Aspergillus niger mycelium at Citribel's facility in Tienen, Belgium. A study concluded that it was as good or better than a yeast-based beta-glucan feed ingredient for enhancing resistance to ulcerative infections.

A sweet result: how a sugar by-product can help salmon battle bacteria

Gareth Moore editor
Published Modified

A feed ingredient made from a by-product of sugar refining has been shown to significantly boost survival rates of Atlantic salmon following infection challenges with pathogens Tenacibaculum maritimum and Moritella viscosa.

Contract research organisation Onda (formerly the Centre for Aquaculture Technologies Canada) carried out the study using the feed ingredient MycoFence, which contains β-glucans derived from Aspergillus niger, a mycelium (root-like structure of a fungus) supplied by Belgian company Citribel.

Researchers aimed to evaluate the in-feed efficacy of three inclusion levels (0.1, 0.2, and 0.3%) of novel Aspergillus niger β-glucan (MycoFence) against ulcerative T. maritimum and M. viscosa infection compared to commercial Saccharomyces cerevisiae yeast β-glucan at its recommended inclusion rate of 0.1%, and a non-enriched control diet. Salmon groups were fed one of the five diets for 5-6 weeks before being the infection challenge.

From sidestream to immunity booster

Sugar molasses, the largest side stream from sugar refineries, is the ideal nourishment for the Aspergillus niger fermented by citric acid and mycelium producer Citribel. During the fermentation process, the fungus produces long fibres (mycelium) which convert the sugar in the molasses to liquid citric acid that is further processed to produce a variety of substances.

Citribel’s process produces a huge amount of mycelium – enough each day to cover six football fields – much of which is sold under the name Citrocell as a protein-rich ingredient for livestock feed.

MycoFence is sold as a powder from which the proteins have been extracted, leaving a pure isolate high in β-glucan content.

Lower mortality

In the Tenacibaculum challenge, mortality rates for fish fed 0.2% and 0.3% MycoFence (mortality of 48.4% and 47% respectively) were similar to the rate for fish fed 0.1% yeast β-glucan (48.2%) and much lower than the control group (66.4%) and the group fed 0.1% MycoFence (64.3%).

In the Moritella challenge, fish fed 0.3% MycoFence performed best, with a mortality rate of 59.5%, followed by those fed yeast β-glucan (65.2%). Fish fed 0.1% MycoFence had 66.1% mortality, better than those fed 0.2% MycoFence (69.2%) and the control group (72.4%).

Expression of cr3, a β-glucan receptive immune marker, was increased in fish fed 0.3% MycoFence compared to 0.2 % inclusion or 0.1 % yeast β-glucan inclusion.

Growth performance, lesion severity, and haematology were unaffected by diet.

Excellent candidates

The researchers concluded that the β-glucan MycoFence provides protection to Atlantic salmon against ulcerative skin diseases Tenacibaculosis and winter ulcer comparable to or greater than yeast-derived β-glucan.

“Taken together, the results indicate that MycoFence provides immune protection through a cr3-mediated mechanism related to the shuttling of phagocytosed bacteria to the head kidney, allowing fish from the 0.3 % dietary inclusion group to most efficiently take up bacteria,” wrote the researchers in the journal Aquaculture (see preview here).

“The suggested mechanism of MycoFence opens a novel avenue of investigation, as the results are suggestive the potential of MycoFence to enhance vaccine-mediated protection against bacterial infection. In conclusion, MycoFence and other A. niger derivatives are excellent functional feed candidates for salmonid aquaculture.”

moritella viscosa citribel atlantic salmon news mycofence β-glucans tenacibaculum maritimum