Effect Of Different Soluble Pectin And Xylan On Growth, Digestive Physiology And Intestinal Flora Of Chinese Mitten Crab, Eriocheir Sinensis

Non-starch polysaccharides(NSPs) had a high level in plant feed, which was one of the important anti-nutrients. There were many kinds of NSPs, according to the solubility it can be divided into soluble and insoluble NSPs. Livestock and poultry studies had shown that the anti-nutritional effect of NSPs primarily by increasing digesta viscosity which was resulted from soluble NSPs. While the insoluble NSPs would only play the role of a nutrient diluent, which had small negative impact on nutrients digestion and absorption. Aquatic animals living in the water, which had higher the moisture content within the digestive tract and digestive differentitation was not as well developed as livestock and poultry. These two reasons may cause the different response of aquatic animals than livestock and poultry. Chinese mitten crab is an important aquaculture species and pectin and xylan are the highest content of two non-starch polysaccharides in aquaculture feed ingredients. In this study, we use different soluble pectin and xylan as material to investigate its effects on Chinese mitten crab growth, digestive physiology and intestinal micriflora. Designed to reveal the mechanism of anti-nutritional effects of NSPs and provide theoretical support for the improvement of Chinese mitten crab feed formulation.The test pectin and xylan were food grade merchandise. In order to determine the content of the test material NSPs, we analysis the content of soluble and insoluble pectin and xylan in the feed ingredients by gas chromatography firstly; then we made the semi-purified diet which had 12% of merchandise pectin and xylan and analyzed the feed viscosity by using viscometer. On this basis, test diets were fed juvenile Chinese mitten crab, whose initial body weight was(1.6±0.7) g, for 13 weeks. Diet viscosity, special growth rate, feed conversion ratio, energy and nutrients retention, body composition, serum cholesterol and triglyceride, activity of lipase, amylase in hepatopancreas,intestinal morphology and flora structure were measured. Meanwhile, the crabs with an initial body weight(1.56±0.62) g were fed with these four semi-purified diet 8 weeks. The faeces were collected and analyzed the apparent digestion and absorption of nutrients.The experimental results showed that:(1) Soluble pectin had an effective content of 85.9%; Insoluble pectin had an effective content of 81.1%; Soluble xylan had an effective content of 78.8%; Insoluble had an effective content of 88.1%.(2) Dietary viscosity varied greatly, with diet containing SP the highest, followed by diet containing ISP, and diet containing ISX the lowest.(3) No significant difference was observed in special growth rate, body composition and digestive enzyme activity among groups(P>0.05).(4) Feed conversion ratio of group SP was higher than of group ISP and group SX(P<0.05) while no significant difference was detected between group ISX and other groups(P>0.05).(5) Retention of protein, lipid and energy of group SP was lower than that of group ISP(P<0.05), however, protein retention of group SX was higher than group ISX(P<0.05) and no significant difference was detected between group ISP and group SX.(6) No significant difference was observed in serum cholesterol between soluble and insoluble NSPs(P>0.05). However, it was lower in-group ISP than in group SX and ISX(P<0.05).(7) The digestion and absorption ration of DM, protein, fat and energy were significantly lower in-group pectin than that in-group xylan(P<0.05). It had no significant effect on feed digestion and absorption of nutrients between different soluble pectin groups(P>0.05). The digestion and absorption ration of DM, protein and energy was significantly higher in-group SX than that in group ISX(P<0.05), but digestion and absorption ration of fat had no significant difference between them(P>0.05).(8) Peritrophic membrane was observed in various parts of crab intestinal. No significant difference was observed in peritrophic membrane thickness, number of wrinkle wall, wrinkle wall width and height in hindgut of Chinese mitten crab among each group(P>0.05).(9) The intestinal bacteria of Chinese mitten crab were mainly composed of tenericutes, bacteroidetes, firmicutes, proteobacteria and CKC4 these five phylum bacteria. There was no significant difference between group SP and group ISP in intestinal flora diversity and richness(P>0.05), but the difference between group SX and ISX were significant(P>0.05).The results show that the effect of NSPs had effect on the feed nutrient utilization of crab, but the influence mechanism might relevant to the viscosity rather than the soluble. Viscosity too high or too low will reduce crab feed nutrient utilization. NSPs had no significant effect on crab intestinal morphology, it might be related to its specific peritrophic membrane. The effect of pectin on structure of intestinal flora has nothing to do with its soluble, but the effect of xylan on structure of intestinal flora was related to its soluble.