The Fate of Dietary Tryptophan in Fish: Unveiling Its Sources, Transport, Metabolism, and Multifaceted Impacts.

The rising need for sustainable protein sources has made aquaculture vital for securing food supply. A balanced protein-rich diet is essential to support the optimal growth, health, and productivity of farmed aquatic species. Tryptophan, an essential amino acid, plays a crucial role in protein synthesis and serves as a precursor for neurotransmitters such as serotonin (5-hydroxytryptamine) and melatonin, which regulate reproduction, appetite, stress, and aggression in fish. The shift toward sustainable feed solutions emphasizes the need for tryptophan supplementation to address the deficiencies in alternative protein sources. Tryptophan supplementation promotes growth by enhancing protein synthesis, muscle development, and nutrient absorption while mitigating stress and inflammation through serotonin and melatonin synthesis. Its antioxidant properties help regulate oxidative stress, protect against environmental damage, and improve fish resilience. Tryptophan also modulates immune functions and reproductive processes, highlighting its multifaceted significance in aquaculture. Tryptophan interacts synergistically with other nutrients to enhance growth and immune responses. However, imbalanced tryptophan levels can impair growth, immune function, and productivity, thus requiring precise dietary formulations. The optimal tryptophan requirement varies among species and target functions. This review aims to highlight the pivotal role of tryptophan in fish health, growth, stress regulation, immune responses, oxidative damage, reproduction, cannibalism and its interaction with other nutrients, demonstrating its potential to further enhance immune function and support metabolic regulation.