Tenacibaculosis and winter ulcers, skin-associated diseases, have caused substantial economic losses in the global farming of salmon. The absence of effective vaccines and the problems associated with consistent antibiotic use necessitate the development of alternative treatments, such as oral feed additives. β-glucans have previously displayed immunomodulatory activity against skin-based disease in finfish and are, therefore, strong candidates. They are naturally derived from a variety of sources, and most bioactive β-glucans are produced by fungi. Evidence suggests that β-glucan structural diversity has a species-specific component, which may result in different immunomodulatory activity and potency. Despite this, there is a gap in animal health literature regarding diverse β-glucan sources because most research solely references Saccharomyces cerevisiae derived β-glucans. Thus, this study investigated the in-feed efficacy of novel Aspergillus niger β-glucan (Mycofence®) against ulcerative Tenacibaculum maritimum and Moritella viscosa infection compared to commercial S. cerevisiae β-glucan and a non-enriched control.
Atlantic salmon were fed one of five diets for 5-6 weeks and assessed for growth performance before T. maritimum or M. viscosa challenge. Feeding continued throughout challenge, wherein different diet groups were monitored for mortality and sampled for lesion severity and immune response through hematology and gene expression. Growth performance (weight gain and FCR), severity of lesion and hematology were unaffected by the diets. The transcript expression of immune markers in the gut (sclra, cr3, igT and cxcl2) and head kidney (tlr5, cox-2 and myd88) and absolute quantification of T. maritimum and M. viscosa is under evaluation, and will be discussed. Mortality after T. maritimum challenge was comparably reduced by 0.2 and 0.3% Mycofence® and 0.1% yeast β-glucan, however, and was reduced significantly after M. viscosa challenge by 0.3% Mycofence® (see Fig. 1.). A. niger-derived β-glucan therefore provided comparable or improved protection against T. maritimum and M. viscosa infection to commercial yeast β-glucan. This finding highlights the relevance of investigating non-yeast sources of β-glucan as immunomodulators and reinforces the potential of A. niger β-glucan to the salmon industry as a sustainable and environmentally friendly approach to preventing disease outbreaks.