I understand what your trying to say, it's just that your inconsiderate of the animal and it's best environment. I would guess your not any older than 16. When the animal is suppose to live 30 years old, and it dies at 15-20 thats not good.
obviously you don't understand. I'm saying that most brackish fish NEED brackish. But SOME won't be effected adversely. Alligator gars for example can live in brackish and fresh water without suffering unduly. ( I realize AG are found mainly in fresh water it was just an example.)