Histopathological observations in Neogobius bathybius (Actinopterygii: Gobiidae) infected by Dichelyne minutus (Nematoda: Cucullanidae) in the Caspian Sea, Iran

Dichelyne minutus (Rudolphi, 1819) is a typical and widespread parasite of Gobiidae. In this research, histopathological changes in the intestinal wall of Neogobius bathybius (Kessler) (Actinopterygii: Gobiidae) due to infection caused by D. minutus were studied. The most heavily parasitized regions were excised for microscopic studies. Cross sections revealed different aspects of tissue defensive reactions due to the free movement of nematodes among the gut contents. Mucosal erosion, increased number of goblet cells, hyperplastic changes in the epithelial cells, and remarkable hyperplasia that formed nodule-like structures with hyperemia were observed in the submucosa. Focal necrosis and a thickened muscle layer in the musculature were also noted. These changes may disrupt normal mucosal integrity, cause local blockage of the alimentary canal, and disrupt the overall absorption efficiency of the intestine, and thus the fish’s growth. Therefore, these alterations are significant enough to decrease the level of fitness of the fish by restricting its food intake. Finally, these changes may result in a weaker immune system and fatality.