Marinating tuna steaks or fish does not require the same length of time as it takes to infuse flavour into meats. Ezilon Infobase and Fishing Loft recommend just 20 minutes and no longer than 30 to marinate tuna steaks.
Depends On Recipe's Marinade
Recipes for tuna steaks can specify different marinating times. For instance, a recipe for soy-glazed tuna steaks on the BBC Goodfood website calls for one hour because the base of the marinade is soy sauce rather than an acidic ingredient. According to the Fishing Loft, acidic marinades begin to cook the tuna after 30 minutes.
Marinate tuna steaks quickly to infuse flavour. Follow the recipe guidelines for the correct marinating time specific to your dish. If you are not following a recipe and using acidic ingredients, marinate the tuna for the recommended time of 20 minutes or no longer than 30 to avoid cooking the tuna in the marinade. If you are using a nonacidic marinade, you can leave tuna steaks in it up to one hour.