A quick explanation. Brackish water is the water that you would see at the mouth of a river where it empties into the ocean. It is somewhere between fresh water and salt water. The salt in brackish water is not table salt, it is the same salt you would use to set up a saltwater aquarium. I keep mollies which some people conside brackish but in their case they live fine in a straight freshwater setup so mine don't get any salt. From what others have said here, you are not in the same situation. If you decide to keep him it looks like you would actually need to create the right degree of brackish (saltiness) in your tank. I have no experience with these fish so I will refrain from specific advice about him. He is a cutie though.