Crab sushi doesn't require fishing... but to farm crabs.
Well, keep in mind you can't be reactive about black soles. It takes time skilling fishing to the point you can seriously consider fishing these. So people willing to fish doesn't mean they can fish.But I think sushi doubling in price, or more, will have a much larger impact on the game than reraise items. Sure there will be more players willing to go fish soles, but will that be enough to satisfy the demand ? I doubt it.
Seeing a spike for two weeks doesn't mean the price will stay high forever.