The Effects Of Pectin And Xylan On Growth, Digestion And Intestinal Flora In Chinese Mitten Crab (Eriocheir Sinensis) And Yellow Catfish (Pelteobagrus Fulvidraco)

Pectin and xylan are two main types of non-starch polysaccharides (NSP) inplant-based feedstuffs. Fish and other monogastric animals do not have the ability ofdigesting and utilizing NSP for lacking of relevant enzymes. A lot of research conductedon livestock and poultry suggested that NSP had a negative effect on the function ofintestinal and the digestion and absorption of nutrient substance, and reduce animalgrowth performance, especially the soluble NSP. The digestive tracts of Eriocheirsinensis and Pelteobagrus fulvidraco are relatively short and have low degree ofdifferentiation. The effect of pectin and xylan on digestive function of these two animalshas not been reported. This experiment was conducted to study the effect of pectin andxylan on the growth, digestion, and intestinal flora of these two aquatic animals,building up research data of these two aquatic animals on the nutrition physiology ofNSP, and provides a reference for feed formulation optimization as well.In test one,8%pection and30%wheat bran (xylan, including1.67%soluble xylanand10.98%wheat bran total xylan) were added into the diets respectively. In controldiet, pectin and wheat bran were degradated by pectinase (diet P-ED) and xylanase (dietX-ED) respectively before utilization (The former had4.69%pectin, and the latter has0.93%soluble xylan and9.48%wheat bran total xylan). The semipurified diets in allgroups were isonitrogenous（CP36%）and isolipid (EE6%). Crabs with initial bodyweight of (5.9±0.4) g and fish with initial body weight of (23.5±1.7) g in concretepond were fed for8weeks in three replication, then the growth rate, body compositionand blood lipid level were determined. Meanwhile, crabs with initial body weight of (42±5.1) g and fish with initial body weight of (52.3±7.5) g in aquarium were fed on thesemipurified diets for8weeks to analyze the digestive enzyme activity and the apparentdigestibility of nutrients.Results from Eriocheir sinensis suggested that:(1) The weight gain rate, specific growth rate and hepatopancreas index of E. sinensis in test groups had no obviousdifference with the control group (P>0.05).(2) The moisture of crabs in xylan groupwere significantly more than its control (P<0.05), however, no significant differencewere observed in crude protein, crude fat and crude ash in both test groups (P>0.05).(3)The serum cholesterol, low density lipoprotein (LDL) and alkaline phosphatase (AKP)activity of pectin group were significantly lower than its control group (P<0.05), and theblood sugar content was significantly higher than its control group (P<0.05).(4) Theprotease activity and lipase activity of hepatopancreas in two test groups had no obviousdifference with their corresponding controls (P>0.05), but the amylase activity ofhepatopancreas in two test groups were significantly lower than their correspondingcontrols (P<0.05).(5) The dry matter digestion and fat digestibility of pectin group weresignificantly lower than its control group (P<0.05), and the fat digestibility of xylangroup were significantly lower than its control group (P<0.05). The differences ofprotein digestibility were not significantly (P>0.05).(6) The peritrophic membrane wasfound in the guts of E. sinensis, which separate the intestinal epithelium from the chime.The fold width in hindgut of E. sinensis of pectin group were significantly lower than itscontrol group (P<0.05). No significant difference was observed in the number, height,widthth of fold and the thickness of the muscular layer (P>0.05). The intestinemorphology of xylan group had no obvious difference with its control (P>0.05).The experiments of Pelteobagrus fulvidraco showed that:(1) The specific growthrates, protein accumulation and lipid accumulation rates in both test groups weresignificantly lower than their control respectively (P<0.05). However, no significantdifference was noticed in food coefficient and feeding rate (P>0.05).(2) The conditioncoefficient in xylan group were significantly higher than its control (P<0.05), and theindex of the gastrointestinal tract was significantly higher than its control group(P<0.05). The visceral index and hepatopancreas index of the two test groups showedno obvious difference with their own control groups (P>0.05).(3) The moisture content,body and muscle lipid content of the whole fish in pectin group were significantly lowerthan its control (P<0.05). Similarly, the body and muscle lipid content in xylan groupwere significantly lower than its control (P<0.05). The ash content of whole fish inxylan group were significantly higher than its control (P<0.05).(4) The serum contentof total cholesterol, high-density lipoprotein and low-density lipoprotein in pectin groupwere significantly lower than its control (P<0.05). The serum total bile acids, total cholesterol serum, high-density lipoprotein and low-density lipoprotein in xylan groupwere significantly lower than its control (P<0.05). No significant difference wasdetected in serum triglycerides and blood glucose (P>0.05).(5) The intestinal proteaseand lipase activity in pectin group were significantly lower than its control (P<0.05).And the lipase and amylase activity in xylan group were significantly lower than itscontrol (P<0.05).(6) The digestibility of dry matter, protein and fat in pectin group wassignificantly lower than its control (P<0.05). The fat digestibility in xylan group weresignificantly lower than its control (P<0.05), however, no difference was observed indigestibility of dry matter or protein (P>0.05).(7) The height as well as width ofintestinal mucosal folds and the thickness of the muscular layer in pectin group weresignificantly lower than its control (P<0.05). The width of intestinal mucosal folds,, thethickness of submucosa and muscular layer in xylan group were significantly lower thanits control (P<0.05).In experiment two, fish with initial body weight of (23.5±1.7) g and crabs withinitial body weight of (5.9±0.4) g were fed on four kinds of semi-purified diets for8weeks. Then guts of fish and crabs were isolated under sterile conditions, and theintestinal flora was analyzed through454pyrosequencing. The results showed that inthe intestinal flora of Eriocheir sinensis there were five kinds of bacteria belong todifferent phyla, including Tenericutes, Proteobacteria, CK-1C4-19, Firmicutes, andBacteroidetes. The microbial diversity of crab intestinal flora of pectin group was higherthan its control. The ratio of harmful bacteria in intestinal flora, such as Proteobacteriaand Bacteroidetes, were reduced compared to its control. The microbial diversity andabundance of intestinal flora of xylan group was higher than its control. The ratio ofprobiotics to intestinal flora, like Firmicutes, was higher than its control.In the intestinal flora of Pelteobagrus fulvidraco, there were four kinds of bacteriabelong to different phyla, including Proteobacteria, Fusobacteria, Firmicutes,Bacteroidetes. The microbial diversity and abundance of fish intestinal flora in pectingroup was higher than its control. The ratio of Proteobacteria to intestinal flora wasincreased compared to its control, and the abundance of Fusobacteria andCetobacterium were lower than its control. The microbial diversity and abundance ofintestinal flora in xylan group was higher than its control. The ratio of Fusobacteria andCetobacterium to intestinal flora was higher than its control, and the abundance of Proteobacteria and Caulobacter was lower than its control.The above results suggested that pectin and xylan had little effect on the growthperformance of Eriocheir sinensis. However, they have a great influence on the growthand feed conversion of Pelteobagrus fulvidraco. The reason may lie in the differentgastrointestinal tract morphology. Pectin and xylan may inhibit the reabsorption of bilesalts and lipid metabolism, and lead to a decline in the growth performance ofPelteobagrus fulvidraco.