Some morphological structures and histological features of the gills of Binni (Mesopotamichthys sharpeyi)

Abstract

This study aimed to describe some morphological and histological aspects of the binni fish's gills. Fifteen adult male binni were pulled alive from the Al-Forat River at about (24 - 28) months, immediately after death. The gills of binni were situated on each side of the head beneath a gill cover; the operculum and the gills were made of finger-like long filaments joined to the cartilaginous gill bar. From each filament, numerous fragile lamellae that resemble leaves protrude. These lamellae comprised tiny capillaries covered in plain squamous epithelial cells. The epithelium acts as a barrier between the fish's blood and the surrounding water. The first, second, third, and fourth pairs of gill arches make up the gills supported by the bone skeleton. Each arch carries a row of gill filaments on its convex side and two rows of gill rakers on its concave side. On the rostral concave border, the filaments in the two extremes of the gill were short, but the length of all the filaments was the same. The first-gill arch's lateral rakers were longer than the medial rakers, while the fourth gill arch's medial rakers were longer than the lateral rakers. The rakers, bony comb-like projections, filled the rostral region of the gill arches at the rostral concave interior side. There was interdigitation between the gill rakers of the neighboring gill arches. Each gill arch included the lateral gill rakers pointing dorsolaterally and medial gill rakers pointing dorsomedially. Filaments originate from the gill arches and are maintained by the cartilage on the caudal convex border of the primary lamellae, from which the secondary lamellae emerge. The simple squamous epithelium lined the secondary lamellae. Keywords: Binni, Gill, Morphology, Histology