The histology of the esophagus of Oncorhynchus mykiss was studied. The structure of the esophagus exhibited differences as well as similarities when compared with previous studies. In this study, the histochemical and ultrastructural structure of the tunica muscularis externa in the esophagus of this fish is investigated. The muscle fibers are described as red and intermediate fibers according to the pH stability of their mATPase activities. The red fibers showed intense staining, while intermediate fibers showed moderate staining with succinic dehydrogenase (SDH) and toluidine blue. In addition, small diameter fibres were seen. These indicated to be the continuation of development during the structure and function of the esophagus in the juvenile phase. Ultrastructural organization of sarcomeres, Z lines, mitochondria, triads and myofibrils of red and intermediate fibers were different from each other. The myofibrils of intermediate fibres showed clear differences. As a result, it is thought that the histochemical and ultrastructural characteristics of the tunica muscularis externa optimize the performance of the esophagus according to specific functional requirements.

The histology of the esophagus of Oncorhynchus mykiss was studied. The structure of the esophagus exhibited differences as well as similarities when compared with previous studies. In this study, the histochemical and ultrastructural structure of the tunica muscularis externa in the esophagus of this fish is investigated. The muscle fibers are described as red and intermediate fibers according to the pH stability of their mATPase activities. The red fibers showed intense staining, while intermediate fibers showed moderate staining with succinic dehydrogenase (SDH) and toluidine blue. In addition, small diameter fibres were seen. These indicated to be the continuation of development during the structure and function of the esophagus in the juvenile phase. Ultrastructural organization of sarcomeres, Z lines, mitochondria, triads and myofibrils of red and intermediate fibers were different from each other. The myofibrils of intermediate fibres showed clear differences. As a result, it is thought that the histochemical and ultrastructural characteristics of the tunica muscularis externa optimize the performance of the esophagus according to specific functional requirements.