I defrosted it in the refrigerator 2 days ago, is it still good?
Did you purchase it frozen? If so, you should be fine. If not, it may or may not be. The best way to check is to smell it. If it smells overly fishy, then you probably don't want to eat it. If it smells fresh (like the sea) than it is probably fine. There are a lot of variables with this, so I would suggest if you have any real concern, I would just throw it out.
If it was frozen then you defrosted it and now want to refreeze it. The answer is no. It will lose its texture.