| Feeding trials were conducted to investigate the effects of dietary corn gluten meal(CGM) on growth, digestion and protein metabolism in relation to IGF-I and TORgene expression of Japanese seabass, Lateolabrax japonicas; the optimumrequirement of dietary lysine for Japanese seabass (initial body weight215.00±3.00g).The results of the present study were presented as follows:1. Effects of dietary corn gluten meal on growth, digestion and proteinmetabolism om relation to gene expression of Japanese seabass, LateolabraxjaponicusA60-day feeding trial in seawater floating cages (1.5×1.5×2.0m) wasconducted to investigate the effects of dietary corn gluten meal (CGM) levels on feedintake, growth performance, survival, digestion and protein metabolism in relation togene expression of Japanese seabass (initial body weight18.09±0.10g). Sixisonitrogenous (crude protein43%) and isoenergetic (18kJg1) practical diets wereformulated by replacing0(the control),15,30,45,60and75%fish meal protein withCGM protein. Each diet was randomly fed to triplicate groups of fish, and each cagewas stocked with30fish. Fish were fed twice daily (05:30and16:30) to apparentsatiation. The survival rate ranged from96to100%, and no significant difference wasobserved among dietary treatments (P>0.05). With increasing dietary CGM levels,feed intake (FI) and specific growth rate (SGR) decreased, however, feed efficiency(FE) had an opposite variation trend. Fish fed the diet with75%protein from CGMhad significantly lower SGR than the control group (P<0.05), and FI wassignificantly lower compared with the control group (P<0.05) with a60%substitutionlevel. Apparent digestibility coefficient (ADC) of protein significantly decreased infish fed diets with75%protein from CGM compared with the control group (P<0.05),but ADCs of lipid and phosphorus both increased with increasing dietary CGM levels,while ADC of dry matter (DM) showed no significant difference among dietary treatments. There were no significant differences in activities of digestive enzymesamong dietary treatments (P>0.05). When the substitution level was equal to or above15%, the activities of protein metabolism enzymes (alanine aminotransferase, ALT;aspartate aminotransferase, AST) were significantly lower compared with the controlgroup (P<0.05). Hepatic insulin-like growth factor I (IGF-I) gene expression levelsignificantly decreased in fish fed the diet with60%protein from CGM comparedwith the control group (P<0.05), but no significant difference was observed in IGF-Iexpression level in dorsal muscle. The target of rapamycin (TOR) expression levels inliver and dorasal muscle of Japanese seabass showed no significant difference amongdietary treatments (P>0.05). Results of the present study suggested that protein fromCGM could substitute up to60%fish meal protein without influencing the growth ofJapanese seabass. Dietary CGM level had no significant influnce on TOR signalingpathway, and may affect fish growth by reglulating FI, digestive and absorptive abilityand hepatic IGF-I gene epression level.2. Dietary lysine requirement of Japanese seabass, Lateolabrax japonicusA60-day feeding trial in seawater floating cages (1.5×1.5×2.0m) was conductedto investigate the optimum lysine requirement of Japanese seabass (initial bodyweight215.00±3.00g). Six isonitrogenous (crude protein44%) and isoenergetic(19.59kJg1) practical diets with gradient levels of lysine (1.55,2.16,2.68,3.24,3.70and4.26%DM) were formulated with fish meal, soybean meal, corn gluten meal andyeast meal as the protein source, fish oil, soybean oil and lecithin as the lipid sourceand wheat meal as the carbohydrate source. Crystalline amino acids weresupplemented to meet the essential amino acid requirements based on the whole-bodyamino acid composition of Japanese seabass. Each diet was randomly fed to triplicategroups of fish, and each cage was stocked with20fish. Fish were fed twice daily(05:30and16:30) to apparent satiation. The results showed that dietary lysine levelhad no significant influence on survival rate of Japanese seabass, which was all above95.8%(P>0.05). No significant difference of feed intake was observed among dietarytreatments (P>0.05). With increasing dietary lysine level, SGR and FER of Japaneseseabss all increased first and then kept steady. The optmum lysine requirement of Japanese seabss based on SGR and FER was2.68%and2.47%(%DM), respectivey.No significant difference of viscerosomatic index and hepatosomatic index wasobserved among dietary treatments (P>0.05). With increasing dietary lysine level,whole-body protein content of Japanese seabass increased first and then kept steady,and when dietary lysine level was2.68%(%DM) and above, whole-body proteincontent was significantly higher compared with the contro l group (P<0.05), whilethere was no significant difference in whole-body lipid, moisture and ash contentamong dietary treatments (P>0.05). The activities of hepatic AST and ALT firstincreased and then decreased with increasing dietary lysine level, and the maximumvalue was observed when dietary level was3.24%(%DM). |
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