| This thesis is to use two sizes of large yellow croaker as the research object. Using four kinds of soybean meal by different processing to replace fish meal, evaluating the feasibility of the replacement of fish meal by different kinds of soybean meal, and measuring the appropriate replacement level based on the growth performance,body composition, thyroid hormone levels, antioxidant enzymes, antibacterial ability, digestive enzymes, the digestibility in vitro and histomorphology.In test one,nine isonitrogenous and isoenergetic diets were formulated with fish meal,four kinds of soybean meal(dehulled soybean meal, enzyme-treated soybean meal, fermented soybean mealⅡ, fermented soybean mealⅠ), corn protein powder, powder spray dried blood and gluten powder as the main source of protein, fish oil and soybean lecithin oil as the main source of fat. The control group(50%fish meal,without soybean meal)and 8 experimental groups formulated by replacing 20% or 40% fish meal with dehulled, enzyme-treated, fermented soybean mealⅡor fermented soybean mealⅠ with crystalline amino acids, respectively. The 9 groups was respectively named as FM,A1,A2,B1,B2,C1,C2,D1,D2. A total of 1080 large yellow croaker( Pseudosciaena crocea R)with an average body weight of(34.72g±0.28g)were randomly divided into 9 groups with 3 replicates each,and each replicate contained 40 fish. Fish were fed with the diets above for 49 days. In test two, seven isonitrogenous and isoenergetic diets were formulated(the groups of fish meal replaced by fermented soybean mealⅠexcluded). A total of 1260 large yellow croaker( Pseudosciaena crocea R)with an average body weight of(7.48g±0.08g)were randomly divided into 7 groups with 4 replicates each, and each replicate contained 45 fish. Fish were fed with the diets above for 45 days. The 7 groups was respectively named as FM,A1,A2,B1,B2,C1,C2.(1)The effect of replacement of fish meal by different kinds of soybean meal on growth performance,body composition and thyroid hormone levels: In test one, there were no significant differences in the survival rate, special growth rate between control group and experimental groups(P>0.05).The feed intake in A1 was higher than the control(P<0.05). But there were no significant differences on feed conversion ratio among all the groups(P>0.05). With the increase of soybean meal, the protein content in the muscle and whole fish had a downward trend.The protein contents in whole fish of A2,B2,C2 and D2 were significant lower than the control(P<0.05). But the fat content was the opposite trend. The amount of triiodothyronine in serum of B1 was significant lower than the control(P<0.05). But there were no significant differences on the amount of thyroxine among all the groups(P>0.05). In test two,the survival rate of the A1 and B2 was significantly lower than the control(P<0.05),but the weight gain rate and special growth rate were no significant difference between replacement groups and control(P>0.05). The feed conversion ratio,feed intake, hepatosomatic index, viscera index and condition factor were no significant difference between replacement group and control( P > 0.05).The feed intake of the C2 was higher than B2(P<0.05).The result of body and muscle composition were same as that in test one. There were no significant differences on the amount of triiodothyronine in serum between replacement groups and control(P>0.05),but the amount of triiodothyronine of C1 were significant higher than other replacement groups(P<0.05).And there were no significant differences on the amount of thyroxine among all the groups(P>0.05).The results of the two tests showed that, fermented soybean meal II can replace 40% of fish meal,and it will not adversely affect the level of thyroid hormone and growth of large yellow croaker. In test one, dehulled soybean meal and enzyme-treated soybean meal can replace 40% of fish meal,while in test two, the survival rate were lower in the group of 20% fish meal replaced by dehulled soybean meal or 40% fish meal replaced by enzyme-treated soybean meal.(2) The effect of replacement of fish meal by different kinds of soybean meal on antioxidant enzymes, antibacterial ability: In test one,the superoxide dismutase activity and catalase in serum, liver and mucus were significantly different among groups(P<0.05). The malondialdehyde in serum and liver of replacement groups were higher than the control group(P<0.05). Serum showed significantly lower capacity to kill V.harveyi in the group of 40% fish meal replaced by enzyme-treated soybean meal and lower capacity to kill V. alginolyticus in the group of 20% fish meal replaced by dehulled soybean meal(P<0.05). Serum and mucus showed no significant differences on the capacity to kill A. hydrophila among all the groups(P<0.05). Fermented soybean meal did not affect serum and mucus to kill the three kinds of bacteria.Test two: the superoxide dismutase activity in serum were no significant difference between replacement groups and control(P>0.05),but the superoxide dismutase activity in liver in C2 were higher than the control(P<0.05). The lysozyme activity in serum was higher than A2,B1 and B2(P<0.05). The malondialdehyde in serum in B1 were higher than other groups. The malondialdehyde in liver were higher in the group of fish meal replace by dehulled soybean meal and enzyme-treated soybean meal than the group of fish meal replace by fermented soybean mealⅡand control(P<0.05). Serum showed significantly lower capacity to kill V.harveyi and V. alginolyticus in the group of 20% fish meal replaced by dehulled soybean meal. Serum showed significantly lower capacity to kill V.harveyi in the group of 40% fish meal replaced by enzyme-treated soybean meal.From the results of the two tests, serum showed no significant differences on the capacity to kill the three kinds of bacteria in the group of 20% fish meal replaced by dehulled soybean meal or 40% fish meal replaced by fermented soybean mealⅡ.(3) The effect of replacement of fish meal by different kinds of soybean meal on digestive enzymes, the digestibility in vitro and histomorphology:In test one,protease activity, lipase activity and amylase activity in liver and intestinal were not affected by the kinds of soybean meal. With the increase of replacement level, protease activity in the stomach has a downward trend.The protease activity in the stomach of C1 were higher than B2 and C2(P<0.05). The muscle layer of intestine were thinner in A2 and B2 than other groups.The intestinal villus were sparser in A2 and B2. The fold height were lower in A2,B2 and C2 than other groups. In test two, the protease activity in stomach were lower when the fish meal replaced by dehulled soybean meal and enzyme-treated soybean meal.And the lipase activity in stomach were lower when the fish meal replaced by enzyme-treated soybean meal. The protease activity in intestine were increased when 20% fish meal replaced by fermented soybean mealⅡ. The digestibility of fish meal in vitro were no significant difference among all groups(P>0.05).But the digestibility of different kinds of soybean meal were significantly different among groups(P<0.05). The digestibility of different kinds of soybean meal in liver were higher in B1,B2 and C2(P<0.05). The digestibility of different kinds of soybean meal in stomach were lower in B2,and that of different kinds of soybean meal in intestine were lower in A1 than B2 and C2(P<0.05). The hepatocytes were sparser in A2,B2 and C2 than control,and the vacuolization in liver were more serious in A2, B2 and C2.When 20%fish meal was replaced by soybean meal, the hepatocytes were more dense, the vacuolization in liver were less serious. The intestinal villus were sparser and the fold height were lower in B2. The muscle layer of intestine were no significantly different among groups,but higher level of replacement by soybean meal destroyed the intestinal integrity. From the results of the two tests, digestive enzyme activity in the digestive tract were affected by the content of soybean meal. The intestinal villus were sparser and the fold height were lower in the group of 40%fish meal replaced by soybean meal.Based on the growth performance,body composition,thyroid hormone levels, antioxidant enzymes, antibacterial ability, digestive enzymes, the digestibility in vitro and histomorphology, enzyme-treated soybean meal, fermented soybean mealⅡand fermented soybean mealⅠcan replace 20% fish meal,and the group of 20% fish meal replaced by fermented soybean mealⅡwas the best. |
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