B-glucans: a natural solution to improving the immune status and survival of fish

According the Food and Agriculture Organization - FAO report (2018), of the 171 million tonnes of total fish production in 2016, approximately 88 percent (over 151 million tonnes) was used for direct human consumption, a share that has increased significantly in recent decades. Therefore, to meet the growing demand for fish, fish nutrition and health will play an increasingly important role in the global food Industry.

Intensive fish and shrimp farms are naturally susceptible to bacterial, fungal, and parasitic infections, particularly at times of stress. For a long time, the most common method for dealing with the occurrence of bacterial infections in aquaculture was the administration of antibiotics. However, aquaculture faces serious problems due to various adverse effects of these drugs, such as accumulation in the animals’ tissues and environmental microbiota. Therefore, providing additives that strengthen the immune system might be one of the keys to higher productivity.

ImmunoWall® from ICC Brazil is derived from purified yeast cell walls of Saccharomyces cerevisiae, originating from the sugarcane fermentation process for ethanol production. It is the best natural source of mannan oligosaccharides (MOS) and β-glucans (BG), which are crucial to maintain intestinal health and to improve the immune status, thus ensuring the highest animal performance.

The aggressive conditions during the sugar cane fermentation process to obtain ethanol leads the yeast to protect itself and, therefore, to strengthen its cell wall. Given that β-glucans are like the yeast cell wall "skeleton", it is important to consider the ratio between β-glucans and MOS in order to measure it effectiveness. The higher the β-glucans concentration, the lower the cell wall degradation in the gastrointestinal tract. ImmunoWall® contains around 35% of β-glucans and 20% of MOS, i.e. it has a BG: MOS ratio close to 2: 1, whereas the primary yeast cell walls have a 1: 1 BG: MOS ratio (Figure 1).

Figure 1. The difference in β-glucans between ImmunoWall® and the yeast cell wall from primary fermentation.

B-glucans: a natural solution to improving the immune status and survival of fish - Image 1

Microscopy structural difference between ImmunoWall and Yeast Cell wall from primary fermentation. Light microscopy images performed at Electron Microscopy Facility, Cellular & Molecular Medicine, University of California San Diego – 2016.

MOS is known for its ability to agglutinate pathogens. It prevents pathogen colonization in the gut by offering a binding site to harmful bacteria that possess type 1 fimbriae present in the intestinal tract and is excreted together with the faecal material.

β-glucans are known as immune system modulators or stimulants, since when they come into contact with phagocytes, which recognize the β-1,3 and 1,6 bindings, the phagocytes are stimulated and produce cytokines, which will start a chain reaction inducing an immunomodulation and improving the response capacity of the innate immune system.

This type of response is especially important in animals in the initial growth phase, reproductive phases, stress periods, and during environmental challenges; β-glucans act as prophylactic agents increasing an animal’s resistance and minimizing further damage (such as a drop in performance or high mortality rates). Intensive animal production is a highly challenging environment. Thus, the strengthening of the immunological system can be one of the keys steps toward higher productivity.

In a recently study conducted at the Faculty of Veterinary Medicine, Cairo University, Egypt, by Abu-Elala, et al., (2018), 270 Oreochromis niloticus (50.7±0.8 g of body weight were divided into 3 experimental groups: control, 0.1% ImmunoWall®, and 0.2% ImmunoWall®, with 90 fish in each treatment (3 replicates/tanks). The performance of fish was measured every 2 weeks over 2 months, and at the end of the trial, 5 fish/replicate were euthanised in order to evaluate the relative expression of immune genes using quantitative PCR, phagocytic activity (%) and index, and lysozyme activity (µg/mL) (Table 1). After 2 months, the fish were challenged with the gram-positive bacteria Lactococcus gravaeie and gram-negative Aeromonas hydrophila, and the mortality rates were observed over 1 week (Figure 2).

Table 1. Relative of immune gene expression determined by quantitative PCR, phagocytic activity (%) and index, and lysozyme activity of Nile tilapia challenged with Lactococcus garvaeie and Aeromonas hydrophila.

B-glucans: a natural solution to improving the immune status and survival of fish - Image 2

^abMeans with different letters in the same line differ significantly by according to a Tukey test (P<0.05).

Figure 2. Survivability of Nile tilapia challenged with Lactococcus garvaeie and Aeromonas hydrophila.

B-glucans: a natural solution to improving the immune status and survival of fish - Image 3

^abMeans with different letters differ significantly according to a Tukey test (P<0.05).

