| A 8-week feeding trial was conducted to study the effects of feed yeast on growth performance, immunity and intestinal microscopic structure of Scophthalmus maximus. Five kinds of isocaloric and isonitrogenous diets ( 0 (B1), 17% (B2), 34% (B3), 51% (B4) and 68% (B5) fish meal were replaced with 0, 15%, 30%, 45% and 60% of feed yeast) were formed. A total of 195 fish (initial weight: 9.02±0.15g) were averagely allocated to 15 glasses tanks with 3 replicates of 13 turbot in each replicate. The fish were fed 3%-4% body weight thrice daily and the amount of feed given was increased as the fish grew. The results showed that weight gain, feeding ratio, special growth ratio, hepatopancreas indexes, viscera indexes and condition factor were all suffered from the trend of first increased and then decreased, the trend of feed conversion ratio was opposite. Weight gain, specific growth rate and survival rate of B2 were 16.82%, 4.95% and 11.99%, respectively, which were higher than that of the control group, and it’s feed conversion rate (12.42%) was lower than that of the control group.This proved that appropriate dietary feed yeast to some extent could promote the growth of turbot. However, a over certain ration of feed yeast addition will significantly reduce the growth of turbot. With the increase of feed yeast, crude protein decreased, while crude ash gradually increased, moisture and crude lipid had no significant differences. Compare with the control group, the crude protein of B2 was significantly higher than 5.84% and crude ash was lower than 22.44%. It proved that appropriate dietary feed yeast to some extent could also promote the nutritional quality of turbot. The effect of feed yeast on immunity was not obvious when the addition of feed yeast was 30% (except SOD activity), it will have a significant reduction in the immune indexes when over 30%. As the addition of feed yeast increased, intestinal folds were gradually decreased, while the numbers of intestinal flora were not changed significantly. The intestinal construction of the turbot was damaged by excessive feed yeast. The structural integrity of anterior intestine and mid-intestine in B5 was destroyed, the part of intestinal villi shed. The intestinal villi of posterior intestine were shorter, the proper layer became wider and the connective tissue of proper layer loosened. The ingredient cost, feed cost and production cost were all lower than the control group when 15% feed yeast was added. The ingredient cost saved 1.19 yuan per kg, feed cost saved 1.62 yuan per kg and production cost saved 4.76 yuan per kg. The overall conclusion was that the optimal feed yeast addition in diets may be set at 15% based on the results of growth performance, physical indicators, body composition, immunity, intestinal microscopic structure and feed cost. |
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