It depends on the kind of custard and the kind of fish fingers. Is the custard made from flour, egg, milk, sugar, butter... or is it instant "pudding" that is not really pudding? Are the fish sticks made from strips of real fish... or is it minced fish (which has scales and fins and all kinds of things thrown into the blender) that is formed into sticks and breaded?
But with ketchup there is no good quality. There is only sweet and tart and wet. Ketchup is what people use when they don't want to actually think about food, they just want to throw something on it and eat it fast and get on with watching their sitcom.