Effect of natural food consumption on the first phase of pirarucu grow-out in ponds and cages

ABSTRACT Pirarucu, Arapaima gigas is a fish species of great social and economic importance in the Amazon region, where they are often farmed in earthen ponds. Intensive cage aquaculture has been growing in Brazil, which could be an alternative means to farm pirarucu, reducing costs and increasing productivity. We evaluated the contribution of natural food organisms in semi-intensive (ponds) and intensive (cages) production systems, and their effect on pirarucu growth and economic performance during the first phase of grow-out. Four ponds (300 m2) and four cages (4.0 m³) were stocked, respectively, with 120 (0.4 fish m-²) and 160 (40 fish m-³) juvenile pirarucu (28.03 ± 6.34 g, 11.75 ± 0.80 cm). The study was conducted for 105 days and fish were fed with commercial feed. Fish growth and plankton intake were evaluated every two weeks. Survival rate, standard length, weight gain and final weight were higher in fish reared in earthen ponds than in cages. Feed conversion of fish kept in ponds was lower (0.96 ± 0.06) than in cages (1.20 ± 0.11). The consumption of natural food organisms was observed, despite artificial feed being fed in both systems. The relative abundance of zooplankton and insects in stomachs was directly proportional to fish weight gain in ponds, and inversely proportional in cages. Higher economic efficiency rate and lower average production cost were calculated for earthen ponds. Our results indicate that the cost-benefit of the first phase grow-out of A. gigas is better in earthen ponds.

摘要：巨骨舌鱼（Arapaima gigas）是亚马逊地区兼具重要社会与经济价值的鱼类物种，当地常将其养殖于土塘中。集约化网箱养殖在巴西日渐兴起，可作为巨骨舌鱼养殖的替代模式，有助于降低成本、提升生产效率。本研究评估了半集约化（土塘）与集约化（网箱）两种养殖系统中天然饵料生物的贡献，以及它们在巨骨舌鱼育成初期对生长与经济表现的影响。本研究设置4个面积300平方米的土塘与4个体积4.0立方米的网箱，分别放养120尾（密度0.4尾/平方米）与160尾（密度40尾/立方米）的巨骨舌鱼幼鱼（初始体重28.03±6.34克，体长11.75±0.80厘米）。试验持续105天，期间投喂配合饲料。每两周对鱼类生长与浮游生物摄食情况进行检测。结果显示，土塘养殖的巨骨舌鱼存活率、标准体长、体重增重与终末体重均高于网箱养殖个体。土塘组的饲料转化率（0.96±0.06）低于网箱组（1.20±0.11）。尽管两种系统均投喂人工饲料，但仍观测到鱼类对天然饵料生物的摄食行为。胃容物中浮游动物与昆虫的相对丰度与土塘组鱼类的体重增重呈正相关，而与网箱组呈负相关。土塘组的经济效率更高，平均生产成本更低。本研究结果表明，巨骨舌鱼育成初期的成本效益在土塘养殖模式中更优。