Abstract
BackgroundThe use of phytochemicals is a promising solution in biological control against salmon louse (Lepeophtheirus salmonis). Glucosinolates belong to a diverse group of compounds used as protection against herbivores by plants in the family Brassicaceae, while in vertebrates, ingested glucosinolates exert health-promoting effects due to their antioxidant and detoxifying properties as well as effects on cell proliferation and growth. The aim of this study was to investigate if Atlantic salmon fed two different doses of glucosinolate-enriched feeds would be protected against lice infection. The effects of feeding high dose of glucosinolates before the infection, and of high and low doses five weeks into the infection were studied.MethodsSkin was screened by 15 k oligonucleotide microarray and qPCR.ResultsA 25 % reduction (P < 0.05) in lice counts was obtained in the low dose group and a 17 % reduction in the high dose group compared to fish fed control feed. Microarray analysis revealed induction of over 50 interferon (IFN)-related genes prior to lice infection. Genes upregulated five weeks into the infection in glucosinolate-enriched dietary groups included Type 1 pro-inflammatory factors, antimicrobial and acute phase proteins, extracellular matrix remodeling proteases and iron homeostasis regulators. In contrast, genes involved in muscle contraction, lipid and glucose metabolism were found more highly expressed in the skin of infected control fish.ConclusionsAtlantic salmon fed glucosinolates had a significantly lower number of sea lice at the end of the experimental challenge. Feeding glucosinolates coincided with increased expression of IFN-related genes, and higher expression profiles of Type 1 immune genes late into the infection. In addition, regulation of genes involved in the metabolism of iron, lipid and sugar suggested an interplay between metabolism of nutrients and mechanisms of resistance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1537-y) contains supplementary material, which is available to authorized users.
Highlights
The use of phytochemicals is a promising solution in biological control against salmon louse (Lepeophtheirus salmonis)
The condition factor was lower in control than in fish exposed to GLs: infected C (I-C) group (1.43 ± 0.13), I-low dose feed (LD) (1.54 ± 0.16) and I-high dose feed (HD) (1.52 ± 0.13) (I-LD vs I-C: t-test: t(38) = 2.255, P = 0.030; infected HD (I-HD) vs I-C: t-test: t(38) = 1.65, P = 0.10)
One of the key findings in this study was the massive upregulation of a large group of genes involved in or associated with innate antiviral responses [41] in not-infected high dose (NI-HD) (Fig. 2a-c)
Summary
The use of phytochemicals is a promising solution in biological control against salmon louse (Lepeophtheirus salmonis). The aim of this study was to investigate if Atlantic salmon fed two different doses of glucosinolateenriched feeds would be protected against lice infection. Sea lice infections constitute a major and global problem for salmonid aquaculture. Infection control relies primarily on chemical treatments whose repertoire is limited because of resistance to existing anti-parasitic compounds [1]. In order to apply the optimal treatment, resistance monitoring in lice populations, implemented through a nationwide surveillance program in Norway, could be helpful [1,2,3,4]. Despite differences in the dosage of used chemotherapeutants and increase in the general production of Atlantic salmon, the rise in the number of treated salmon is likely the result of resistance development in sea lice [3, 6]. Finding alternative strategies for managing lice infections is becoming increasingly more important
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