason is the
great difficulty in obtaining the fry of some of these predators. Take for instance the Nile
perch which when grown in combination with tilapias will prey on the small tilapia.
You cannot get large quantities of Nile perch fry very easily. It will not spawn readily
in ponds. I think though that you have used predators successfully.LOVSHIN: We have used Cichla ocellaris, but mostly for experimental work. The mass
rearing of this species is no problem. I do know also of small scale commercial use of a
Cichlasoma sp. in El Salvador.MIRES: What is its native name?LOVSHIN : It is a cichlid. Cichlasoma managuense.
HEPHER: Although it has not been used commercially, I can give you another example
of a good predator-the seabass species, Dicentrarchus labrax, or D. punctatus. Again, you
face the same problem. They are wonderful fi, but you cannot get the fry.LOVSHIN: In Taiwan, I know that the , snakehead Channa striata is used commercially.
They reproduce it and they put it in the tilapia ponds, and it works well as a controlling
predator. What I am saying is that there are some commercial examples; not as much as
the use of monosex culture, but still enough to indicate a valid system. I think as tilapia
culture expands, we are going to see more and more use made of predators.HEPHER: I agree.PULLIN: In the Philippines, the ICLARM and Central Luzon State University cooperative
project on integrated animal-fish culture uses snakehead as a controlling predator for
tilapia culture in manured ponds. We have found, however, that simple predator:prey
ratios are not adequate as management guidelines for different lengths of culture period.
You have to adjust to the different recruitment loads.LOWE-MCCONNELL- Dr. Hepher, is sexing done by eye, because I know that some
tilapias are much more difficult to sex than Sarotherodon mossambicus?HEPHER: We do not sex Sarotherodon mossambicus, but we do sex S. aureus and
hybrids. It is quite easy. At Dor, all we have is about a 3 to 4% error. It should be done
when the fish are over 50 g because then the differences are more marked.GUERRERO: In the Philippines, we are experimenting with polyculture of tilapias with
invertebrates, with freshwater shrimps and prawns. We think there is commercial potential
for these systems, particularly in developing countries.
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