i rescued an oscar from someone who was keeping him in a 20 gallon tank. he had fin rot, and one of his fins is about halfway gone. will it ever grow back?

as long as there is still some of the fin left there is a good chance that they will grow back. what you need to do is make sure your water is in pristine condition ammonia and nitrites at zero and your nitrates dont go above 30 ppm and you should be fine.

the fin has stopped rotting. ive had him for about four months, but it just doesnt seem to be growing back. how long does this process usually take?

Fin should grow back entirely.

as long as the base of the fin is not damage, it grow back slowly.
which part of the fin/s is/are damage?

those parrot fish that grow heart shape had been tampered, the tail
is removed in a heart shape shear to make them look like that.
CRUEL..... :angry: :angry: :angry: :angry: :angry: :angry:

its just the tip of the fin, about halfway down. there was a white spot at the base at first. but that went away after a week or two. it doesn't affect his swimming, he actually jumps all the way out of the water to get food from my hand, so im pretty sure there isn't a problem there.

a perfect sign to recovery...just keep the water in A-1 condition
and you will be fine...