Abstract
In the context of intensive aquaculture, meagre (Argyrosomus regius) is one of the most important new aquaculture species in Southern Europe and several studies are focused on the optimization of its culture. Nevertheless, stressors such as handling during transport or culture maintenance may affect the immune system, thereby impairing some immune responses or provoking cellular damage. One strategy that has been used to avert this type of negative stress response is the supplementation of amino acids to improve resistance to stress. In this experiment, meagre (105.0 ± 2.6 g, mean ± standard deviation) juveniles were fed two diets for a period of 7 days, the first a commercial diet supplemented with 1% tryptophan (Trp) and second, the same commercial diet without tryptophan supplementation (control group). The effects of two types of handling stressors (air exposure and confinement/netting) on fish fed both diets was evaluated in terms of gene expression of the selected gut immunity markers, such as (1) innate immune response processes: c3 complement (c3), lysozyme (lys), and cyclooxygenase (cox2); (2) humoral immune response processes: interferon type 1 (ifn1), mx protein (mxp), interleukin 1b (il-1b), tumor necrosis factor 1a (tnf1a), and interleukin 10 (il-10); (3) antimicrobial peptides: defensin (def), hepcidin (hep), piscidin (pis), and a marker for mitochondrial respiration: glyceraldehyde 3-phosphate dehydrogenase (gapdh). Samples of the anterior intestine were collected at 1 and 6 h post-stress (hps). Results showed that in fish fed 1% Trp, the air exposure resulted in an upregulation of gene expression at 6 hps for c3, lys, cox2, ifn1, mxp, il-10 and gapdh, and il-1b and pis. The confinement/netting test for fish fed 1% Trp resulted in an upregulation of c3 and mxp and a downregulation of cox2, ifn1, il-1b, tnf1a, il-10, def, hep, and gapdh at both post-stress times (1 and 6 hps). According to the present study, dietary supplementation with 1% Trp may be considered as a proper nutritional strategy for improving tolerance and/or alleviating acute response to handling stressors.
Highlights
Interest in animal welfare has increased in the last decade because of ethical or legal concerns, as well as its effect on growth performance and product quality (Ashley, 2007; Noble et al, 2012; Toni et al, 2019)
Gene expression of several key genes of the innate and humoral immune system was assessed in A. regius juveniles fed C and T diets before and after air exposure (A) and confinement/netting stressors (N)
Since it has already been demonstrated that the stressors tested in the current study resulted in an increase in plasma cortisol levels in the same group of animals (Fernández-Alacid et al, 2019), we investigate the cascade of gene expression that follows the primary stress response in the intestine to understand whether the addition of L-tryptophan in the diet could alleviate the impact of handling stressors on the local gut immunity
Summary
Interest in animal welfare has increased in the last decade because of ethical or legal concerns, as well as its effect on growth performance and product quality (Ashley, 2007; Noble et al, 2012; Toni et al, 2019). Recent advances in the field of aquafeed formulation have led to the development of new feed strategies, using so-called “functional feeds,” to enhance the sustainability of fish production, concerning the growth, survival, and health of the animal by reducing the stress imposed during different handling processes and/or modulating immune functions (Olmos-Soto et al, 2015) In this sense, different nutritional studies have demonstrated that dietary supplementation with essential amino acids, which are precursors to other significant biomolecules, i.e., biogenic amines, heme, or purine and pyrimidine groups (Nelson and Cox, 2013; Andersen et al, 2016), can improve several physiological functions that regulate key metabolic pathways in the organism improving survival, development, growth, health, welfare, and reproduction in different vertebrates, including fish species (Li et al, 2009). Meagre (Argyrosomus regius) fed with a diet supplemented with Trp modulated its serological immune parameters after stress caused by air exposure (González-Silvera et al, 2018)
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