Behavioural assays
The behavioural assays started after all fish were successfully conditioned to accept agar gel pellet. Each treatment of TS pellet was fed to 50 replicates of the individual fish. The procedure of the behavioural assays in this study was adopted from that of Kasumyan and Morsi (1996) with modifications. The behavioural assays began by providing a piece of FT pellet to the fish to trigger its feeding desire, followed with a TS pellet, and then another piece of FT pellet. The last piece of FT pellet was served to recover the fish acceptance to agar gel pellet because the fish may be conditioned to reject agar gel pellet if any of the chemical substances tested was a deterrent to the fish. During the behavioural assays, the feeding responses of each fish to the given TS pellet (ingested or rejected) were observed and recorded. If the fish did not show any response to the given TS pellet (the TS pellet was not captured in mouth by the fish), that particular assay was not counted, and it will be repeated the other day. Each TS pellet was tried only once on each fish to avoid adaptation of the fish to the chemical substance tested, and only one test to the fish in each day. The PAG pellet was used as the negative control in the behavioural assay, and it was tested on the fish as the other TS pellets were. After each of the successful assay, the fish was rewarded with the Otohime commercial pellet until apparent satiation level. Tank cleaning was conducted and about 50 % of water in each aquarium was exchanged in the next day at least 4 h before the behavioural assays started. Throughout the experimental period, the water temperature in aquarium ranged from 28 to 29 °C.