Fish that can live in both saltwater and freshwater are called “euryhaline” species. They can handle big changes in salinity by actively controlling how much water and salt moves in and out of their bodies through their gills, kidneys, and specialized salt-transport cells. This ability lets them move between rivers, estuaries, and the open ocean—or live in brackish “in-between” water for long stretches.
Salmon are famous for hatching in freshwater, migrating to the ocean to grow, and returning to freshwater to spawn. Their physiology “switches modes” as they move between environments, helping them avoid dehydration in saltwater and water overload in freshwater.
Many eels do the reverse: they spend much of their lives in freshwater and migrate to the sea to reproduce. Like salmon, they rely on strong osmoregulation to make the transition.
Striped bass commonly move between coastal saltwater and freshwater rivers. They often use brackish estuaries as feeding and staging areas, especially during seasonal migrations.
Although they’re sharks rather than bony fish, bull sharks are well known for traveling far upriver and thriving in freshwater for extended periods. Their kidneys and other systems help them retain salts that would otherwise be lost.
Most aquarium and wild fish are “stenohaline,” meaning they’re built for a narrow salinity range and can be harmed quickly by sudden changes. Euryhaline species either migrate gradually through brackish areas or have broad tolerance that protects them during shifts in salinity.
For a longer list and deeper details on how these fish adapt, visit the full guide: https://monumena.com/what-fish-can-live-in-both-saltwater-and-freshwater/.
For Fish That Live in Saltwater and Freshwater (Euryhaline), the best answer depends on fit, material, care instructions, and how the product will be used day to day.
Yes. Many species thrive in brackish water, especially those that naturally inhabit estuaries; others can tolerate it only with slow, careful acclimation.
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