Effects Of Protein Hydrolysates On Growth Performance And Related Gene Expression Of Juvenile Turbot(scophthalmus Maximus L.)

Turbot(Scophthalmus maximus L.) as an important marine carnivorous fish in Chinawas widely farmed. Thisstudy was conducted toinvestigate the effect of dietary protein hydrolysateson growth performance and related gene expression of turbot. Running water culture was used in the experiment,water temperature ranged from 14 to 16℃, salinity was from 30 to 31‰, p H was from 7.5 to 8.0,DO(dissolved oxygen) content was above7 mg/L. The results and conclusion are summarized as follows:1. This experiment was conducted to investigate the effects of small molecular weight of fish protein hydrolysate on growth performance and the expression levels of insulin-like growth factor I receptor(IGF-IR) m RNA in liver of juvenile turbot(Scophthalmus maximus L.)(4.16±0.01g). Four groups of diets were formulated to be isonitrogenous and isoenergetic. Fish protein hydrolysate respectively replaced 0%(UF-0), 5%(UF-5), 10%(UF-10), and 20%(UF-20) of the total protein. The growth experiment lasted for 12 weeks. The results showed that the weight gain rate and specific growth rate of fish fed with UF-0, UF-5 and UF-10 were not significantly different(P>0.05), but were significantly higher than that fed UF-20(P<0.05). There were no significant difference between feeding rate fed UF-0 and UF-5(P>0.05), but significantly lower than that of UF-10 and UF-20(P<0.05). Feed efficiency ratio, protein efficiency ratio and protein retention efficiency of UF-0 and UF-5 were significantly higher than that fed UF-10 and UF-20 groups(P<0.05), and UF-10 was significantly higher than that fed UF-20(P<0.05). Crude protein and crude lipid contents of fish fed with UF-0, UF-5 and UF-10 had no significant difference(P>0.05), but were higher than that fed UF-20(P<0.05). The muscle essential amino acid content, essential amino acid and non-essential amino acid ratio of UF-5 was higher than the other three groups(P<0.05). Liver insulin-like growth factor I receptor(IGF-IR) m RNA expression rose with the increase of fish protein hydrolysate and was significantly higher in fish fed with UF-20 diet than the other three diets(P<0.05). The results indicated that low content small molecular weight compounds from fish protein hydrolysate showed a positive effect on growth and feed utilization in juvenile turbot. High levels of small molecular weight of fish protein hydrolysate would restrain the growth performance. Dietary low content fish protein hydrolysate could improve liver IGF-IR m RNA expression in juvenile turbot.2. This experiment using two homemade fish protein hydrolysates(FPH) and commercial chicken protein hydrolysate to replace 10% total protein and designed four isonitrogenous and isoenergetic diets: the control group(FM), PHa(FPH were hydrolyzed by Flavourzyme and Alcalase), PHb(FPH were hydrolyzed by protamex), PHc(chicken protein hydrolysate).Juvenile turbot(Scophthalmus maximus L.)(4.16±0.01g) were fed with these four diets 12 weeks. Results of this study indicated that the best overall growth and feed utilization of turbot juveniles were fed FM and PHa, and these two groups had no significant difference(P>0.05).The weight gain rate and specific growth rate significantly depressed at fed PHb and PHc compared to the control diet(P<0.05), while no significant difference was observed at fed PHa(P>0.05). There was nosignificantdifference in feeding rate(P>0.05). The feed efficiency ratio, protein efficiency ratio and protein retention efficiency were significantly depressed at PHc group(P<0.05), while there were no difference among PHa, PHb and FM(P>0.05). PHa, PHb and PHc had higher crude protein than FM(P<0.05), while had no significant difference in crude lipid(P>0.05). PHa, PHb and PHc had higher essential amino acid content than FM(P<0.05); EAA/TAA and EAA/NEAA fed PHa, PHbwere higher than FM and PHc, and significantly higher than fed FM(P<0.05). The plica height in foregut and midgut of fed PHa, PHb,PHc were higher than FM, PHa had significant difference with FM(P<0.05), while the intestinal wall thickness fed FM was higher than the other three groups, and significantly higher than fed PHa(P<0.05). These results indicated that the growth response and feed utilization fed PHa and PHb were superior to PHc, and PHa was better than PHb, suggesting that replaced fish meal by moderate FPH in high plant protein diets had no negative effect on juvenile turbot.3. Juvenile turbot(Scophthalmus maximus L.)(7.94±0.10g) were fed 10 weeks with five isonitrogenous and isoenergetic diets which were formulated by replacing0(the control, PH-0) and 10% of fish meal protein with four protein hydrolysates(PH; fish, PH-A; yeast, PH-B; pig blood, PH-C; soybean meal, PH-D). Results showed that the best growth and feed utilization of turbot juveniles were fed PH-0 and PH-A, the weight gain rate and specific growth rate significant depressed at fed PH-B, PH-C and PH-D(P<0.05); there were no difference in feed efficiency ratio, protein efficiency ratio and protein retention efficiency among PH-0, PH-A, PH-B(P>0.05), but significantly higher than PH-C, PH-D(P<0.05). Viscerosomatic index(VSI) and condition factor(CF) were similar among five groups, while fish fed PH-B and PH-C had significantly higher hepatosomatic index(HSI) thanthe other dietary treatments(P<0.05).There were no significant difference among the five groups of digestive enzyme trypsase and amylase activities(P>0.05), GOT and GPT activities in serum of PH-B were significantly lower than other groups(P<0.05). IGF-I gene expression in liver in PH-A, PH-B was significantly higher than the PH-C, PH-D groups(P<0.05). Under this experimental condition, adding the four protein hydrolysates, the growth and feed utilization was the best in fish protein hydrolysate(PH-A), the second was the yeast protein hydrolysate(PH-B), while soybean meal protein hydrolysate(PH-D)was the worst.