a simple statement, warding off those who think metriods are cute, and look hungry. metroids feed off of the life forces of other living creatures. feeding them your rations might reek havoc upon thier specialized digestive systems. also, if a metroid sucessfully recieves energy from any meal, it grows in size and strength. so by feeding a metroid in a holding tank, you are helping it escape.
if you are stupid enough to want to feed a metroid, why dont you just jump in the tank , and let it eat you?