Filter feeder get their food by straining (filtering) it from water, most often sea water. Examples of filter feeders are: sponges, clams, oysters, barnacles, basking sharks, whale sharks...
Your water is lacking in Oxygen and needs to be replaced. Please do a water change ASAP. Then keep to the basic rules of sucessfull fish keeping. 1 inch of fish needs at least 1 gallon of water. :-...