Survival rate
The variables ‘season’, ‘C. carpio stocking weight’and
‘stocking density’were, next to‘wild ¢sh biomass’, included
in the survival rate multiple regression.Wild
¢sh bene¢t from the modi¢cations made to the rice
¢eld and the speci¢c rice^¢sh management (Rothuis
et al.1998c). In our experiments, the predator Channa
striata (Bloch) was the main wild ¢sh species. This
species is known to predate on C. carpio (Alikunhi
1966).While we tried to prevent entry of wild ¢sh in
our experimental ¢elds, we found wild ¢sh in nearly
all plots at harvest. Whereas Rothuis et al. (1998c)
postulated that these apparently have no adverse effect
on the yield of introduced ¢sh, the data presented in this paper (Table 6) and byVromant et al. (2002a)
for O. niloticus and by Vromant et al. (2002b) for B.
gonionotus seem to prove otherwise.