The dietary protein levels and source of starch are factors in the economical production of feeds, which may change the physical quality of extruded pellets and the growth performance of fish. Eight feeds contained two protein levels and four levels of wheat flour substitutions by corn, as a 2 × 4 factorial experimental design, were produced by a twin-screw extruder machine and fed to 800 rainbow trout. The results showed corn grain reduced expansion ratio, water stability at 120 and 260 min, starch gelatinization (SG), and apparent degradability, while bulk density (BD) and oil leakage of feed pellets increased. The high protein diets displayed the most BD, lower oil leakage, SG, and elastic modulus. The high protein feeds improved the final body weight, weight gain, specific growth rate, and feed conversion ratio (FCR) of fish. The corn grain reduced the FCR and promoted the trout's protein efficiency ratio. Lipid proportions of fish livers corresponded to hepatosomatic index and serum concentrations of aspartate aminotransferase and alanine aminotransferase. In general, corn, as the starch source in the high and low-protein extruded feeds, can be replaced at levels of 33%–66% of wheat flour without adverse effects on the physical characteristics of feed pellets and the growth performance of rainbow trout.

中文翻译：

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日粮玉米和蛋白质水平对膨化饲料颗粒物理特性和虹鳟鱼生长性能的影响

日粮蛋白质水平和淀粉来源是饲料经济生产的因素，可能会改变膨化颗粒的物理品质和鱼类的生长性能。作为 2 × 4 析因实验设计，8 种饲料含有两种蛋白质水平和四种水平的玉米面粉替代品，由双螺杆挤出机生产并喂给 800 条虹鳟鱼。结果表明，玉米籽粒的膨化率、120和260 min水稳定性、淀粉糊化度（SG）和表观降解性降低，而颗粒饲料的堆积密度（BD）和漏油量增加。高蛋白日粮表现出最高的 BD、较低的漏油率、SG 和弹性模量。高蛋白饲料提高了鱼的最终体重、增重、特定生长率和饲料转化率（FCR）。玉米粒降低了FCR，提高了鳟鱼的蛋白质效率。鱼肝的脂质比例与肝体指数以及天冬氨酸转氨酶和丙氨酸转氨酶的血清浓度相对应。一般情况下，玉米作为高蛋白和低蛋白膨化饲料中的淀粉源，可替代小麦粉的33%~66%，不会对颗粒饲料的物理特性和虹鳟鱼的生长性能产生不利影响。 。