they usualy swim fast in both waters.
Some can, most can't. Some that can are salmon which swim up rivers to spawn as adults and certain sharks, like the bull shark, that can survive lengthy periods in freshwater.
Depending on the type of eel, yes.
Bull sharks and River sharks are the only true sharks that live in fresh water, although there are several other species of fish that sometimes have "shark" in their informal names.on the lighter side...only wimpy sharks
Obviously, since they are fish they will swim but Guppies (Lebistes reticularis) are freshwater fish and will die shortly after being placed in saltwater.
No the salmon and bull and sometimes the blue shark swim in freshwater sometimes.
No. Saltwater is denser than freshwater, and your body will be more buoyant. You will be higher in the water and, therefore, will have less water resistance. You will swim faster, but will not get as good a workout as in freshwater.
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.
salt water weights more for a given volume than freshwater and that causes the increase in pressure
they swim faster and hide in small places
If they are strong they can swim faster after prey, get where the food is faster, and get faster to where the shark the can mate with is.
Yes, they can swim into freshwater rivers.
yes, it makes the shark lighter