Pathological studies of the major respiratory organs of Paramisgurnus dabryanus with the inhibition of intestinal aerial respiration

To clarify the physiological effects of intestinal aerial respiration on Paramisgurnus dabryanus, the histopathology of the main respiratory organs of P. dabryanus was investigated by inhibiting the intestinal aerial respiration in this study. The results showed that the inhibition of intestinal aerial respiration could cause the death of P. dabryanus around one week post inhibition. When the fish from the experimental group were moribund, the gills, dorsal skin, anterior intestine, mid intestine, posterior intestine, and rectum were collected and subjected to Hematoxylin-eosin (H.E) staining, Alcian-Blue Periodic Acid-Schiff (AB-PAS) staining and scanning electron microscopy (SEM). The results showed that: ① by H.E staining, the gill terminal of the fish from the experimental group was congested, the blood capillary in the epidermis of dorsal skin were contracted and decreased, and dermis cells were deformed. The plicamucosa of anterior intestine was enlarged; meanwhile the connective tissues were denser in the rectum as well as with the exudation of red blood cells (RBc) in the serosa of posterior intestine. ② by AB-PAS staining, the gills, dorsal skins, posterior intestine, and rectum of the fish from the experimental group revealed an increase in acidophilic vacuoles. Besides, the amount of acid mucoprotein on the lamina propria of the anterior and middle intestines increased in the experimental group. By contrast, the neutrophil mucoprotein in submucosa layer decreased in the experimental group. ③ by SEM, the surface of the gill lamellae was damaged and detached, resulting in wrinkling, together with the increased number of secretory pores on the surface of dorsal skin. More bumps were observed on the inner surface of middle intestine of fish from the experimental group. In addition, the granules on the inner surface of the posterior intestine and the rectum of the fish from the experimental group were increased. Taken together, inhibition of intestinal aerial respiration could cause an increase of the mucous cells and exudation of RBcs in the main respiratory organs, and eventually it could lead to death. In summary, intestinal aerial respiration is the necessary physiological activity of P. dabryanus. The current results will shed a new light on the seeding cultivation and sustainable culture of P. dabryanus.