Challenge effect on Mucosal health for Salmon: Trials demonstrate Yeast additive success

By Eric Leclerq, Aquaculture R&D Manager at Lallemand Animal Nutrition

Farmed fish often face germs and stress from their environment. Changes in water quality and management practices can affect their health, welfare, and survival. These may lead to lingering poor performances, secondary infections and diseases outbreak.

Farmers widely use preventive health strategies, such as the use of yeast cell wall (YCW) products, to enhance fish health and performance. Two separate trials tested the same YCW-based products. These trials aimed to show their potential benefits against two different pathogens that affect salmon mucosal tissues.

Amoeba gill disease prevention with YCW

The marine parasite Neoparamoeba perurans causes amoeba gill disease. This parasite damages gills and leads to significant financial losses in the Atlantic salmon industry. It affects many major producing areas. Current treatments include freshwater or hydrogen peroxide bathing both of which can be operationally challenging and biologically challenging.

A 10-week trial took place in Scotland. The goal was to test a new yeast-based ingredient. This ingredient aimed to reduce AGD in Atlantic salmon.

Researchers conducted the trial under controlled conditions. The salmon had an initial weight of 200 to 250 grams. The water temperature was 13 ± 1 °C, and the salinity was 33 ppt.

A post-smolt diet was used to mimic commercial recipes. Researchers tested it in two ways: as is (Control) or with the YCW product (YANG+; Lallemand). The team conducted the tests in quadruplicate.

Fishes were fed to appetite over the trial’s duration. They were reared for five weeks under ideal conditions then exposed to a first standard AGD-challenge followed, two weeks later, by a freshwater bath and a second standard AGD-challenge. The study looked at how diet affects production performance. It also examined the development of gross gill pathology (AGD-scoring) over time.

Improved growth performance

Over the trial’s duration, the functional diet significantly improved specific growth rates (SGR; +20%) as well as feed conversion ratio (FCR; +32%) (Figure 1A and B).

Improved gill score

We scored the gills for AGD lesions to check how the disease is spreading and how severe it is. In this study, we adapted AGD gill-scoring from Gjerde and his team (Gjerde et al. 2019). We scored each gill side to get a fuller picture.

Over the trial’s duration the gill score progressively increased from light to moderate and advanced lesions. At the end of the trial; the proportion of advanced and heavy lesions was significantly reduced in the supplemented group (2-fold and 6-fold respectively) and, inversely, the proportion of fish showing only light lesions was significantly higher (Figure 1C).

Figure 1: A) Specific growth rate (SGR), B) Feed conversion ratio (FCR) and C) Proportion of gill score lesion’s category at the end of the trial *: p<0.05 and **: p<0.01

Tenacibaculum maritimum challenge

Tenacibaculum maritimum is a gram-negative filamentous bacteria ubiquitous in aquatic environment and causing high mortalities in various marine aquaculture species. Tenacibaculosis causes skin ulcers, tissue death, mouth sores, and rotting of the tail and fins. It can also lead to necrosis of the gills and eyes.

Currently, control of tenacibaculosis relies largely on antibiotics with varying degree of efficacy in particular due to the multiplicity of strains. Preventive strategies could help to prevent expansion.

A 15 weeks trial was performed in Canada to test a potential contribution of in-feed supplementation with the YCW product (YANG+; Lallemand) in Atlantic salmon (initial body weight 40 g, 12 ± 1 °C). Researchers produced a baseline commercial diet for Atlantic salmon, supplementing it with YANG+ or leaving it as a control.

Diets were tested in quadruplicate and fed to visual appetite over the trial’s duration. Researchers raised fish in perfect conditions for 5 weeks.

Then, they exposed the fish to a standard T. maritimum challenge by immersion. The trial lasted for 9 weeks after the challenge. During this time, we checked survival and looked for visible lesions on the outer mucosal surfaces regularly.

Improved of survival rate with the functional ingredient

Survival rate was significantly improved in the fish fed the YCW supplemented diet reaching 71.2% survival compared to 58.5% in the Control (Figure 2A).

Reduction of skin lesions severity

The development of skin lesions was the most representative of the disease development in the study. At the end of the trial, researchers found that the ingredient led to a 30% drop in moderate and severe skin lesions (Figure 2B).

Figure 2: A) Survival probability and B) skin score lesions at the end of the second trial (15 weeks).

Conclusion

These trials show the benefits of a new yeast-based ingredient. It helps reduce the severity and deaths from different mucosal diseases in seawater Atlantic salmon. This was connected to stronger skin and gill barriers under ideal conditions (not shown). Interestingly, researchers also noted better growth and feed performance.

These promising results show that this ingredient could help prevent mucosal diseases in the Atlantic salmon industry.