The water temperature was relatively stable in both
ponds, ranging from 26 to 32°C during most of the
grow-out period, except during the last month in
December when it decreased to 20-25°C (Fig. 2).
Catfish are sensitive to cool temperatures (< 25°C)
which reduce their feeding activity (Supranee
Chinabut, pers. comm.). It is commonly observed
that catfish stocked during the cool part of the year
often suffer from disease. The relatively great Secchi
disc depth (35-50 cm) in the initial period decreased
rapidly to 20-30 cm during most of the experimental
period, but a considerable difference existed between
the two ponds (Fig. 2). Chlorophyll a concentration,
representing phytoplankton biomass, ranged from 20
to 180 mg/m3, and showed an inverse pattern to that
of Secchi disc I depth. The suspended solids were