Effect of diets containing probiotic yeast Cystobasidium benthicum and fruit Cyrtocarpa edulis on growth and immune parameters of Nile tilapia (Oreochromisniloticus).

This study investigates Cystobasidium benthicum (Cb) probiotic yeast and Cyrtocarpa edulis (Ce) fruit dietary effects, single (0.5 %) or combined (Cb:Ce, 0.25:0.25 %), on growth performance, humoral immunity in serum and skin mucus, and intestinal morphology of Nile tilapia (Oreochromis niloticus) after 14 and 28 days. The Cb group presented the highest (P < 0.05) specific growth rate, weight gain, and absolute growth rate with respect to the control group. Immunological assays indicated that Cb, Ce and Cb:Ce groups increased serum nitric oxide concentration compared to the control group (P < 0.05). Cb and Cb:Ce groups showed the highest serum myeloperoxidase enzyme activity at day 14 and 28, respectively (P < 0.05); whereas, Cb:Ce group had the highest (P < 0.05) myeloperoxidase activity in skin mucus. The superoxide dismutase enzyme activity was unaffected. On day 28, Cb, Ce, and Cb:Ce groups showed higher and lower (P < 0.05) catalase enzyme activity in serum and skin mucus, respectively, compared with the control group. Only the Cb group had higher (P < 0.05) total protein concentration in serum (day 14) and skin mucus (day 14 and 28) with respect to the control group. The lysozyme activity in serum (day 28) and skin mucus (day 14) was higher (P < 0.05) in the Cb group compared to the control group. Only the skin mucus of Ce group showed bactericidal activity against Aeromonas dhakensis (P < 0.05). Histological studies indicated that Cb and Cb:Ce groups increased microvilli height, and Cb, Ce and Cb:Ce augmented goblet cell area at day 14 compared to the control group (P < 0.05). At day 28, microvilli height was higher in all groups and the number of intraepithelial leukocytes increased in Cb and Ce groups with respect to the control group (P < 0.05). The ex vivo assay revealed that A. dhakensis in leukocytes decreased cell viability similar to the control group (P < 0.05). A principal component analysis (PCA) confirmed the results. In conclusion, C. benthicum in the diet was the best supplement to improve the growth and immunity of Nile tilapia.

ß-Glucan bioactivities from Cystobasidium benthicum in Totoaba macdonaldi thymus cells.

The overuse of antibiotics in aquaculture has led to serious concerns on microbial resistance and chemical residues. Novel sources of immunostimulants could help to solve this problem by stimulating the immune system to fight against pathogens. Therefore, this study aims to explore the immunostimulant potential of Cystobacidium benthicum-ß-glucans (Cb-ßG) using thymus cells from Totoaba (Totoaba macdonaldi), a recently farmed fish species in Mexico. The Cb-ßG was characterized and tested for its own antioxidant capacity. Then, a Cb-ßG safety experiment was carried out in thymus cells by evaluating the effects on immune parameters and immune-related genes. Cb-ßG had a molecular weight of 2.32 kDa, comprised of ß-1,3-1,6-glucan (53.4%), and showed strong antioxidant capacity compared to that of the positive antioxidant control. Cb-ßG had no toxic effects of thymus cells and enhanced phagocytic, respiratory burst, myeloperoxidase and superoxide activities. Additionally, immune-related genes implicated in recognition and effector functions of yeast glucans were up-regulated (Toll like receptor 2, C-type lectin family 17 member A, colony-stimulating factor 1 receptor 2, macrophage mannose receptor 1, and Interleukin-1ß). In conclusion, the glucan -characterized physically-chemically from the yeast C. benthicum (Cb-ßG)- was safe, had strong antioxidant capacity to scavenge free radicals, and stimulated immune parameters and immune-related gene expressions on thymus cells from Totoaba macdonaldi.

Yeast ß-Glucans as Fish Immunomodulators: A Review.

Administration of immunostimulants in fish is a preventive method to combat infections. A wide variety of these biological molecules exist, among which one of the yeast wall compounds stands out for its different biological activities. The ß-glucan that forms the structural part of yeast is capable of generating immune activity in fish by cell receptor recognition. The most frequently used ß-glucans for the study of mechanisms of action are those of commercial origin, with doses recommended by the manufacturer. Nevertheless, their immune activity is inefficient in some fish species, and increasing the dose may show adverse effects, including immunosuppression. Conversely, experimental ß-glucans from other yeast species show different activities, such as antibacterial, antioxidant, healing, and stress tolerance properties. Therefore, this review analyses the most recent scientific reports on the use of yeast ß-glucans in freshwater and marine fish.