Effects of different modified diets on growth, digestive enzyme activities and muscle compositions in juvenile Siamese fighting fish (Betta splendens Regan, 1910)

The effects of four modified diets (gamma-irradiated, microwave-irradiated, probiotic-supplemented and carbohydrase-supplemented diets) were studied on digestive enzyme specific activities and growth performance quality of juvenile Siamese fighting fish (Betta splendens Regan, 1910) during 2 weeks of critical and intensive rearing period. The modified procedures did not change biochemical compositions and gross energy of diets, but generally resulted in relatively higher in vitro digestibilities of protein and carbohydrate and fish survival rate, albeit insignificant. Only gamma irradiation significantly increased in vitro protein digestibility of the diet, and microwave irradiation increased starch gelatinization and water solubility (P < 0.05). Fish fed microwave-treated diet showed highest values in all studied growth indicators and digestive enzyme specific activities (except lipase), with significantly higher amylase specific activity and activity ratio of amylase to trypsin (A/T ratio). Correlation analysis indicated significant relationships (P < 0.05) among the levels of total protease, amylase and trypsin, and between SGR and A/T ratio. Muscle and body compositions of juveniles fed on microwave- or gamma-irradiated diets were similar to the control, while the juveniles fed on probiotic- or carbohydrase-supplemented diets showed lower protein depositions (P < 0.05). Similar levels of RNA, RNA/Protein ratio, and Protein/Lipid ratio in body and muscle in all dietary groups fed ad libitum suggested that the improved growth performance in juvenile Siamese fighting fish fed on microwave-irradiated diet may not be only due to improved physicochemical properties of the diet but also improved fish consumption rate.

► Fish fed microwave-treated diet showed highest value in all growth indicators.
► Microwave-irradiated diet improves digestibilities of protein and carbohydrate.
► Microwave-irradiated diet increases amylase specific activity and A/T ratio.
► Microwave-irradiated diet improves nutrient quality and fish consumption rate.
► Modifications of diets do not change biochemical compositions.