This study was conducted to determine the acceptability to betaine as a feed enhancer in the brown-marbled grouper, Epinephelus fuscoguttatus at grow-out stage. Different ratios of betaine (BET) + amino acid mixture (AAM) (1:1, 1:2, 1:3, 1:4, 1:5) were delivered to the fish through agar gel pellets in the behavioural assays and the Index of Preference (IndPrf) was calculated. The pure agar gel (PAG) pellet was totally rejected (IndPrf value 0), while the BET and AAM treatments also were not preferred by the fish (0.24 and 0.41, respectively). However, all BET + AAM treatments attained almost perfect IndPrf value (0.83 - 1.0, P>0.05), and were significantly higher (P<0.05) than the PAG, BET, and AAM treatments. In conclusion, the acceptability to betaine as feed enhancer in the E. fuscoguttatus at grow-out stage was very high; small amount of betaine was sufficient to enhance the taste of the AAM.
