Ok im feeling more at ease with eating whole sardines after reading this:
Good quality sardines should have the and gills removed before packing. They may also be eviscerated before packing (typically the larger varieties), or not; if not eviscerated they should be free of undigested or partially digested food or fecesFecesFeces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus during defecation.-Etymology:...
(accomplished by holding the live fish in a tank for long enough that their digestive systems empty themselves).
I always was suspicious of dark marterial in the little fishys!!