A yeast probiotic for managing white feces syndrome

Jean-Benoît Darodes de Tailly, Alban Caratis, Nadège Richard, Phileo by Lesaffre

In the current landscape of intensive shrimp farming, optimizing costs while maintaining high productivity has become a critical balancing act. With profit margins growing increasingly slim, shrimp farmers are under tremendous pressure to maximize efficiency and minimize losses. One of the most daunting challenges impeding this goal is the White Feces Syndrome (WFS), a pervasive gastrointestinal issue primarily affecting the hepatopancreas, the shrimp’s largest and most crucial organ. WFS is a multifactorial syndrome that generally arises from a disruption of the intestinal balance rather than a single pathogen, complicating its prevention and treatment. Numerous factors are believed to trigger WFS, including bacterial infectionscombined with parasitic infestations, poor water quality, chronic stress, or low-quality diets. This makes WFS a poorly understood and complex condition that poses significant difficulties for farmers.

 

Traditional responses to WFS often involve costly treatments and interventions, further squeezing already tight profit margins. This situation underscores the necessity for cost-effective, preventative solutions that address and alleviate the root causes of WFS.

What makes yeast probiotics promising candidates?

 

Yeast probiotics are well-known for their efficacy in alleviating various gut disorders in both animals and humans. They are frequently included in commercial medicines and supplements aimed at treating conditions like diarrhea and irritable bowel syndrome (IBS).

 

Their application in managing gut disorders in shrimp farming, however, is still emerging, with limited but promising research. The observed benefits of live yeast in shrimp farming are likely due to its combined prebiotic, probiotic and postbiotic actions. Yeast cell walls contain α-mannans and 1.3/1.6 β-glucans which are known to have beneficial effects on shrimp gut health and immunity (Ran et al., 2015). The same β-glucans might also have a beneficial impact on lipid metabolism, a key component of the shrimp’s hepatopancreas, as reviewed by Machuca et al. (2022). The metabolic byproducts of live yeast such as organic acids and vitamins can also influence the microbial community within the hepatopancreas, crucial for the availability of digestive enzymes and efficient nutrient absorption. The same components have also been documented to reduce gut inflammation and oxidative stress, as well as improve gut integrity in aquaculture species (Ran et al., 2015; Rohani et al., 2022).

 

Yeast probiotics, therefore, play an important role in stabilizing the gut environment and preventing pathogenic infections from escalating, which is crucial for managing conditions like WFS and opens new avenues in the search for solutions to mitigate WFS.

Figure 1. Clinical trial timeline
Figure 2. Shrimp from the negative control (NC) and the positive control (PC). Arrow No. 1 points towards a full gut, arrow No. 2 points towards a white gut while arrow No. 3 shows a pale hepatopancreas.

Approach to reproducing WFS under experimental conditions

 

Research on WFS under experimental conditions presents several challenges, notably due to the absence of a universally accepted protocol and the multifactorial and complex pathogenesis of the condition described earlier.

To evaluate the potential of Actisaf SC47, Phileo’s reference yeast probiotic, in mitigating the impact of WFS, Phileo by Lesaffre, with the support of ShrimpVet lab (2023), developed an adaptation of the co-infection model originally proposed by Caro et al. (2021, Fig. 1).

 

This model leverages the unique combination of pathogenic Vibrio bacteria and Enterocytozoon hepatopenaei (EHP), an intracellular microsporidian parasite, to induce WFS. As illustrated in Figure 1, EHP acts as a primary infection, disrupting the normal digestive and absorptive functions of the hepatopancreas as well as its role in immunity. This disruption intends to create an open door for secondary infections and intensifies the impact of opportunistic bacteria like Vibrio spp., contributing to the development of WFS.

 

For the study, twenty experimental units were mobilized and distributed into four groups, each with five replicates. Shrimp were housed in 350L tanks, with 60 shrimp per tank, stocked at an average weight of 1.5 grams. The trial spanned 57 days, aiming to accurately assess within this experimental framework the efficacy of Actisaf SC47 in mitigating WFS when applied either through feed or in granulated form in water. Considering the kinetic progression of WFS, two sampling points were conducted at 16 and 26 days after the initial infectious challenge.

