A review on the activity of Na+/K+-ATPase in branchial ionocytes and its role in salinity adaptation among diadromous species

Jumah Yashier Upling Jumah Yashier Upling

doi:10.30574/wjarr.2020.6.2.0158

Abstract

Freshwater and saltwater environments have opposite osmotic gradients. In freshwater, organisms tend to uptake ions from the surrounding, while in saltwater, they need to excrete the excess ions. Branchial ionocytes play a significant role in euryhaline teleost species that migrate to different salinity gradients as part of their life cycle. Ionocytes are highly dependent on the activity of Na+/K+-ATPase (NKA) in salinity adaptation. Thus, this review article determines the factors affecting NKA activity in ionocytes and its role in salinity adaptation among diadromous species. Several findings suggest that NKA activity is affected by various factors such as hormones, nutrition, and gene expression. Ionocytes enriched with NKA have many functions in diadromous depending on their types, location, size, and number in branchial necessary for these organisms to carry out their biological function in ionic-regulatory processes.

Highlights

Several species of fish utilizing different osmotic gradient habitats for forage, reproduction, development, settlement, refuge, and others
The branchial ionocytes is one of the major features of fish gill anatomy that is useful in salinity adaptation
Species that migrate from freshwater to marine water as part of their life cycle have a well-established ionocyte type in their gills

Summary

Introduction

Several species of fish utilizing different osmotic gradient habitats for forage, reproduction, development, settlement, refuge, and others. The size of the NKA cells of freshwater and seawater individuals showed larger than that of brackishwater fish [10] This different pattern of NKA activity with regards to salinity adaptation was reported in Oryzia species. Prolactin is known as a fundamental endocrine factor for hyper-osmoregulation in teleost fishes, acting on ionocytes in the gills to maintain ion concentrations of body fluid within narrow physiological ranges in freshwater conditions This was shown to maintain the density of freshwater-type ionocytes in isolated gill filaments; this effect of prolactin is not achieved by the activation of cell proliferation, but by the maintenance of existing ionocytes. The gilthead sea bream S. aurata is a euryhaline fish where prolactin and growth hormone plays a role in the adaptation to different environmental salinities In this species, growth hormone increased branchial NKA activity and decreased sodium levels in line with its predicted hypo-osmoregulatory action [32]. Feed deprivation tends to reduce physiological, metabolic, ion-osmoregulatory, and molecular compensatory mechanisms limiting the fish’s ability to adapt to a hypo-osmotic environment [37]

Ontogeny of branchial ionocytes in fish

Findings

10. Conclusion