Abstract
The transcriptomic response of the head kidney, the main lymphohematopoietic tissue of the body, was evaluated in Atlantic salmon (Salmo salar) smolts fed a functional feed containing a phytogenic rich in verbascoside and triterpenic compounds like ursolic acid. Fish (initial body weight = 55.0 ± 0.1 g) were fed two experimental diets (40% crude protein, 22% crude fat; 21.6 MJ/kg gross energy) that only differed in the phytogenic content (0.1% inclusion). Each diet has six replicates and was tested over a period of 133 days. The tested zootechnical feed additive a medicinal plant leaf extract (MPLE) obtained from sage (Salvia officinalis) and lemon verbena (Lippia citriodora). At the end of the trial, smolts fed the MPLE diet were heavier than their congeners from the control group (271.5 ± 7.9 g vs. 240.2 ± 19.3 g, respectively; P < 0.05). Feed conversion ratio (FCR) values in fish fed the control diet were higher than those in fish fed the MPLE diet (FCRcontrol diet = 1.27 ± 0.08 vs. FCR0.1% MPLE diet = 1.08 ± 0.05; P < 0.05). The immunomodulatory properties of the functional diet were evaluated by means of an in vivo challenge with Aeromonas salmonicida subsp. salmonicida (1 × 107 CFU mL–1). The microarray analysis of head kidney samples from both dietary groups revealed 1,178 differentially expressed genes (802 upregulated and 376 downregulated). Among them, several biological processes related to immunity were identified in fish fed the MPLE diet (i.e., interferon-gamma-mediated signaling pathway, antigen processing and presentation of peptide antigen via MHC class II, autophagy, regulation of i-kappaB kinase/NF-kappaB signaling, and leukocyte activation). Results from the bacterial challenge showed that survival rates were higher in smolts from the MPLE group (90.6 ± 6.4%) in comparison to the control group (60.7 ± 13.5%), confirming the functional benefits of the phytogenic in terms of host’s immunity and disease resistance. Biological processes such as cytoskeleton organization and regulation of cellular protein metabolic process detected in fish fed the MPLE diet supported the metabolic changes related to increased somatic growth promoted. The present findings showed that the inclusion at 0.1% of the tested MPLE obtained from sage and lemon verbena in diets for Atlantic salmon smolts promoted somatic growth, and enhanced their systemic immune response and reduced mortality when fish were challenged with A. salmonicida cumulative, the causative agent of furunculosis in salmonids.
Highlights
Aquaculture is predicted to be the main source of aquatic dietary protein sources by 2050, playing a relevant role in food security and supply, as well as in poverty alleviation (Stentiford et al, 2020)
We found that the inclusion of medicinal plant leaf extract (MPLE) at 0.1% in Atlantic salmon smolts exerted a positive effect on somatic growth, being fish fed the diet containing the MPLE 11.5% heavier than the control group
Phytogenics obtained from sage and lemon verbena included at 0.1% in diets promoted somatic growth and improved feed conversion ratio (FCR) in Atlantic salmon smolts
Summary
Aquaculture is predicted to be the main source of aquatic dietary protein sources by 2050, playing a relevant role in food security and supply, as well as in poverty alleviation (Stentiford et al, 2020). Despite the sector’s efforts focused on competitiveness and sustainable development to build this thriving sector, this rapid and continuous growth of the salmon farming has some side effects In this sense, under intensive farming, fish can be influenced by various environment-related biotic and abiotic factors that can have potentially harmful or stressful effects (Taranger et al, 2015). Under intensive farming, fish can be influenced by various environment-related biotic and abiotic factors that can have potentially harmful or stressful effects (Taranger et al, 2015) All these factors have a negative impact on fish welfare and overall rearing performance, increasing susceptibility to disease; negatively impacting the industry by causing health crises and economic losses (Tort, 2011; Taranger et al, 2015). This makes aquatic animal diseases one of the main factors limiting the growth of aquaculture and its sustainability (Reverter et al, 2020; Naylor et al, 2021)
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