POLYCULTURE OF SIX FISH SPECIES UNDER DIFFERENT MANAGEMENT SYSTEMS IN EGYPT.

POLYCULTURE OF SIX FISH SPECIES UNDER DIFFERENT MANAGEMENT SYSTEMS IN EGYPT.
By
EL-SERAFY,* 5.5.; A.A. EL-GAMAL; A.S. AL-ZAHABY AND G. ABDEL- NASSER
* Faculty Of Science, Zagazig University, Benha Branch, Egypt.
Key Words: Poly culture, Fish culture, Multiple fish Harvesting.
ABSTRACT
A polyculture Combination of silver carp, HIPophthalmichthys
molitirl; common carp, Cyprinus carpio, bighead carp; Aristichthys
nobilis, grass carp, Ctenopharynqodon idella; mullet, Muqil cephalus
and tilapia, Oreochromis niloticus at stocking densities of 1488,
1488, 571, 714, 2620 and 3119 fingerlings per hectar, respectively was
examined through two successive durations of cultivation, namely short
duration and long duration of 7 &19 months respectively. In the short
duration, the net production was 1851 kg/hectar and the food
conversion ratio was estimated as 3.19. The net productlon for the
long duration was 5050 kg/hectar and the food conversion ratlo was
found as 3.42.
On the other hand, fish production in the polyculture system uSlng
multiple harvesting technique was evaluated over the same above
mentioned periods. The net production during the short term culture
(7 months) was 1934 kg/ha at a survival rate of 94.8 \ and a food
conversion ratio of 3.05. While, it was 6498 kg/ha for the long term
culture (19 months) at a survival rate of 89.5 \ and a food conversion
of 2.14.
Some fish species such as silver carp and common carp reached near
the maximum carrying capacity in shorter time than that for the other
fish species.
Intraspecific competition -among large carps and their progeny from
the wild spawning and lnterspeclflc competitlon between carps and
mullet sharing the same ecological niche -decreased the growth rate of
common carp where natural food was not sufficlent.