These results show that ImmunoWall® was able to improve the immune gene expression response and innate immunity (P<0.05), and therefore reduce the mortality rate (P<0.05), when the fish were challenged with Lactococcus gravaeie and Aeromonas hydrophila, compared to the control group.

The improvement in the immune system reflects directly on performance enhancement. Other studies have demontrated the benefits of ImmunoWall® supplementation in aquaculture on the performance of different species and all have shown an improvement in body weight gain and the feed conversion ratio (Figures 3 and 4).

Figure 3. Body weight gain percentage by fish fed with diets containing ImmunoWall®.

Body Weight Gain Percentage

B-glucans: a natural solution to improving the immune status and survival of fish - Image 4

Tilapia (Oreochromis niloticus): treatments Control and IMW 1g/kg, ABU-ELALA, N. M., YOUNIS N. A., ABUBAKR, H.O., RAGAA, N. M., BORGES, L. L., BONATO, M. A. Efficacy of dietary Yeast Cell wall supplementation on the nutrition and immune response of Nile tilapia. Egyptian Journal of Aquatic Research, 2018. Rainbow Trout (Oncorhynchus mykiss): Treatments Control and IMW 1g/kg, Department of fisheries, Faculty of animal sciences and fisheries, Sari Agricultural Science and Natural Resource University (SANRU), Sari, Iran; 2014. Common Carp (Cyprinus carpioLinnaeus): Treatments Control and IMW1.5g/kg, GH. EBRAHIMI et al., Effects of a prebiotic, Immunogen®, on feed utilization, body composition, immunity and resistance to Aeromonas hydrophila infection in the common carp Cyprinus carpio (Linnaeus) fingerlings, Journal of Animal Physiology and Animal Nutrition, 2011. Kutum (Rutilus frisii kutum): Treatments Control and IMW 0.5g/kg, GH. EBRAHIMI et al. Effects of Prebiotic Supplementation on Survival, Growth Performance and Feed Utilization of Kutum, Rutilus frisii kutum (Kamenskii 1901), Fingerlings, Research Journal of Animal Sciences vol 4 (6) pag. 125-129, 2010.

Figure 4. Feed conversion ratio of fish feed with diets containing ImmunoWall®

Feed conversion ratio

B-glucans: a natural solution to improving the immune status and survival of fish - Image 5

Tilapia (Oreochromis niloticus): treatments Control and IMW 1g/kg,ABU-ELALA, N. M., YOUNIS N. A., ABUBAKR, H.O., RAGAA, N. M., BORGES, L. L., BONATO, M. A. Efficacy of dietary Yeast Cell wall supplementation on the nutrition and immune response of Nile tilapia. Egyptian Journal of Aquatic Research, 2018. Rainbow Trout (Oncorhynchus mykiss): Treatments Control and IMW 1g/kg, Department of fisheries, Faculty of animal sciences and fisheries, Sari Agricultural Science and Natural Resource University (SANRU), Sari, Iran; 2014. Common Carp (Cyprinus carpioLinnaeus): Treatments Control and IMW1.5g/kg, GH. EBRAHIMI et al., Effects of a prebiotic, Immunogen^®, on feed utilization, body composition, immunity and resistance to Aeromonas hydrophila infection in the common carp Cyprinus carpio (Linnaeus) fingerlings, Journal of Animal Physiology and Animal Nutrition, 2011. Kutum (Rutilus frisii kutum): Treatments Control and IMW 0.5g/kg, GH. EBRAHIMI et al. Effects of Prebiotic Supplementation on Survival, Growth Performance and Feed Utilization of Kutum, Rutilus frisii kutum (Kamenskii 1901), Fingerlings, Research Journal of Animal Sciences vol 4 (6) pag. 125-129, 2010. Rutilus kutum Larvae: Treatments Control and IMW 1g/kg, Caspian Journal of Environmental Sciences, Vol. 13 No.1 pag.99-107, 2015.

Intensive animal production is a highly challenging environment. Thus, strengthening the immune system can be one of the key steps to higher productivity. The action of β-glucan occurs on the innate immune system, in other words, where the first immune response to pathogen contamination happens, thus avoiding a higher expenditure of energy during a prolonged inflammation process and mobilizing the adaptive immune system faster, thus avoiding losses in production and high mortality rates.

ImmunoWall® can be supplied early to the animals; it modulates the immune system so that it will be alert to many infections or contaminations.