This is a debated topic. There are both pros and cons. Though oxygen is very important, too much can be deadly for a fish. The finer the bubbles the more likely your fish may get air bloat. Also adding an air stone increases the CO2 gas exchange process increasing the pH in the water. Marine fish like basic water. Also in a reef tank too much oxygen can kill coral. Normally filter systems creates enough oxygenation for a tank to where an air stone is not needed. If you want air bubble for a decorative effect try to get something tha doesn't create a fine bubbles.