Fasting affects the intestine and bacterial flora in mudskippers (Boleophthalmus pectinirostris) in semiaquatic and underwater conditions

Abstract Fasting alters the structure of the intestine and its bacterial diversity, affecting the metabolism of three nutrients (sugar, fat, and protein). However, very little information is available on the effects of fasting on fish intestinal structure, bacterial flora, nutrient metabolism, and inflammation. In this study, fasting modified the intestinal bacterial floral compositions and diversity in mudskippers (Boleophthalmus pectinirostris), and altered the dominant flora in both semiaquatic (SA) and underwater (UW) conditions. The length of the intestinal villi and the thickness of the intestinal mucosa/submucosa decreased significantly during fasting. The intestinal mucosa/submucosa thickness of the SA group was obviously thinner than that in the UW group. The constitutive expression of glucose, long-chain fatty acid, and amino acid transporter mRNA was detected by real-time quantitative PCR. Expression was dramatically increased in the intestine after fasting. Interestingly, the expression of most of the transporters mRNA associated with energy metabolism was higher in the SA group than that in the UW group. Fasting also induced a pro-inflammatory response in the early and middle stages and an anti-inflammatory response in the middle and late stages. The fish intestine is more likely to present pro-inflammatory symptoms in SA and anti-inflammatory symptoms in UW. The results demonstrated that fasting plays a crucial role in the modulation of structure and function in the intestine and bacterial flora. The function of the fish intestine recovers more quickly after fasting in SA than that in UW.