| A 130-days feeding experiment was conducted to study the effect of different levels of Yeast Culture(0,500,1000,1500,2000,2500 mg/kg) and the disconnected group (1000,2000 mg/kg) in dietary on the growth,feed efficiency,physiological function,intestinal villus and disease resistane of Megalobrama amblycephala, and compared the effect of series group with the disconnected group. The fish(an average of 9 g), were randomly assigned to eight dietary treatments with three replicates and fifteen fish with each pen.The 0 mg/kg Yeast Culture is the control group,take result as timed.The 100-days results showed that the SGR of the series group 2000 mg/kg is the highest, more 11.64% than the control group, and the series group are higher than the parallelism disconnected group(P<0.05);The FCR of the series group 2000 mg/kg is the lowest, lower 14.13% than the control group, and the series group are lower than the parallelism disconnected group;The PER of the series group 2000 mg/kg is the highest, higher 13.44% than the control group, and the series group are higher than the parallelism disconnected group;the fullness index of the treatment group have no significant difference with the the control group(P>0.05),however, the Internal organ index is smaller than the control group significantly(P<0.05).The protein in muscle,hepatopancrea,whole body is higher than the the control group's(P<0.05),and the series group are higher than the parallelism disconnected group;the series group 2000 mg/kg is the highest (the protein in muscle), higher 6.3% than the control group.The results of physiological function shows that: the function of immunity,transm- inase,blood making become stronger as long as the Yeast Culture used. the series group are better than the parallelism disconnected group and the series group 2000 mg/kg is the best,the SOD activity of Serum,Phlegm and Hepatopancreas enhanced 65.6%,13%and5.8%compared with the the control group.The LSZ activity of Serum enhanced 16.7% compared with the the control group. The GPT,GOT activity of Hepatopancreas enhanced 2.1% and 8% compared with the the control group.the content of Hb enhanced 10.56% compared with the control group.By anatomizing of the intestine gut and scanning electron microscope of the intestinal mucosa can be observed:â‘ the midgut is longer than the foregut and hindgut,it is the mostly main place of digesting food;â‘¡the drape of mucosa become more and more tight as the yeast culture used,and the 1500 mg/kg and 2000 mg/kg group are mostly distinct;â‘¢the villus of intestine gut have the regular distributing of hexagon,and the density of villus in foregut and midgut are similar, the density of experiment groups are bigger more or lose compared with the the control group,and the series group 1500 mg/kg is the largest, enhanced 67.33% compared with the the control group, the disconnected group have no difference with the parallelism series group;â‘£The height of villus in midgut is bigger than the foregut's, and the height of villus has marked change as the yeast culture used, height of the series group 2000 mg/kg is the highest, enhanced 14.07% compared with the control group, The height of villus of the other group is lower than the control group, The height of villus of the disconnected group are lower than the parallelism series group.A challenging test was conducted by injecting the back muscle of Megalobrama amblycephala with the Aeromonas hydrophila. The results shows that the suitable dosage of yeast culture (1500 mg/kg,2000 mg/kg,2500 mg/kg) can enhance the disease resistane of Megalobrama amblycephala to the Aeromonas hydrophila; The effect of the series group 2000 mg/kg was the best, and the rate of death were only 50%,60% and 80% of the control group for 72 hours,96 hours and 120 hours; The effect of series use is better than the disconnected.These results indicated that the requirements of Megalobrama amblycephala for yeast culture is about 2000 mg/kg diet,and used in series is better than in disconnected.
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