Morphological investigation of the gills of the dusky grouper Epinephelus marginatus (Lowe 1834) using gross anatomy and scanning electron microscopy.

The current study has designed to investigate the morphological characteristics of the gills of the dusky grouper (Epinephelus marginatus) by gross morphology, scanning electron microscopy, and morphometric analysis. The study was carried out on 10 fresh fish. The fish has four-gill arches on each side. The lengths of the first-, second-, third-, and fourth-gill arches were 5.27, 4.2, 3.2, and 2.8 cm. The gill arches carried a longitudinal band, the bases of the gill filaments, and gill rakers that varied from rectangular to circular shapes. Each gill arch had two main lateral and medial rows and two accessory rows of gill rakers in an alternative manner with each other. The dusky grouper fish had long rakers, whereas the longest one was the lateral rakers of the first arch, which were 467 and 1271.9 μm in width and length. Three types of spines appeared on the gill arches and rakers. The long spine had detected on the apex of the short rakers. Each gill arch carried on its ventral side two rows of gill filaments. The long filaments were at the middle of the gill arch, while the short ones were at the rostral end of the gill arch. The study has demonstrated the taste buds, mucous, chloride cells, and significant features of the epithelial covering of the gill arches and rakers. The morphology of the gills of the dusky grouper indicates the adaptation to their marine environment.