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（Pirarucu，学名Arapaima gigas）是亚马逊地区极具社会与经济价值的鱼类物种，当地常采用土塘开展养殖。巴西的集约化网箱养殖正逐步兴起，可作为巨骨舌鱼养殖的替代模式，有助于降低养殖成本、提升生产效率。本研究评估了天然饵料生物在半集约化（土塘）与集约化（网箱）两种养殖系统中的作用，以及其对育成初期巨骨舌鱼生长性能与经济指标的影响。实验设置4个300㎡的土塘与4个4.0m³的网箱，分别放养120尾（密度0.4尾/㎡）与160尾（密度40尾/m³）幼鱼，初始体质量为28.03±6.34g，初始标准体长为11.75±0.80cm。实验周期为105天，养殖过程中投喂商品配合饲料。每两周对鱼类生长情况与浮游生物摄食情况进行一次监测。结果显示，土塘养殖组的存活率、标准体长、增重率与终末体质量均显著高于网箱养殖组；土塘组的饲料转化率（0.96±0.06）低于网箱组（1.20±0.11）。尽管两种养殖系统均投喂人工配合饲料，但均观测到鱼类摄食天然饵料生物的现象。胃内浮游动物与昆虫的相对丰度与土塘组鱼类的增重呈正相关，与网箱组则呈负相关。土塘养殖组的经济效率更高，平均生产成本更低。本研究结果表明，巨骨舌鱼（Arapaima gigas）育成初期的成本效益在土塘养殖系统中更优。