Ontogeny of the Osmoregulatory Capacity of Teleosts and the Role of Ionocytes

Abstract

Whilst osmoregulation in the adult teleost fish has been extensively studied and significant advances have been made in recent years, much less information exists regarding osmoregulation during the early stages of development of teleosts. Adult fish maintain their blood osmolality in a narrow physiological range, i.e., ≈ 280-360 mOsm kg −1 , through the combined osmoregulatory capabilities of several sites i.e., branchial chambers, skin, digestive system and urinary organs. However, embryonic and post-embryonic stages maintain their blood osmolality in a less narrow range of ≈ 240-540 mOsm kg −1 and osmoregulatory capacity is restricted to the cutaneous ionocytes located on the tegument with a transference in osmoregulatory function occurring during the early life stages to the developing digestive tract, the urinary organs and the developing branchial tissues and the ionocytes which they support. This review will discuss the development of osmoregulatory capacity that occurs throughout early life stages of teleosts and its role in conserving physiological homeostasis, focusing on the form and function of related mechanisms, i.e., the ionoregulatory cell or ionocyte, outlining the different roles and functions of different ionocyte types relative to their environment, i.e., freshwater or seawater, their plasticity and discuss spatio-temporal changes in ionocyte distribution that occur during ontogeny.

Triphenyl phosphate-induced pericardial edema in zebrafish embryos is dependent on the ionic strength of exposure media

“…Zebrafish have emerged as a model teleost species to understand how embryonic and adult fish utilize osmoregulation to maintain homeostasis ( Evans, 2011 ; Fridman, 2020 ; Pung Hwang et al, 2011 ; Pung Hwang and Chou, 2013 ; Kwong et al, 2014 ). As zebrafish gills continue to develop a capacity for O 2 consumption until approximately 14 d post-fertilization (dpf) ( Rombough, 2007 ), aquaporins and epidermal ionocytes play a critical role in maintaining homeostasis within the developing embryos and larvae ( Guh et al, 2015a ).…”

Morpho-Functional Alterations in the Gills of a Seawater Teleost, the Ornate Wrasse (Thalassoma pavo L.), after Short-Term Exposure to Chlorpyrifos

“…No studies are available for comparison with our results, due to the absence of information about Na + /K + -ATPase modulation in seawater fish after CPF exposure. It should be emphasized that the CCs of marine teleost and freshwater teleost are different in their structure and, in part, in their function [ 54 , 55 ]. It is well established that the principal function of the CCs in marine teleost is osmoregulation, but their physiological role in freshwater fish is still under discussion, and both the mechanism and cell sub-types vary amongst species [ 54 ].…”

“…It should be emphasized that the CCs of marine teleost and freshwater teleost are different in their structure and, in part, in their function [ 54 , 55 ]. It is well established that the principal function of the CCs in marine teleost is osmoregulation, but their physiological role in freshwater fish is still under discussion, and both the mechanism and cell sub-types vary amongst species [ 54 ]. More studies are needed to better clarify whether the differences observed in Na + /K + -ATPase expression would be species–specific or related to different functions of CCs in seawater and freshwater species.…”

Changes in Transcriptome and Ultrastructure Reveal Salinity Tolerance of Obscure Puffer Takifugu obscurus

“…At the same time, the number of mitochondria in the cells was more abundant than that in the freshwater treatment group and the tubular network system was much more developed than that in the freshwater treatment group. Mitochondria are closely related to the tubular network (Fridman, 2020). NKA on the tubular network system indirectly provides energy for excreting excessive Cl − from the body (de Fonseka et al, 2022).…”