Abstract
In the present study, the modulation of the transcriptional immune response (microarray analysis) in the head kidney (HK) of the anadromous fish Atlantic salmon (Salmo salar) fed a diet supplemented with an olive fruit extract (AQUOLIVE®) was evaluated. At the end of the trial (133 days), in order to investigate the immunomodulatory properties of the phytogenic tested against a bacterial infection, an in vivo challenge with Aeromonas salmonicida was performed. A total number of 1,027 differentially expressed genes (DEGs) (805 up- and 222 downregulated) were found when comparing the transcriptomic profiling of the HK from fish fed the control and AQUOLIVE® diets. The HK transcripteractome revealed an expression profile that mainly favored biological processes related to immunity. Particularly, the signaling of i-kappa B kinase/NF-kappa and the activation of leukocytes, such as granulocytes and neutrophils degranulation, were suggested to be the primary actors of the innate immune response promoted by the tested functional feed additive in the HK. Moreover, the bacterial challenge with A. salmonicida that lasted 12 days showed that the cumulative survival was higher in fish fed the AQUOLIVE® diet (96.9 ± 6.4%) than the control group (60.7 ± 13.5%). These results indicate that the dietary supplementation of AQUOLIVE® at the level of 0.15% enhanced the systemic immune response and reduced the A. salmonicida cumulative mortality in Atlantic salmon smolts.
Highlights
The worldwide production of farmed Atlantic salmon (Salmo salar) has progressively increased from 294 t in its inception in 1970 up to 2,615,962.4 t in 2019, with Norway and Chile being the main producers with 1,364,042 t (52.1%) and 701,731 t (26.9%), respectively [1]
We have evaluated a new phytogenic feed additive rich in triterpenic compounds and polyphenols derived from olive fruit (AQUOLIVE®) on the systemic immune response and disease resistance in Atlantic salmon smolts
Analysis of the head kidney (HK) transcriptomic profiling response to a diet supplemented with 0.15% AQUOLIVE® revealed a gene expression profile that favors biological processes related to immunity
Summary
The worldwide production of farmed Atlantic salmon (Salmo salar) has progressively increased from 294 t in its inception in 1970 up to 2,615,962.4 t in 2019, with Norway and Chile being the main producers with 1,364,042 t (52.1%) and 701,731 t (26.9%), respectively [1]. Infectious diseases represent a major problem in worldwide salmon farming, despite the successful development and application of vaccines against a wide range of pathogens and the implementation of management practices for fighting against parasites [2] In this sense, intensified production systems and climate change will favor the occurrence of disease outbreaks due to the farming of more stressed and immuno-compromised animals in farms, and the evolution and spread of more virulent pathogens. Feed additives may be divided into different categories considering the purpose of their use (nutritional, sensorial, and functional additives), which affects their chemical nature and mode of action [10, 11] In this sense, functional feed additives with immunomodulatory properties and capacity of relieving stress and promoting disease resistance in farmed animals are of interest as sustainable health management strategies. Phytogenics are reputed for their growth-promoting effects, as well as their antimicrobial, antioxidant, anti-inflammatory, immunostimulant, and anti-stress properties [10], representing a promising effective and sustainable prophylactic tool to be implemented in health management in front of bacterial and parasitic infections [13, 14]
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