Does L-tryptophan supplementation prevent the effect of stress on the circadian oscillator of trout gastrointestinal tract?

Aquaculture is a rapidly growing industry that faces significant animal welfare challenges due to the high demand for its products. The intensification of farming can lead to increased overcrowding and competition for resources, which can be a significant source of stress. Considering both challenges, it is crucial to focus on refining management practices and enhancing animal welfare in fish farms. In organisms, the circadian system regulates rhythmic functions, including various physiological and behavioral processes such as the response to stress. A deeper understanding of the circadian system contributes to improving animal welfare. The present study evaluated the effect of stress on the relative expression of clock genes in the gastrointestinal tract of rainbow trout (Oncorhynchus mykiss) fed a regular or L-Tryptophan-enriched diet, to determine if the amino acid mitigates this effect. The results suggest that diets supplemented with L-Trp in non-stressed animals cause an increase in cortisol levels and changes in the rhythmic profiles of the different clock genes analyzed. These changes are similar to those produced in the stressed group but lacking L-Trp. However, in stressed animals fed L-Trp, it was observed that the supplementation partially prevented the effects of stress on most of the parameters assessed. These preliminary results suggest that supplementing diets with the amino acid is only beneficial if the animals are expected to be exposed to stress.