In trout aquaculture, tight control of water quality is crucial, especially for young life-history stages. This study examined whether chronic exposure to moderate hypoxia during the fry stage affects the rainbow trout’s behavior during later development. One month after yolk-sac resorption, young trout were exposed for 25 days to hypoxia, obtained by decreasing water flow and bubbling nitrogen gas into the tank (Hypoxia group, H: mean O₂: 4.85 mg/L; min: 3.83, max: 6.87 mg/L). A control group was maintained in optimal conditions (C: mean O₂: 10.41 mg/L; min: 10.12, max: 10.69 mg/L). At 4 days post-hypoxia, basal (resting) whole body cortisol levels were significantly higher in the H group (166.84 ± 20.67 ng/g) as compared to the C group (103.71 ± 8.78 ng/g), but no post-stress differences were evident (values ∼ 175 ng/g). Long-term effects of hypoxia on various behavioural traits were analysed between 3 and 4 months after the return to normoxia and compared to the C group. The exposure of fry to chronic hypoxia did not impact the fish’s behavioural repertoire (activity, stereotypic behaviour, aggression) in their home tanks after re-acclimation to normoxia. Moreover, basal and post-stress plasma cortisol levels, fear-related behaviours (novel-tank test), and risk-taking behaviours (emergence test) did not differ between the C and H groups. However, this early challenge resulted in an enhanced post-hypoxic growth rate in these fish. Our results show that early exposure to moderate hypoxia does not induce any behavioural changes in rainbow trout after several months of return to normoxia.

在鳟鱼养殖中，严格控制水质至关重要，特别是对于年轻的生命史阶段。这项研究检查了鱼苗期长期暴露于中度低氧是否会影响虹鳟在以后的发育过程中的行为。卵黄囊吸收后一个月，鳟鱼暴露于缺氧状态下持续25天，这是通过减少水流量并向罐中鼓入氮气来实现的（缺氧组，H：平均O ₂：4.85 mg / L；最小值：3.83，最大值：6.87 mg / L）。对照组维持在最佳条件下（C：平均O ₂：10.41 mg / L; 最小：10.12，最大：10.69 mg / L）。缺氧后4天，H组的基础（静息）全身皮质醇水平（166.84±20.67 ng / g）显着高于C组（103.71±8.78 ng / g），但无压力差异明显（值为175 ng / g）。在恢复正常氧后的3到4个月内，分析了低氧对各种行为特征的长期影响，并与C组进行了比较。将鱼苗暴露于慢性低氧状态并不会使其恢复正常状态后，不会影响鱼在其家用水箱中的行为表述（活动，刻板行为，侵略性）。此外，C组和H组的基础血浆和应激后血浆皮质醇水平，恐惧相关行为（新罐测试）和冒险行为（出苗测试）没有差异。然而，这一早期挑战导致这些鱼的缺氧后生长速率提高。我们的结果表明，早期暴露于中度低氧不会使虹鳟恢复正常数月后的任何行为改变。