This leads to
direct competition for food among fish species and a
loss of the advantage of polyculture (Hepher,
Milstein, Leventer & Teltsch 1989). In our experiments,
the fish stocking density varied between 0.5
and 2.5 fishm±2 if one calculates the stocking density
as number of fish per `trench + field' area, as is widely
done. However, if one calculates the stocking density
as number of fish per trench area, one obtains a
stocking density varying between 3.33 and 16.5 fish
m±2. It can be argued that the latter should be used
for fish culture in rice fields as the field aquatic
conditions are far from optimal for fish culture
during a substantial part of the rice cropping season.