This experiment was conducted to study the mutual effect between fish
and rice in rice fields with inorganic fertilizers. Three different polycultures, P1 (Nile
tilapia + crayfish), P2 (common carp + crayfish) and P3 (Tilapia + carp + crayfish)
were studied with T1 (urea), T2 (superphosphate), T3 (urea + superphosphate), T4
(without fertilizers). Meanwhile, a rice field free from fish was used to compare rice
yield in the experimental treatments. The results showed that water quality measurements were within the
normal ranges and suitable for the experimental fishes. Urea + superphosphate
treatment gave the types of phytoplankton and zooplankton needed by fishes and
consequently gave the highest growth performance of carp and crayfish polyculture.
The whole body composition of tilapia and carp had no clear trend in the different
polycultures or treatments while crayfish was not affected. The rice yield increased
by 9-13% when applying urea + superphosphate while the highest net return was
obtained with superphosphate alone in carp-crayfish polyculture. It could be recommended to raise common crap along with crayfish in rice
fields fertilized with urea + superphosphate. If urea is high in price or unavailable,
superphosphate alone is recommended. This system of production increases the
net return of small farmers under similar conditions by increasing the rice yield
beside the fish yield.