Are there any genera of aquatic animals that have two species living in different types of water? Ie: one species in freshwater, one in saltwater?
I know there are some genera of fish and other organism that can survive between fresh and salt water like salmon and tiger sharks \[i remember hearing something about tiger sharks swimming up rivers for short periods of time\]. But im more talking about like animals that show specific adaptations to one type of water or environment and cannot really switch.
For context: I am trying to design a god of water bodies for a dnd world. I was thinking about having her split between freshwater and salt water with some noticeable differences like size of apperance, temperment, clothing, anotomy etc. But I want to be able to base it off of animals that live in such conditions as if she has adapted and been changed by the body of water she is associated with when you meet her.
Do any of you know anything that could fit or any differences between the two i could add?