Mechanical abrasion stimulation: Altered epidermal mucus composition and microbial community in grass carp (Ctenopharyngodon idella)

Abstract

In modern high-density farming, seasonal change, fishing, transportation, and other conditions easily cause mechanical abrasion of fish skin. This leads to alterations in the material balance of the epidermal mucus composition of fish, preventing normal immune function. Subsequently, the risk of disease increases. In this study, grass carp (Ctenopharyngodon idella) was used as an object to investigate immune-related enzyme activities, structural characteristics, and physiological changes of its epidermal mucous cells caused by mechanical abrasion. Furthermore, we explored the changes in body surface mucus composition and microbial community diversity and structure. Our results showed that mechanical abrasion stimulation, significantly changed the activities of immune-related enzymes, such as lysozyme (LZM), alkaline phosphatase (AKP), and acid phosphatase (ACP) were within 24 h (P < 0.05). Their levels gradually recovered after 48 h. In contrast, no significant change was observed in superoxide dismutase (SOD) levels. The number of mucous cells increased, especially those of type I and type II mucous cells in the dorsal skin, which were significantly increased (P < 0.05). Meanwhile, the stimulation changed the metabolites composition of the fish epidermal mucus in the short term, upregulating 12-OPDA, indole, quinic acid and GSH, which are beneficial to antibacterial and anti-inflammatory, and downregulating L-saccharopine, L-2-aminoadipic acid, spermine, GSSG and ribose 5-phosphate, which disrupt protein synthesis, energy production and DNA synthesis. Additionally, these metabolite changes further affect the composition of microorganism communities, rising the abundance of certain disease-associated microorganisms, such as Acidovorax, Rhizobiaceae, Aurantimicrobium, and Leifsonia, which increases the risk of disease in fish. The findings of the present study provide a deeper understanding of the role of mucus as a component of the immune system in fish and provide a scientific basis for effective grass carp culture management and disease control.