former, males can kill females or cause ovarian regression by repeated
attacks, whereas in ponds, the females have space for escape and are rarely
adversely affected. Mr. Mires described aquarium observations in which ripe
females were keen to enter the males' breeding territories and the males
pushed and encouraged them to enter. If this also occurs in ponds with a
preponderance of males, it means that ripe females are continually beom-
barded by courting males. This could have a stirnulatory effect and help t~
account for the good results of hybrid crosses with 'male pressure'. The
question of breeding coloration was raised but it was felt that this had little
relevance in ponds, where visibility was often very low.
The discussion centered first on the possible alternatives to spawning
ponds for mass fry and fingerling production. The example of mass fry
production using cages (hapas) was described by Dr. Guerrero. Prof. Roberts
commented that a commercial farm in Kenya was producing large numbers
of pure strain, hybrid and sex-reversed tilapia fry for sale within Kenya,
Nigeria, other African countries and the Middle East. Details of the system
used were not available.
Dr. Philippart mentioned that an experimental system of 4m2 fiberglass
tanks had also been developed using recirculated heated effluents in Belgium.
The system, with 15 to 16 spawnersltank produces about 500 fryltanklday
for short periods (5 to 7 days) of intense reproductive activity and about
150 fryltanklday on average over longer periods (50 days). Small females of
around 100 g perform better than larger fish. The development of intensive
recirculatory raceway systems for fry production was discussed but it was
felt that these would be costly both in construction and energy requirements.
It was agreed that most of the large-scale commercial production of
tilapia fry was still done in spawning ponds. Mr. Mires stated that in Israel,
producers have changed from small to large spawning ponds because the
demands of buyers were constantly changing with respect to size and num-
bers of fish. Large spawning ponds become essentially early nursery ponds as
well. Fry or fingerlings can be harvested and graded to meet demands with
less labor and management than from numerous small ponds. At the Kibbutz
Ein Hamifrats hatchery, the use of large spawning ponds has reduced the
monthly labor requirement for frylfingerling harvest to four hours work by a
team of five to six people.
The development of tilapia hatcheries was felt to be the key to expansion
of the culture industry. A small number of large'hatcheries with well-trained
personnel was considered to be a better prospect than large numbers of
hatcheries scattered throughout the rural areas of developing countries. This
would allow controlled production of good strains, hybrids, etc. It was
recognized, however, that distribution difficulties could arise in island
systems like the Philippines and in areas where roads and communication
systems are very poor and fuel prices high. In these cases, local hatcheries
would be essential. Tilapias are among the hardiest of fish and survive
transportation very well. Prof. Roberts commented that tilapia fry brought