ISSUE FOCUS 56 FEED & ADDITIVE MAGAZINE August 2025 BACTERIAL PATHOGEN RESPONSE Building on the AGD findings, a second trial examined whether similar mucosal health benefits could be observed against bacterial pathogens. Tenacibaculum maritimum (T. maritimum) is a gram-negative filamentous bacterium ubiquitous in aquatic environments, which causes high mortality in various marine aquaculture species. Tenacibaculosis is associated with ulcerative skin, tissue necrosis, mouth erosion, tail and fin rots, and necrosis of the gills and eyes. To date, no consistently effective methods are available due to the multiplicity of strains and antibiotics used. Other preventive strategies aiming at maintaining fish healthy could help prevent expansion of such bacteria challenge. A 15-week Canadian trial tested the same yeastbased diet used in the Scottish study. A standard commercial diet for Atlantic salmon with an initial body weight of 40 g, maintained at 12±1 °C, was either supplemented with YCW or not as the control. Diets were tested in quadruplicate and fed to visual satiation over the trial’s duration. Fish were reared in ideal conditions for five weeks during which smoltification occurs. At the end of this period, fish were confronted with a T. maritimum immersion challenge for over five hours. The trial evaluated the diet's effect on survival and reduction of lesions on some external mucosal surfaces such as skin, mouth, and gill. Mortality was recorded daily, and skin, mouth, and gill lesions were scored before and at four time points after the bacterial challenge. Results suggested improved survival probability from 58.5% to 71.2% in fish receiving the experimental diet (p<0.05; Figure 2A). Scoring of mouth, gill, and skin disease allows researchers to evaluate the disease propagation and severity. In this trial, gill and mouth were not the most representative mucosal surface of the bacterial infection, A. Survival Probability 0 10 20 30 40 50 60 Time in days post-challenge Control YCW + 16% - 30% - 30% p = 0.00018 + 22% B. Proportions Diet Control Yeast Cell Wall Light Moderate Lesion category Severe Severe lesion recovered Correspondance Analysis p = 0.008 100 75 50 25 0 100 75 50 25 0 % % Figure 2. Effects of YCW supplementation on Atlantic salmon challenged with Tenacibaculum maritimum. A) Survival probability over 15-week trial period and B) Skin lesion severity distribution at 63 days post-challenge Statistical significance: * p<0.05
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