cMOS enhanced the mucosal immune function of skin and gill of goldfish (Carassius auratus Linnaeus) to improve the resistance to Ichthyophthirius multifiliis infection

of supporting mucosal immune barrier integrity and prevention of some pathogenic infections in aquatic species, are key areas of active study, often focusing on feed additives. The objectives of this study were to explore the effects of feeding cMOS (concentrated mannan oligosaccharide) on the gill and skin mucosal barriers of goldfish (Carassius auratus Linnaeus) and evaluate health status during Ichthyophthirius multifiliis infection. After feeding the cMOS-containing diet for 60 days, Hematoxylin and eosin (H&E) staining showed greater length of gill lamella and thicker dermal dense layer, while Alcian Blue and Periodic acid-Schiff (AB-PAS) staining showed higher numbers of mucin cells in cMOS fed fish. Chemical analysis showed that fish fed cMOS had greater enzyme activity of lysozyme (LZM) and alkaline phosphatase (AKP) in gill and skin tissues, while qRT-PCR revealed higher expression of Muc-2 and IL-1β, as well as lower expression of IL-10. After Ichthyophthirius multifiliis challenge, goldfish fed the cMOS diet had lower mortality and infection rates, as well as fewer visible white spots on the body surfaces. Histologically, the gill and skin of these fish presented less tissue damage and fewer parasites, and had a greater number of mucus cells. In addition, the expression of Muc-2 and IL-10 were notably higher while the expression of IL-1β was significantly lower in cMOS fed goldfish than control fed fish. In this study, cMOS fed goldfish had stronger immune barrier function of skin and gill mucous, and better survival following Ichthyophthirius multifiliis infection.