Physiological and metabolic effects of a tryptophan-enriched diet to face up chronic stress in meagre (Argyrosomus regius)

Abstract

It is known that tryptophan (Trp) can attenuate the stress response in fish though its role in chronic stress has been scarcely studied. In this work, the effects of a Trp-enriched diet on stress, metabolism and immune parameters have been analysed from an integrative perspective and using novel methods. Several meagres were submitted to crowding and netting stress during four months. Trp diets did not affect growth or zootechnnical parameters. Plasma stress markers response was not altered significantly in the Trp treatments. Those results were correlated to the mucus parameters and, in addition, several skin immune properties improved in the Trp treatments. Overall, the activity of enzymes related to amino acid and carbohydrate metabolism decreased in the Trp-enriched groups. Trp-supplemented diets increased the liver kynurenine concentration under stress, as well as liver tryptophan in non-stressed fish. The present work shows the first data on the effects of Trp-enriched diets on chronic stress in the meagre. The continuous feeding with 0.25% Trp supplements could improve the meagre welfare, with no effect on productive performance, by keeping or reducing the stress markers; reinforcing the immune system; mitigating the energy metabolism; and enhancing the amino acid reserves.