Phenylalanine and Tyrosine as Feed Additives for Reducing Stress and Enhancing Welfare in Gilthead Seabream and Meagre

Abstract

Increased aquaculture production is associated with a growing interest in improving fish welfare. For this reason, the search for strategies to mitigate stress has intensified, one of these strategies being food supplementation with amino acids. The objective of this study was to evaluate the effects of dietary phenylalanine (Phe) and Tyrosine (Tyr) on the stress response and metabolism of juvenile gilthead seabreams (Sparus aurata) and meagres (Argyrosomus regius). Fish batches were fed a control diet and two diets supplemented with 5% Phe or Tyr for seven days. At the end of the experiment fish were stressed by air exposure for 3 min and then sacrificed for the extraction of blood and brain. Classical plasma stress markers were analyzed (glucose, lactate, proteins, cortisol), as well as hormones derived from those amino acids (adrenaline, noradrenaline and dopamine). Despite interspecific differences, fish fed the diets supplemented with Phe or Tyr showed a reduction on several stress markers. However, interspecific differences were detected for many indicators. Concretely, hormonal stress markers were significantly attenuated in meagres fed the enriched diets. Moreover, the stress condition favored a mobilization of amino acids towards the brain, especially in supplemented diets, hence this amino acid excess could be used as an energy substrate to cope with stress.

Keywords: amino acid; feed additive; fish; phenylalanine; stress; tyrosine; welfare.

Figure 1

Plasma glucose, lactate and proteins concentrations (mg dL⁻¹) for each treatment (mean ± SE, n = 10). The white and black bars are the basal and stress values, respectively. Asterisks indicate significant differences between the basal and stress conditions. Different letters indicate significant differences among feeding treatments within every condition.

Figure 2

Plasma cortisol, adrenaline and noradrenaline concentrations (ng mL⁻¹) for each treatment (mean ± SE, n = 10). The white and black bars are the basal and stress values, respectively. Asterisks indicate significant differences between the basal and stress conditions. Different letters indicate significant differences among feeding treatments within every condition.

Figure 3

Plasma T3 and T4 concentrations (ng mL⁻¹) for each treatment (mean ± SE, n = 10). The white and black bars are the basal and stress values, respectively. Asterisks indicate significant differences between the basal and stress conditions. Different letters indicate significant differences among feeding treatments within every condition.

Figure 4

Brain adrenaline, noradrenaline and dopamine concentrations (ng mL⁻¹), for each treatment (mean ± SE, n = 10). The white and black bars are the basal and stress values, respectively. Asterisks indicate significant differences between the basal and stress conditions. Different letters indicate significant differences among feeding treatments within every condition.

Figure 5

Brain Phe and Tyr concentrations (ng mg⁻¹) for each treatment (mean ± SE, n = 10). The white and black bars are the basal and stress values, respectively. Asterisks indicate significant differences between the basal and stress conditions. Different letters indicate significant differences among feeding treatments within every condition.