Salamanders are semi-aquatic amphibians. Some live permanently under water, but most are terrestrial. The exceptions are the neotenic forms (ones that stay as "tadpoles" their entire lives, like axolotls) and the "giant salamanders" like the hellbender. So, unless you know that the species in question is one of the aquatic ones, in which case expect it to grow to at least 30 cm long, a salamander will need a mix of water and land in its tank.
I'm sure that some species will get along fine with fish of appropriate size and temperament, but salamanders are predators, so at least smaller fish are likely to be viewed as food. Conversely, some large fish tend to nip at curious or odd animals in the tank, like crabs, shrimps, apple snails, and most likely salamanders.
Personally, I wouldn't bother. Keeping amphibians and reptiles in captivity
is not the same as keeping fish, so you will need to
read up on the topic first.
Cheers,
Neale