Nile tilapia farmers must deal with production challenges, such as increased aggressiveness and high stress levels, which potentially diminishes fish welfare. Tryptophan supplementation is a strategy to cope with such problems. However, data is scarce on how tryptophan affects the aggressiveness of this species and other aspects need to be understood on how it influences stress in fish. In this study, we investigate how a 1× (0.32%), 4× (1.28%) and 8× (2.56%) supplemented tryptophan diet affects aggressiveness and stress in Nile tilapia. Aggressiveness in fish was assessed after short-term exposure (7 days) to a tryptophan supplemented diet while stress in fish was assessed after long-term exposure (60 days). The 4x and 8x diets reduced aggressiveness in fish, while the 8x diet reduced aggressiveness more effectively than the 4x diet. Also, long-term exposure to the 8x diet reduced stress in fish, before and after they were exposed to an acute stress. In conclusion, this study showed that a tryptophan supplemented diet can diminish aggressiveness and stress in Nile tilapia, thus demonstrating a potential to improve fish welfare.

中文翻译：

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色氨酸补充剂对尼罗罗非鱼应激和攻击行为的影响

尼罗罗非鱼养殖者必须应对生产挑战，例如攻击性增加和压力水平高，这可能会降低鱼类福利。色氨酸补充剂是应对此类问题的一种策略。然而，关于色氨酸如何影响该物种的攻击性的数据很少，需要了解它如何影响鱼类压力的其他方面。在本研究中，我们调查了 1 × (0.32%)、4 × (1.28%) 和 8 × (2.56%) 补充色氨酸饮食如何影响尼罗罗非鱼的攻击性和压力。在短期暴露（7 天）补充色氨酸的饮食后评估鱼的攻击性，而在长期暴露（60 天）后评估鱼的压力。4x 和 8x 饮食降低了鱼的攻击性，而 8x 饮食比 4x 饮食更有效地降低了攻击性。所以，长期暴露于 8 倍饮食可减少鱼在暴露于急性压力之前和之后的压力。总之，这项研究表明，补充色氨酸的饮食可以减少尼罗罗非鱼的攻击性和压力，从而显示出改善鱼类福利的潜力。