Effects of different salinities on the osmoregulatory capacity of Mediterranean sticklebacks living in freshwater

Abstract

Three‐spined sticklebacks (Gasterosteus aculeatus L.) of the Camargue region (Rhone delta, northern Mediterranean Sea) occupy coastal mesohaline lagoons and freshwater canals. In this study, the acclimation capacity to different salinities of a population living in freshwater canals was investigated. Freshwater (FW; 5 ‰) individuals were compared to fish acclimated for at least 2 weeks to brackish water (BW; 15 ‰) and seawater (SW; 30 ‰). Blood osmotic pressure and gill Na+/K+‐ATPase (NKA) gene expression of the α1 subunit and α1a and α1b isoforms were determined at these salinities. NKA protein expression in the gill ionocytes and the remodelling of these cells were also investigated through NKA immunolabelling and electron microscopy. Blood osmolalities of fish acclimated to FW, BW and SW were significantly different. Branchial NKA α1a and α1b expressions also differed, with a higher expression of NKA α1b in fish acclimated to SW. Gill ionocytes in fish acclimated to FW were located along the lamellae and at their base and appeared elongated, whereas these cells were restricted to gill filaments in fish acclimated to SW with a round shape. Finally, electron microscopy revealed three different types of apical structures for these ionocytes: a honeycomb‐like structure and a dome shape in FW, and deeply encrypted in SW. This study shows that ionocyte cell type and morphology, and gill NKA expression are salinity‐dependent. This branchial remodelling is directly linked to the physiological homeostatic status reached by the fish. It also highlights that sticklebacks of the Camargue region can rapidly acclimate to different salinities and can easily migrate between FW canals and mesohaline coastal lagoons.

Salinity‐dependent changes in branchial morphometry and Na+, K+‐ATPase responses of euryhaline Asian sea bass, Lates calcarifer

“…This study also observed ionocytes on the gill lamellae of the FW Asian sea bass, all of which were flat type I. Similarly, a large number of wavy‐convex (flat) type ionocytes were found on the gill lamellae in FW‐acclimated euryhaline fish (Duffy et al, 2011; Kang et al, 2017; Rind et al, 2017). This phenomenon is one of the mechanisms of reversible gill remodeling, in which ionocytes proliferate from the interlamellar epithelium up onto the lateral surface of the lamellae (Wood & Eom, 2021).…”

“…Lee et al (1996) This study also observed ionocytes on the gill lamellae of the FW Asian sea bass, all of which were flat type I. Similarly, a large number of wavy-convex (flat) type ionocytes were found on the gill lamellae in FW-acclimated euryhaline fish (Duffy et al, 2011;Kang et al, 2017;Rind et al, 2017). This phenomenon is one of the mechanisms of reversible gill remodeling, in which ionocytes proliferate from the F I G U R E 7 Average number of NKA immunoreactive cells (ionocytes) in the interlamellar epithelium of gill filaments (the length of each filament in the longitudinal section containing 15 pairs of lamellae) in SW, BW20, BW10, and FW groups as well as the cells on five lamellae in the FW group of Asian sea bass.…”

Morphological and physiological traits of Mediterranean sticklebacks living in the Camargue wetland (Rhone river delta)

“…As seen in the European seabass Dicentrarchus labrax and in sticklebacks, in SW a higher gene expression of the branchial NKA α1b isoform occurs compared to the NKA α1a isoform, these isoforms being involved in ion secretion in the SW‐type ionocytes and in ion uptake in the FW‐type ionocytes, respectively (Blondeau‐Bidet et al ., 2016; Rind et al ., 2018). At the protein level, NKA activity is higher in FW fish compared to SW fish.…”

The combined effects of microbial insecticides and sodium chloride on the development and emergence of Chironomus xanthus

“…The plastic boxes contained inorganic sediments (previously burnt at 500 °C for 5 h) and aerated American Standards for Testing and Materials (ASTM) medium. 42 Four solutions were made to prepare the ASTM medium: solution 1, 0.0381 g/L calcium bicarbonate (NaHCO 3 ); solution 2, 0.04914 g/L magnesium sulfate (MgSO 4 •7H 2 O); solution 3, 0.0016 g/L potassium chloride (KCl); solution 4, 0.0024 g/L calcium sulfate (CaSO 4 •2H 2 O). 200 mL was used from each solution 1, 2 and 3 and later 1.5 L of solution 4 in 20 L distilled water, pH 7.5.…”