Morphological studies on the gills of the European hake (Merluccius merluccius, Linnaeus, 1758)

The current work gives concern to study the morphology of the Merluccius merluccius gills by using gross morphology, scanning electron microscopy (SEM), and light microscopy. The findings of the present study revealed that the gill system consisted of four pairs of gill arches which carry the gill filaments on the convex border and gill rakers on the concave border of them. SEM results revealed that the rakers and the spines distribution on the first gill arch differed from that of the other three gill arches on the lateral and medial surfaces. On the surface the gill filaments, there were longitudinal ridges that carried pores of chloride cells and mucous cells. The histological examination revealed that, the gill arch composed of hyaline cartilage that presented in the form of cups. Each cup consisted of central cartilagenous core and peripheral cartilagenous matrix. The gill filaments composed of cartilaginous bar of peripheral cartilaginous matrix and central cartilaginous core extended from the gill arches and covered by an epithelial layers with a few mucous cells permeate it, and chloride cells were straggly in the interlamellar epithelium. Each gill filament carried several leaves like secondary lamellae on both sides of it. The epithelium, which lined the secondary lamellae, composed of epithelial pavement cells, some mucous cells, and pillar cells.