Remodeling of gill and kidney epithelia in puffer fish (Tetraodon biocellatus Tirant 1885) acclimated to water of varying iron content

Puffer fish (Tetraodon biocellatus) were acclimated to ion-poor water (IPW), freshwater (FW) or seawater (SW) and alterations in gill ionocyte and kidney tubule structure and abundance, as well as changes in gill and kidney tight junction (TJ) mRNA were examined. Gill ionocyte abundance increased in fish acclimated to IPW and SW and significant differences in ionocyte exposure were noted. The presence of a putative ionocyte that was voluminous and NKA-rich but was "mitochondria-poor" is described. Alterations in surface area and tubule numbers were observed in proximal and distal tubules in response to environmental ion levels. mRNA encoding for the claudin-3, -8 and -27 TJ protein families (designated Tbcldn3a-d, Tbcldn8a-d and Tbcldn27a-d) were examined for presence and abundance in the gills and/or kidney. The data highlight the importance of remodeling both the transcellular and paracellular transport pathways in the gills and kidney of fish in response to altered environmental salt content.