If it's a true balsamic vinegar, it will be too sweet for the fish. The good stuff is aged for a very long time in oak barrels (I think it's oak) and is very syrupy and more sweet than vinagery. It's not much used in cooking, but rather is used as a condiment.
In any case, a more acidic vinegar can tighten up the meat protien, and at least partially "cooking" the fish. Fish cooked with vinegar is common in Phillipino cuisine.
There are a number of balsamic vinegars out there that are thin and that have overtones of wine or grape. They are great to use for cooking, or making salad dressings.
And for the record, there are a good number of people that believe salt water fish is parasite free and can be eaten raw, while fresh water fish contains parasites. While fresh water fish can have harmful and dangerous parasites in them, including taperworm, so can saltwater fish. Restaurants ensure the safety of their patrons by freezing the fish to about -15 degrees F. for many hours (I.C., could use your help here as I don't know the timing for this), which kills any parasites residing in the fish.
Just sharing info.
Seeeeeeeya; Goodweed of the North