Steaming is ok with certain fish, but not really good for many types (ones that come to mind swordfish, catfish, salmon). I know people may steam those, but since the meat of most fish are so delicate steaming can really affect the texture. Swordfish (and others) become overly tough. It also depends on the size and thickness. Try your steamer with smaller pieces of say a light white fish first. If you are going to subject fish to a moist heat cooking method I would lightly poach them in a flavorable court bouillon (broth made up of various herbs and vegetables), you can also add an acid to the bath like lemon/lime or vinegar. Only my suggestions...have fun!