Rabbi Ovadia Yosef, in his 51st volume of Responsa, and deals with the Ashkenazi tradition of eating gefilte fish on the Shabbat.
He explains that
...one of the reasons behind the invention of the gefilte fish was a stiffening of the "borer" law (one of the 39 labors prohibited on Shabbat involving the separation of two or more food items that are mixed together [actually separating “Pesolet” (refuse, or undesirable substance) from “Ochel” (food)]). The preparation of gefilte fish involves finely mincing carp, including its fine bones. "The cheap and abundant carp has small spiky bones and many Ashkenazi arbiters found the gefilte fish cakes to be a simple solution" to the "borer" prohibition of removing the small bones...
The Rabbi's solutution? Simple - cancell out the problem:
In the book, the rabbi permits the removal of the carp's small bones on Shabbat, explaining that this does not institute a violation of the "borer" law. This means that Shabbat may be stripped of its weekly dose of gefilte fish, in favor of whole fish.
Actually, we Ashkenazim love gefilte fish so there is no way we're giving it up. Not for all the Sefaradi pilpul in the world.