This study was conducted to evaluate the effect of using protease in diets of Nile tilapia on growth performance, water quality, blood parameters and intestinal morphology. The cost of these diets and their return on fish performance was calculated. A total of 360 fish were randomly allocated into four groups with triplicates (30 fish per replicate). Four diets were formulated; two controls (without protease supplementation) and two experimental diets (supplemented with protease). The first control diet contained the normal protein requirement (30% CP; control +ve), while the second control had a low protein content (29% CP; control −ve). The third diet was supplemented with protease at a dose of 500 g/ton, and its CP content was reduced to 29.0%, by reducing the fish meal content. The fourth diet contained the same CP level as the first control (30%) and supplemented with 250 g protease per ton feed. The experiment lasted for 14 weeks. The results showed that body weight and length, weight gain, specific growth rate, feed intake and feed conversion efficiency in the control −ve group (low CP) supplemented with protease were similar (p > 0.05) to that of the control +ve with normal CP content. However, these performance parameters were lower (p < 0.05) in fish fed low CP diet without protease supplementation. Providing protease to the control +ve diet improved all measured performance indices. The ammonia and nitrite concentrations of the water were reduced (p < 0.05) in control −ve and protease-supplemented groups. The height and width of intestinal villi were increased (p < 0.05) in fish fed diets containing protease. The inclusion of protease reduced the diet cost and also the feed cost of fish weight gain. In conclusion, supplementation of protease can improve the productive performance of fish, spare dietary protein and produce economical diets. Moreover, it can help in improving the water quality of fish via lowering the ammonia and nitrite contents, or through increasing the degradation of dietary protein.

中文翻译：

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日粮添加蛋白酶对尼罗罗非鱼（Oreochromis niloticus）生长性能、水质、血液参数和肠道形态的影响

本研究旨在评估在尼罗罗非鱼日粮中使用蛋白酶对生长性能、水质、血液参数和肠道形态的影响。计算了这些饮食的成本及其对鱼类性能的回报。共有 360 条鱼被随机分配到四组，一式三份（每个重复 30 条鱼）。制定了四种饮食；两个对照（不补充蛋白酶）和两个实验饮食（补充蛋白酶）。第一个对照饮食含有正常的蛋白质需求（30% CP；对照+ve），而第二个对照具有低蛋白质含量（29% CP；对照-ve）。第三种日粮添加蛋白酶500克/吨，通过降低鱼粉含量，将其CP含量降至29.0%。第四种日粮含有与第一种对照相同的 CP 水平（30%），每吨饲料添加 250 克蛋白酶。实验持续了 14 周。结果表明，补充蛋白酶的对照组（低CP）的体重和身长、体重增加、比生长率、采食量和饲料转化效率相似（p  > 0.05) 与正常 CP 含量的对照 +ve 相比。然而，这些性能参数 在没有补充蛋白酶的低 CP 日粮中较低（ p < 0.05）。向对照+ve饮食提供蛋白酶改善了所有测量的性能指数。 在对照-ve 组和补充蛋白酶组中，水中的氨和亚硝酸盐浓度降低（p < 0.05）。肠绒毛高度和宽度增加（p < 0.05) 在含有蛋白酶的鱼饲料中。加入蛋白酶降低了饲料成本，也降低了鱼增重的饲料成本。总之，补充蛋白酶可以提高鱼的生产性能，节省日粮蛋白质并生产经济的日粮。此外，它可以通过降低氨和亚硝酸盐的含量，或通过增加日粮蛋白质的降解来帮助改善鱼类的水质。