| The study was conducted to investigate the effects of dietary xylooligosaccharides (XOS) levels on the growth performance, body composition, blood biochemical parameters, resistance against Aeromonas hydrophila, intestinal histology and microflora of the tilapia (Oreochromis niloticus×O.aureus).1. The effects of dietary xylooligosaccharides levels on the growth performance, body composition, blood biochemical parameters and resistance against Aeromonas hydrophila of tilapia. A total of960fishes with an initial weight of (5.09±0.12) g were randomly assigned to6groups with four replicates in each group and40fishes per replicate. The fishes were respectively fed a basal diet and5diets supplemented with200mg/kg,400mg/kg,600mg/kg,800mg/kg and1000mg/kg XOS. The activity of superoxide dismutase (SOD), alkaline phosphatase (AKP), catalyse (CAT) and total protein content (TP) in serum were determined on each2weeks, respectively. At the end of feeding trial, the fish were infected with Aeromonas hydrophila. During96hours of artificial infection, the survival rate (SR) was measured. The results showed that fish fed diets with XOS had higher WGR (weight gain rate) than those of the control group, except the group of200mg/kg, however, there were no significant difference (P>0.05). PER (protein efficiency ratio) in800mg/kg group was significantly higher than that in200mg/kg group (P<0.05), FC in800mg/kg group was significantly lower than that in200mg/kg group (P<0.05). There were no significant difference in the body biochemical composition (P>0.05). At4th week, serum AKP, CAT activity and TP content in the groups fed the diets added with XOS were higher than those in control group, and400mg/kg group had the highest data of all the groups (P<0.05). At6th week, serum SOD, AKP, CAT activity and TP content in400mg/kg group were higher than those in the control group significantly. At8th week, serum SOD activity in the groups fed the diets containing XOS was significantly higher than that in the control. After96hours of infection of Aeromonas hydrophila, SR in the groups with XOS was higher than control group by193.3%～255.8%. The results suggested that dietary XOS showed no significant effects on growth performance and body biochemical composition of the juvenile Tilapia(Oreochromis niloticus×O.aureus), but the blood biochemical parameters were significantly affected by XOS and changed with time on dynamic change, and XOS could improve the resistance against Aeromonas hydrophila.2. The effects of dietary xylooligosaccharides levels on the histology and intestinal microflora of tilapia. The number of intestinal micro flora was measured at every2weeks. Midgut was sampled at4th and8th week for histology analysis. The results showed that at4th and8th week, compared with control group, the folding area and the muscle thickness of the intestine in the groups with XOS were significantly higher (P<0.05). Dietary XOS affected significantly the number of intestinal Bifidobacterium and Lactobacillus. Compared with control group, the number of Bifidobacterium in600and800mg/kg groups was significantly higher at4th week (P<0.05), in400mg/kg and600mg/kg groups significantly higher at6th week (P<0.05). At8th week, the number of Lactobacillus in800mg/kg group was significantly higher than that in the control (P<0.05). The number of E. coli in the groups with XOS tended to decrease with the feeding time going, but the difference was not significant (P>0.05). The results suggested that dietary xylooligosaccharides could improve the intestinal histology and increase the number of intestinal Bifidobacterium and Lactobacillus.3. Using PCR-DGGE technique to study the development of bacterial community in tilapia by XOS. Fishes with an initial weight of (2.41±0.06) g were randomly assigned to4groups with four replicates in each group and30fishes per replicate. The fishes were respectively fed a basal diet and3diets supplemented with400mg/kg,600mg/kg and800mg/kg XOS. Midgut was sampled at0,3th and6th week, after analysis of the intestinal bacteria by PCR-DGGE, the results showed that the microflora in the tilapia intestinal were rich in the diversity. The Pseudomonas was able to maintain colonization in the intestine in each experimental group at3th week, but the Pseudomonas disappeared from the intestinal tract in the groups fed the diets with XOS at6th week. In addition to600mg/kg group at3th week and to400mg/kg group at6th week, the rest of the samples were found out Enterobacteriaceae. The Limnobacte and Klebsiella were found in400mg/kg group at3th week. The Pectobacterium were found in600mg/kg group at3th week. In addition to the control group at6th week, the Pseudoalteromonas were found in each group. The results suggested that the Pseudoalteromonas could be colonized in the gut and XOS could affect the intestinal flora species. |
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