Abstract
Mozambique tilapia (Oreochromis mossambicus) is a kind of freshwater teleost whose natural habitats are in fresh water of southern Africa. Milkfish (Chanos chanos) is a kind of marine teleost widely distributed throughout the tropical and subtropical Indo-Pacific. Both Mozambique tilapia and milkfish are euryhaline teleosts and can survive in a broad range of salinity. Since the activity and Na+ and K+ affinities of branchial Na+/K+-ATPase (NKA) changed with environmental salinities, it is suggested that the difference may be due to the switches of NKA α-subunit isoforms. The kidney is another important organ responsible for ion-regulation in teleosts. However, few studies addressed on the mechanisms of ion-regulation in kidney. In order to compare the ion-regulation mechanism between two euryhaline teleosts from different primary natural habitats in response to salinity challenge, this study focus on the switches of renal NKA α-isoform proteins between tilapia (Oreochromis mossambicus) and milkfish (Chanos chanos). Mozambique tilapia and milkfish were acclimatized and reared in seawater (35‰) and fresh water, respectively, for more than two weeks before sampling. In Mozambique tilapia, the protein abundance of renal NKA α-subunit, α1-, and α3-isoform in seawater-acclimatized fish was significantly higher than in freshwater acclimatized group. On the other hand, the α2-isoform was significantly lower in freshwater acclimatized individuals. In freshwater acclimatized milkfish, the protein abundance of renal NKA α-subunit and α1-isoform was significantly higher than in seawater-acclimatized group. As for α2- and α3-isoform, the protein abundance reveals no significant difference between different salinity groups. In conclusion, the protein abundance of renal NKA α-subunit was significantly higher in SW-acclimatized Mozambique tilapia and FW-acclimatized milkfish, and the protein abundance of renal NKA α-isoforms was influenced by environmental different salinities. In addition, the switches of renal NKA α-isoforms, especially α1-isoform, may be involved in the mechanisms of ion regulation in FW- and SW-acclimatized Mozambique tilapia and milkfish.
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