EVALUATION AND PROPOSE THE OPTIMUM LEVEL OF DIETARY FUNCTIONAL FEED ADDITIVES IN JUVENILE OLIVE FLOUNDER Paralichthys olivaceus

The present two experiments were conducted to evaluate and propose the optimum level of the different dietary functional feed additives in olive flounder.  First experiment was conducted to evaluate 7 different functional feed additives in olive flounder fed with the low fishmeal diet formulated according to the other previous experiment. Including a control group, 8 groups of fish with three replicates were randomly distributed in 24 rectangular 35 L tanks (15 fish/tank). Fish averaging 5.26±0.17 g (mean ± SD) were fed 8 experimental diets; a basal diet without feed additive was used as a control (CON), CON + encapsulated sodium butyrate (ESB), CON + gamma-aminobutyric acid (GABA), CON + selenium yeast (SeY), CON + yeast extract nucleotide (YEN), CON + yucca meal (YUM), Song-gang bio stone (SGS) and protease (PRT). After 8 weeks feeding trial, growth performance of fish fed GABA, YEN and SGS diet were significantly higher than those of fish fed CON diet.  Non-specific immune responses of  fish fed GABA, YEN,  and  SGS diets were significantly higher than those of fish fed CON diet.  Growth and immune related gene expression of fish fed GABA, YEN and SGS diets were significantly higher than those of fish fed CON diet. Cumulative survival rates of 7 days bacterial challenge test of fish fed GABA, YEN, YUM, SGS and PRT diets was significantly higher than those of fish fed CON diet. In the second experiment, fish averaging 2.1±0.07 g (mean ± SD) were randomly assigned into 8 groups and fed eight experimental diets; CON diet, and seven other diets supplementing YEN at 2.5 g (YEN_2.5) and 3.5 g (YEN_3.5), SGS at 2.5 g (SGS_2.5) and 3.5 g (SGS_3.5), GABA at 200 mg (GABA₂₀₀) and 250 mg (GABA₂₅₀ ), and oxytetracycline at 4 g (OTC) per kg diet. Growth performance of fish fed YEN_3.5, SGS_2.5, SGS_3.5 and OTC diets were significantly higher than those of fish fed CON diet (P ˂0.05). Non-specific immune responses of fish fed YEN_3.5, SGS_2.5, SGS_3.5 and OTC diets were significantly higher than those of fish fed CON diet. Digestive tract trypsin activity of fish fed YEN_2.5, YEN_3.5 and SGS_3.5 diets were significantly higher than those of fish fed CON diet (P <0.05). Growth and immune related gene expression of fish fed YEN_3.5 and SGS_3.5 diets were significantly higher than those of fish fed CON diet. Intestinal villi length of fish fed YEN_2.5, YEN_3.5, SGS_2.5, SGS_3.5 and OTC diets were significantly higher than those of fish fed CON diet (P˂0.05). Cumulative survival rates of 8 days bacterial challenge test of fish fed YEN_3.5, SGS_3.5 and OTC diets were significantly higher than those of fish fed CON diet. These results indicated that dietary 3.5 g yeast extract nucleotides (YEN_3.5) and 2.5 (SGS_2.5) or 3.5 (SGS_3.5) g Song-gang stone per kg diet could replace antibiotics, and have beneficial effects on growth, immune responses, histology, disease resistance and gene expression in the low fishmeal diet of olive flounder.