Salmon farming may face stress due to the intensive culture conditions with
negative impacts on overall performance. In this aspect, functional feed
improves not only the basic nutritional requirements but also the health status
and fish growth. However, to date no studies have been carried out to evaluate
the effect of functional diets in salmon subjected to crowding stress. Thus, the
aim of this study was to evaluate the effect of yeast extract (Xanthophyllomyces
dendrorhous; diet A) and the combination of plant extracts (common Saint John's
wort, lemon balm, and rosemary; diet B) on the antioxidant and immune status of
Atlantic salmon grown under normal cultured conditions and then subjected to
crowding stress. Fish were fed with functional diets during 30 days (12 kg/m3)
and then subjected to crowding stress (20 kg/m3) for 10 days. The lipid
peroxidation in gut showed that both diets induced a marked decrease on
oxidative damage when fish were subjected to crowding stress. The protein
carbonylation in muscle displayed at day 30 a marked decrease in both functional
diets that was more marked on the stress condition. The expression of immune
markers (IFNγ, CD4, IL-10, TGF-β, IgMmb, IgMsec, T-Bet, and GATA-3) indicated
the upregulation of those associated to humoral-like response (CD4, IL-10,
GATA-3) when fish were subjected to crowding stress. These results were
confirmed with the expression of secreted IgM. Altogether, these functional
diets improved the antioxidant status and increased the expression of genes
related to Th2-like response suggesting a protective role on fish subjected to
crowding stress.
