Effects Of Dietary Protein Levels On Digestive Enzymes,Non-specific Immunity And Intestinal Contents Bacteria Of Trachinotus Ovatus (Linn)

A30-day feeding trail was conducted to evaluate effects of dietary protein levels on body composition, digestive enzyme activities, non-specific immunity parameters and intestinal bacteria of golden pompano (Trachinotus ovatus, Linn). Three isoenergetic and isolipid (8%) experimental diets with fish meal and soybean meal as protein source and fish oil as lipid source were formulated to contain different protein levels (38%,41%and44%). Each diet was randomly fed to triplicate groups of fish with initial weight of518.81±15.99g. Fish fed three graded diets were labeled as group A, B and C. The main results are as follows:1. Effects of dietary protein levels on body composition of Trachinotus ovatusThe contents of the protein, amino acids, lipid and lipid acids in muscle of Trachinotus ovatus were not influenced by the dietary protein levels. With the increasing of deitary protein levels, contents of muscular protein and amino acids showed slightly increasing tendencies. The protein and total amino acids contents of muscle of each group fluctuated between19.6-20.0%and187-204g/kg respectively. Contents of muscular lipid, saturated fatty acids and unsaturated fatty acids slightly varied from11.0to12.2%,4.1to4.5%and6.9to7.7%respectively with increasing dietary protein levels.2. Effects of dietary protein levels on digestive enzyme of Trachinotus ovatusDietary protein levels significantly influenced the hepatic and intestinal trypsin and pepsin activities (P<0.05) of Trachinotus ovatus. The variation ranges of these two proteolytic enzymes in intestinal, gill, liver and muscle were584.90-9185.84U/mg prot and4.79-42.34U/mg prot respectively. Dietary protein levels has no significant effects on activities of lipase, amylase and cellulose of intestinal, gill, liver and muscle of Trachinotus ovatus (P<0.05). Activities of lipase, amylase and cellulose of tissues and organs varied from37.97to312.35U/mg prot,0.15to0.51U/mg prot and0.25to9.13U/mg prot respectively. In this study, the activities of all digestive enzymes had significant differences among different tissues and organs (P<0.05). Digestive enzymes activities of Trachinotus ovatus showed foregut>midgut>hindgut>liver except cellulose. Results indicated that foregut was the primary region of dietary protein digestion in Trachinotus ovatus digestive tract. Increasing the level of dietary protein would facilitate the protein digestive ability of Trachinotus ovatus.3. Effects of dietary protein levels on the parameters of non-specific immunity of Trachinotus ovatusSerum lysozyme activities of Trachinotus ovatus of three groups were significantly increased and then decreased with the increase of dietary protein levels (P<0.05). Highest lysozyme activity which occurred in group B was17.65U/mg prot. Alkaline phosphatase (AKP), acid phosphatase (ACP) and glutathione peroxidase (GPx) of all tissues and organs in Trachinotus ovatus were significantly increased and then decreased with increasing dietary protein levels (P<0.05). Highest AKP and ACP activities occurred in intestine of Trachinotus ovatus in group B were10056.14U/mg prot and6633.06U/mg prot. Highest GPx activity occurred in liver of Trachinotus ovatus in group B was593.87U/mg prot. The activities of superoxide dismutase (SOD) and catalase (CAT) and total antioxidant capacity (T-AOC) were significantly increased with increasing dietary protein levels (P<0.05). The highest SOD and CAT activities and T-AOC in liver were332.16U/mg prot,42.18U/mg prot and78.40U/mg prot respectively. Malondialdehyde (MDA) contents in all tissues and organs significantly negatively correlated with increasing dietary protein levels (P<0.05). The malondialdehyde content in muscle of Trachinotus ovatus in group B was the lowest with a value of0.48nmol/mg prot. The results indicated that the non-specific immunity would be enhanced when fed Trachinotus ovatus with dietary protein41%.4. Effects of dietary protein levels on bacteria in intestinal contents of Trachinotus ovatusPCR-DGGE, a technology of molecular ecology, was used to investigated differences of bacteria in intestinal contents of Trachinotus ovatus fed dietaries with different protein levels. Analysis of PCR-DGGE fingerprint indicated that bacteria community in hindgut contents of Trachinotus ovatus in group B had the highest diversity with a value of3.156. Bacteria community of foregut contents of Trachinotus ovatus in group B had the lowest diversity with a diverse value of2.732. Similarity analysis indicated that bacteria community of midgut and hindgut of Trachinotus ovatus in group C were the most similar with a similarity coefficient of50%. Bacteria communities of midgut of Trachinotus ovatus in group B and group C were the most different with a similarity coefficient of37.14%. The clustering analysis indicated that bacteria communities of different intestinal segments of Trachinotus ovatus in group C showed furthest distances which meant diet contain44%protein influenced the intestinal bacteria community structure of Trachinotus ovatus mostly. The sequencing results of bands cut from DGGE gels showed that dominant bacteria of Trachinotus ovatus intestine mainly belonged to Proteobacteria, Firmicutes and Chloroflexi.