Yes, absolutely.  Rice cookers usually has accompanying steamer basket.    If you are steaming fish using rice cooker, pour water on your rice cooker bowl, about 6 cups.  Place steaming rack or steamer basket on top which will serve as the placeholder of your fish.    You can now press the steam button of your rice cooker if it is a multi-cooker.  However, if it has only the rice cooking function, use that rice cooking button and let the water boil to steam the fish.    Just take note of the size of your fish and rice cooker.  The circumference of your rice cooker should be able to accommodate the size of your fish.