Fig. 3

Genes related to mediate intestinal air-breathing and digestion/absorption in fish. a The number of hemoglobin (hb) gene family and digestion/absorption-related gene families shown in the blue circle and salmon color circle, respectively. The total number of hb gene family and digestion/absorption-related gene families is shown in the gray circle. The circle sizes are equivalent to the gene number that was observed. Both Misgurnus anguillicaudatus and Triplophysa tibetana belong to Cobitidae. Loach M. anguillicaudatus is an air-breathing fish, while T. tibetana is a non-air-breathing fish. b The structures of posterior intestines of Leptobotia elongate (non-air-breathing fish) and the loach, and the expression profiles of five air-breathing-related genes (namely five DEGs) in the posterior intestines of L. elongate and the loach. The blue triangles represent goblet cells (GC for short) and the black triangles represent the red blood cells(RBC for short). The black box represents expression profiles of DEGs in the posterior intestines of loach between the control and air exposure group. c The presence and absence of the five DEGs in five fish species. DEGs, differentially expressed genes. Cldn5, claudin-5; vegfr1, vascular endothelial growth factor receptor1; Mis0158000.1, which is a new gene and annotated as interleukin 1 beta (il1b); ctgf, connective tissue growth factor; hspb1, heat shock protein beta-1