There are several kinds of Sushi, The fish isnt the problem its the rice, there are Sushi that you eat just the fish and no rice.
The point here is not Sushi vs Gefilte, In fact I know people who hate any kind of fish, the point here is not to claim you must eat a certain food “L’Kavod Shabbos” if you find it digusting. No normal Rav is going to tell you to eat it anyway because they should be smart enough to realize eating something you cant stand most likely wont get you to like it, but you will likely become repulsed even more from it (and perhaps shabbos in general if you associate shabbos with food you hate)