Flying Fish is a signature restaurant...requires 2 TS credits, really not worth it on the regular dining plan since you do not get the appetizer on regular dining plan even though you're charged 2 TS credits.
Last time we ate there, we were on the Deluxe dining plan, and were told we could choose whatever we wanted from each section, or we could order the fixed price menu...but the fixed price menu was all the cheaper choices so we just ordered from the regular menu. (appetizer is included on the Deluxe dining plan)
We have eaten at Kona, Les Chefs and CAptain's Grill on the regular dining plan, and yes the fixed price menu is available for the 1 TS credit on the regular dining plan. However, again the fixed price menu is limited choices and all of the items are the cheapest appetizer, the cheapest entrees and the cheapest desserts. So for example, you won't find the expensive steak offered on the fixed price menus...you're getting an appetizer, but only because they're offsetting the price by only offering cheaper options on everything.