AMINO ACIDS AS FEEDING STIMULANT IN THE DEVELOPMENT OF SOYBEAN-BASED DIET FOR JUVENILE GROUPER Epinephelus fuscoguttatus

Groupers are popular species for the mariculture industry especially in the Southeast Asian region. As groupers require diets with high protein level for optimum growth, farmers have to rely on the expensive fish meal (FM) based-compounded feeds to farm groupers. Therefore, many researches have been carried out to find the suitable alternative protein sources to substitute FM in the practical diets for groupers. Many studies have proven that soybean meal (SBM) protein indeed is the best candidate among the plant-based proteins, to partially replace the FM protein in the diets for juvenile groupers. However, high dietary inclusion levels of SBM protein generally will reduce the diets palatability and causes poor intake and fish growth. Supplementation of suitable dietary feeding stimulants (FS) can be practiced to solve this problem but there is still limited information on the suitable FS for groupers. Amino acids are the commonly known FS for fish. The taste preference in fish for amino acids is species-specific. Therefore in the present study, behavioral assays were conducted through video recording to identify the amino acids which are preferable by the juvenile grouper Epinephelus fuscoguttatus, and an 8-week feeding trial was conducted to evaluate the potential of the selected amino acids as FS for the fish.   

In the behavioral assays, juvenile E. fuscoguttatus with the average body weight (BW) at approximately 22.9 g was used. Agar gel pellet was used as the medium to deliver 19 amino acids to the fish. The pure agar gel (PAG) and feed extract (FE) pellets were used as the negative- and positive-control, respectively. From the recorded videos, two parameters were observed: (I) the pellet was consumed or rejected [A] - if consumed, recorded 1; if rejected, recorded 0, and (II) frequency of the pellet been captured before it was consumed or rejected and ignored [B], and the preference index was calculated through [A] /[B]. The PAG pellet was totally rejected by the fish (index's value = 0). Among the 18 amino acids tested, only 6 amino acids were found acceptable to fish (index's value ranged from 0.07 to 1.00). These selected amino acids were then supplemented (1.0%) into the soybean meal (SBM)-based diet (40% fish meal protein replaced with SBM protein) to evaluate its potential to improve the feed intake of the SBM diet in the juvenile E. fuscoguttatus (average BW 15.6 g).

Through the feeding trial, it was determined that the dietary supplementation of the selected amino acids has significantly improved (P < 0.05) the feed intake of SBM diet by the fish (Fig. 1). In addition, fish fed SBM diet with the AAM supplementation (AAM10) attained higher weight gain and specific growth rate than those without the supplementation but no significant difference was found. Although the feed intake, weight gain and specific growth rate of fish fed AAM10 were not comparable to those fed with the control (FM-based) diet, the positive effective of the AAM as feeding stimulant for grouper was confirmed.