Free nucleotides, β-glucans,andMOS: The perfect combination to increase the survival rate and fish and shrimp production
by Liliana Borges and Melina Bonato, P&D ICC Brazil
The wide expansion of commercial aquaculture, over the last 15 years,has been followed by a global increase in fish farmed in fish ponds. However, producers face health-related issues with the consequent use of medications, like in any intensive farming activity, which causes tissue and environmental microbial floraaccumulation.
Fish, like mammals, have an innate and an adaptive immune system; the innate system provides quick, primary, unspecific and no-memory responses against recontamination. On the other hand, the adaptive system provides specific responses or, in other words, intense responses using pathogen-specific antibodies.
Macrophages, neutrophils, dendritic cells,and natural killers are the most widely known cells in the innate immune system. Toll-type receptors, located on the surface of immune cells, recognise microbial standards and induce an immediate innate immune response.
After such induction and phagocytosis, phagocytes show the adaptive immune system a processed fragment of the pathogen and stimulate a non-pathogenic response. Therefore, phagocytes are called antigen-presenting cells. Pathogen recognition, by the innate immune system, triggers immediate innate defenses and, subsequently, activates an adaptative immune response.
Therefore, the use of compounds or diet additives to increase the survival rate, disease resistance and growth of fish and shrimp have been more frequent and more successful.Sacharomyces cerevisiae yeast is a natural and immunostimulant additive used in farming to promote better intestinal health, thus resulting in greater disease resistance and better production rates.
Yeast is composed of manno-oligosaccharides (MOS) and β-glucans1.3-1.6and isa rich source of RNA and amino acids, especially glutamine and cytoplasm proteins.
To make these nutrients fully available, ICC Brazil, a leader in the production of yeast-based compounds for animal nutrition, has developed Hilyses® - hydrolyzed Saccharomyces cerevisiae yeast obtained from sugarcane fermentation in ethanol production. The yeast is RNA and polypeptide hydrolysed by some added specific enzymes, resulting in free nucleotides and nucleosides, highly-digestible amino acids, and short-chain peptides and polypeptides. Hilyses® also contains yeast cell wall, composed of MOS and high levels of β-glucans 1.3-1.6 (immune system modulators).
Free nucleotides and nucleosides can be readily absorbed by enterocytes in the intestine and are especially important in rapidproliferation of cell tissues, having limited capacity for de novo synthesis.Free nucleotides can be used by the recycling pathway, where the body can synthesise nucleotides using less energy, resulting from recycling bases and nucleotides from the metabolic degradation of nucleic acids derived from dead cells or food. However, when endogenous supply is insufficient, the (food) sources of exogenous nucleotides can become semi-essential nutrients.
Although nucleotides are not strictly defined as immunostimulants, they are bound to this process, as they provide the immune system with substrates and co-factors needed for the activity, considering that they are involved in all cell processes.
The use of nucleotides in fish nutrition has several benefits, including increased food intake, rapid intestinal repair, and improved intestinal flora in the mucosa and mucosal surfaces. These have been used in aquaculture as a source of nitrogen or as a functional food for water animals, and can compensate for insufficient nucleotides in food with high content of vegetable protein.
Every component in Hilyses® provides a synergetic effect, improving intestine integrity and health, promoting higher cell proliferation and strengthening the immune system. This is important for animals during accelerated growth periods (initial phases), reproduction, stress and challenging conditions posed by diseases.
In a study conducted by Abu-Elala, et al. (data not published) in Cairo University School of Veterinary Medicine, in Egypt, 270 Oreochromis niloticus (50.7 ± 0.8 g of body weight) were used and divided intothree experimental groups: Control, 0.2 percent and 0.4 percentHilyses®; and 90 fish were assigned to each treatment group (3 repetitions/tank).
Fortwo months, fish performance was measured every twoweeks and, at the end of the study, five fish/repetition were euthanised to assess clinicopathological parameters, oxidative and antioxidative substances, immune-related gene expression by quantitative PCR, phagocytosis activity and rate (%), and lysozyme activity (µg/mL).
After two months, fish were challenged with Gram-positive Lactococcus garvieaeand Gram-negative Aeromonas hydrophila bacteria, and mortality rates were observed for one week.
Hilyses®diet supplementation at 0.4 percent increased fish body weight after two months in 32.6 g (+33.3%) compared to the control group. Additionally, there was a 67.3 percent weight gain increase and a 28.6 percent reduction in food conversion (P<0.05).
Hilyses® at 0.4 percent improved results for catalase and G-reductase activities (P<0.05).Nucleotides found in Hilyses® provide support to cellular mechanisms that increase antioxidant activity,and β-glucans stimulate the immune system, where some cells produce hydrogen peroxide as a form of defense against bacteria. The joint action of both compounds promotesthe increased activity of antioxidant enzymes (catalase and G-reductase).Hilyses® diet supplementation showed a significant increase in pro-inflammatory cytokines and TNFα immune gene in both supplemented groups and increased IL1-β gene at 0.4 percent (P<0.05).
The innate response was influenced by both treatments, conferring improved phagocytic activity and lysozyme activity, as well as increased phagocytosis rate (P<0.05). β-glucans act in the innate immune system, i.e., where the first immune response to pathogenic contamination is observed, avoiding higher use of energy during an extended inflammatory process and more quickly engaging the adaptative immune system, avoiding production losses and high mortality rates.
The results of L. garvieaechallenge showed that Hilyses® supplementation at 0.2 percent and 0.4 percent reduced mortality in 66.7 percent and 89 percent, respectively. A. hydrophilachallenge showed that Hilyses® at 0.2 percent and 0.4 percent reduced mortality in 60 percent and 100 percent, respectively (P<0.05).
These results confirm the efficacy of β-glucans in the innate immune system, of MOS acting against pathogenic bacteria, and of nucleotides that provide support to immunity cell mechanisms.
Innate immune system modulation can be one of the strategies used to fight contamination, reduce mortality and improve fish and shrimp productivity. When yeast is offered to animals at an early stage, the immune system is modulated and gets ready to detect different infections or contaminations.