Fish management implications
Rothuis et al. (1998a) argued that there is no advantage
of culturing O. niloticus and C. carpio together in
rice ¢elds. However, Vromant et al. (2002a) argued
that this would be possible provided that the ¢sh are
stocked at low densities and that the trench of the
rice^¢sh ¢eld is manured or fertilized. The data presented
in this paper show that there is interspeci-
¢c competition between C. carpio and O. niloticus.
Furthermore, increasing the feed or nutrient availability
in the rice ¢eld £oodwater has a positive impact
on O. niloticus (Vromant et al. 2002a), but not on
C. carpio growth. Fromthis, we conclude that when it
is impossible for farmers to increase the feed or nutrient
availability in the aquatic environment, either C.
carpio or O. niloticus could be stocked. However,when
fertilizer or manure can be added to the trench or
when extra food can be given to ¢sh, O. niloticus
seems more appropriate than C. carpio. To obtain
higher survival rates, farmers should stock fewer ¢sh
but of a larger size. Stocking in the wet season ismore
appropriate than stocking in the dry season, but only
after thorough eradication of wild ¢sh species.