Quantification and localization of mitochondrial-rich cells in the gills of an anadromous fish, Hilsa shad (Tenualosa ilisha)

Tenualosa ilisha has a high economic and valuable marketing in the southern regions of Iran. A recent study was conducted on changes in mitochondrial-rich cells (MRCs) and some blood factors when fish migrated from sea to river. As a model, this research can provide basic information on the osmoregulation functions of this fish and other similar migratory species, and can be useful to other researchers and research centers. Forty mature T. ilisha specimens were collected from the Musa Creek and Arvand Rud. In order to examine the distribution, size, and number of MRCs in the gills, histological sections were observed and analyzed by hematoxylins and eosin staining, immunofluorescent staining, and the scanning electron microscope method. For a better understanding of osmoregulation, plasma ion concentrations of each fish were examined. The antibody staining results showed that in the gills, MRCs were found in lamellae, interlamellar, and basolateral in both the sea and river samples but no MRCs were observed in the filament epithelia. The size and numbers of MRCs in the seawater fishes were considerably larger than those from river water. Concentrations of Na+, Cl-, K+, Ca2+, Mg2+, and glucose in T. ilisha plasma specimens from seawater were significantly higher than the river specimens. According to the study, changes in the gill tissue of T. ilisha during migration can be concluded that this fish easily live in both environments with changes in gill structure and some blood biochemical parameters.