2.4. Fish Preparation. Healthy hybrid catfish (Clarias gariepinus
Male × Clarias macrocephalus Female) were obtained
from local farms in Ubon Ratchathnai Province, Thailand.
To acclimate to laboratory conditions, fish were maintained
in 2m × 2m × 0.6m cement ponds for two weeks prior
to experiments. On the day of stocking, the fish were fed
3% body weight twice a day with the commercial pellet fish
diet for small catfish (Charoen Pokphand Group, Bangkok,
Thailand). Twenty-four h prior to the experiments, fish
weighing 50 ± 1 g were transferred from the stocking ponds
to 180 cm × 60 cm × 60 cm aquaria (20 fish per aquarium).
Aquaria were cleaned every third day by siphoning off twothirds
of water and replacing it with fresh water.