Histomicroscopy and normal anatomy of the adult killifish Aphanius hormuzensis (Teleostei; Aphaniidae) from the Persian Gulf coastal environment.

The histomicroscopy and normal anatomy of the major body organ systems were investigated in the adult killifish, Aphanius hormuzensis using histological examination, X-ray imaging, double staining, light microscopy and scanning electron microscopy (SEM). Based on the histomicroscopic observations, the kidney, liver and swim bladder in the studied species were comparable to other fish models. The anterior portion of the kidney is bulbous, while the posterior portion is narrow and elongated; the liver has a single lobe and the swim bladder is a single-chambered organ with no connection to the digestive tract (physoclistous). X-ray imaging and double staining examination showed 12 abdominal and 15 caudal vertebrae and a single hypural plate in the caudal skeleton. According to light microscopy, the scales were rounded to pentagonal in shape with three types of radii (primary, secondary and tertiary), and the urohyal bone was elongated. SEM microscopy showed a single row of tricuspid teeth on the upper and lower jaw, respectively, each tooth has two lateral cusps that are shorter than the middle one. The number of teeth was 17-18 in the upper jaw and 19-20 in the lower jaw. The saccular otoliths were rounded-trapezoid in shape with a moderately incised and V-shaped excisura. The members of killifishes are an important group for biologists because of their evolutionary properties, regeneration capacity and usefulness as biological control and also for the ecotoxicological assessment of environmental pollution. The outcomes of this study may provide a useful basis for future research on the genus Aphanius.