yes, this is possible but both the fish should be compatible to each other i.e. they should not possess threat o each other in other words they should be non predatory.
Most salt water fish will die if placed in fresh water.
The fish will get sick and die.
They die
they drown
they will die
It will die. It needs salt water
No, any additional animal put into a confined volume of water will increase ammonia levels and will therefore not keep water 'fresh'.
You could.... but I wouldn't recommended because it's not 100% healthy for the fish.
it would eventually shock the fish and kill them
me dont know
Fresh water
They would die because fress waterfish are meant for fresh water not salt water