Effect of enzymatic complex in the diet of pirarucu, Arapaima gigas juveniles

ABSTRACT The pirarucu, Arapaima gigas is a native, carnivorous fish species from the Amazon basin. As carnivorous fish have low amylase activity, exogenous enzymes can improve the digestibility of carbohydrates in aquaculture feeds. We evaluated the digestibility of increasing levels of an enzymatic complex in diets of pirarucu juveniles (65.2 ± 0.4 g). The experimental design was randomized with four treatments [diets containing 0.25, 0.50, 0.75, and 1 g kg-1 on-top inclusion of an enzyme complex (Allzyme® SSF®, USA), and a control, with three replications at a density of 5 fish per unit, and a 30-day duration. We quantified apparent digestibility of dry matter, crude protein, and crude energy through nutrient and chromium oxide content in diets and feces. Enzymatic activity, hepatic glycogen and total protein were determined in liver and anterior intestine samples. The diet with 1 g kg-1 of enzyme-complex resulted in an increase in apparent digestibility of crude protein, gross energy, and dry matter, hepatic glycogen, total proteins in liver and in intestine, showing the efficiency of the enzyme complex in pirarucu feeding. A higher accumulation of dry matter, crude energy, and ethereal extract in the carcass indicated weight increase in the fish treated with enzymatic complex. A decrease in the endogenous enzymatic activity (protease, lipase and amylase) suggested an improved efficacy of the digestive process. Our results indicate that the inclusion of 1 g kg-1 enzyme complex in the diet of juvenile pirarucu can be recommended to achieve greater digestibility of nutrients and improvement in productive performance.

摘要
巨骨舌鱼（Arapaima gigas）是原产于亚马逊流域的肉食性淡水鱼类。由于肉食性鱼类的淀粉酶（amylase）活性较低，外源性酶（exogenous enzymes）可提升水产养殖饲料中碳水化合物的消化率。本研究针对不同添加梯度的复合酶制剂在巨骨舌鱼幼鱼（初始体重65.2±0.4 g）饲料中的消化效果开展评估。实验采用完全随机设计，设置4个梯度添加组与1个空白对照组：4个实验组饲料分别以0.25、0.50、0.75及1 g·kg⁻¹的剂量表面添加复合酶（Allzyme® SSF®，美国），每组设置3个重复，每单元养殖5尾幼鱼，实验周期为30天。本研究通过测定饲料与粪便中的营养成分及氧化铬（chromium oxide）含量，量化了干物质、粗蛋白与粗能量的表观消化率（apparent digestibility）；同时采集肝脏与前肠样本，测定了其中的酶活性、肝糖原（hepatic glycogen）及总蛋白含量。
结果显示，添加1 g·kg⁻¹复合酶的实验组，其粗蛋白、总能及干物质的表观消化率，以及肝脏、前肠中的肝糖原与总蛋白含量均显著提升，证实了该复合酶制剂在巨骨舌鱼养殖饲料中的应用效果。该实验组鱼体的干物质、总能及乙醚浸出物（ethereal extract）积累量更高，表明投喂复合酶制剂的幼鱼体重增长更佳。内源性酶活性（蛋白酶（protease）、脂肪酶（lipase）与淀粉酶）的降低，提示消化过程的效率得到提升。本研究结果表明，在巨骨舌鱼幼鱼饲料中添加1 g·kg⁻¹复合酶制剂，可有效提升营养物质消化率并改善生产性能，因此推荐该添加方案。