 

At both sampling points, the co-infection model effectively induced WFS in the positive control, as illustrated in Figure 2. Typical symptoms of WFS were observed in the shrimp, marked by the presence of white, stringy fecal strands and a general reduction in feed intake and gut content. These external observations were also coherent with microscopic findings, revealing a disrupted hepatopancreas (HP) architecture, demonstrating the model’s effectiveness in replicating the syndrome under experimental conditions.

Figure 3. Shrimp from the Actisaf Water group (AW) and the Actisaf Feed group (AF).

Figure 4. (A) Percentage of deformed HP tubules and (B) gut health score in shrimp treated with Actisaf® compared to control groups at the end of the trial (mean ± S.E.). For (a), different letters indicate significant differences (p<0.05).

Hepatopancreas health management, crucial for controlling WFS

 

In contrast, Actisaf® supplementation both through water and feed was found to have a substantial protective effect against the incidence of WFS symptoms when compared to the positive control (Fig. 3, 4).

 

Microscopic analyses revealed that live yeast administration helped maintain the structural integrity and nutrient reserves of the HP in infected shrimp. To document these improvements, hepatopancreas health scores were implemented between groups, evaluating measurable factors such as lipid droplet content (i.e., energy storage), tubule deformation, and the proportion of aggregated transformed microvilli (ATM) inside the tubules (Sriurairatana et al., 2014). Additionally, a general hepatopancreas health score was calculated from the 3 metrics mentioned above to provide a summary of the HP health status.

 

Actisaf® supplementation in both water and feed resulted in a significantly lower proportion of deformed tubules compared to the positive control (Fig. 4A). Additionally, both supplemented groups showed numerical improvements in lipid droplets content and lower ATM presence. This resulted in higher health scores for both groups supplemented with Actisaf® compared to the positive control (Fig. 4B).

 

This preservation of HP health status in Actisaf®- treated shrimp suggests they maintained more normal nutrient uptake, energy storage capabilities and immune status compared to the positive control group, despite similar loads of Vibrio and EHP in the hepatopancreas. These findings are significant, indicating that Actisaf® can enhance resistance to WFS even under substantial pathogen presence, offering protective effects against damage.

The healthier the hepatopancreas, the greater the benefits

 

The improvement of the hepatopancreas condition also resulted in substantial performance gains. Both water and feed applications of Actisaf® led to significantly higher survival rates compared to the positive control group, with increases of 43% and 22%, respectively (Fig. 5A). Additionally, survivors in the feed application group exhibited a 12% increase in final body weight compared to the positive control group, matching the weight of unchallenged shrimp (Fig. 5B).

 

Feed conversion ratios (FCR) were notably lower in Actisaf®-supplemented groups compared to the positive control and were on par with the negative control, reflecting the improved hepatopancreas condition and enhanced lipid reserves as previously described. Moreover, the coefficient of variation in shrimp size, reflecting size uniformity, was numerically lower in groups supplemented with Actisaf® compared to the positive control. This suggests that Actisaf® supports more consistent growth despite the presence of EHP, which typically causes size disparities.

Figure 5. (A) Survival rates and (B) final body weight in shrimp tanks supplemented with Actisaf® compared to control groups at the end of the trial (mean ± S.E.). Different letters indicate significant differences (p<0.05).

Conclusion

 

White Feces Syndrome poses a significant global challenge for shrimp farmers, with annual industry costs estimated close to at least a billion dollars – a figure that is likely to grow even more as we continue to shift toward more intensive production practices. The supplementation of Actisaf® has shown remarkable abilities in providing protection to the hepatopancreas of shrimp during WFS outbreaks, resulting in substantial performance improvements in infected shrimp. Lesaffre has filed a patent for the use of Actisaf® against White Feces Syndrome.

 

Just as yeast probiotics are used in human and livestock health to combat gastrointestinal diseases, their strategic application in aquaculture underscores the potential for biological interventions. More research is now needed to fully understand the modes of action and interactions between pathogens and yeast to develop even more effective strategies.

 

References available on request

For additional information about fermentation solutions for shrimp farming, visit Program Aquasaf Shrimp.

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