The legendary fish with the * are fish you won't be catching until you're level 50. I'd say first check to see if there's any recipes or leves that use the fish you fished up (You can see that information easily by searching at ffxiv.gamerescape.com). If it's used in a recipe in something, you can likely sell it on the market boards when you have a retainer. Or you can use it for crafting yourself, or turn them in at the leves for yummy xp.