Depending on the type of eel, yes.
they usualy swim fast in both waters.
Obviously, since they are fish they will swim but Guppies (Lebistes reticularis) are freshwater fish and will die shortly after being placed in saltwater.
Dolphin's obtain water from their food, they don't actually need alot of fluid because unlike us, their skin is impermeable and they don't lose water by sweating.
saltwater freshwater saltwater freshwater
They contain saltwater and freshwater
they are both saltwater and freshwater
salt water weights more for a given volume than freshwater and that causes the increase in pressure
The Persian Gulf is saltwater, not freshwater.
Freshwater eels come in a few varieties such as the peacock eel, tiretrack eel, fire eel, etc. There is also what is called a freshwater moray, though I believe this eel to be mainly brackish and not truly fresh. Freshwater eels also include a species called the Polypterus, which include the Bicher which is commonly called the Dinosaur Eel. Freshwater eels are usually smaller and less aggressive than their saltwater brethren and generally spend alot of time buried into the substrate. There are eels from different locals offering choices to better suit the other tank occupants.
They live in freshwater. They eat stuff. They like to swim. They don't usually do well in saltwater.
freshwater
Freshwater