O. niloticus is a tropical fish widely grown in Brazilian aquaculture.
The fish used in this experiment, weighing an average of 45 g
(±3 g) were obtained from the Moana Company, Cananéia, SP,
transported to the Fishery Institute in Cananéia and acclimated
for 2 weeks. During this period the fishes were kept in 100 l outdoor
ponds. They were supplied with a continuous flow of water
that was artificially aerated, with temperature controlled to 25–
27 C. Fish were exposed to natural light and fed commercial feed.
Feeding was suspended 24 h before the experiment began to prevent
the accumulation of organic matter in the ponds.