Heat a large saucepan of water to 61°C (142°F). Sprinkle the fish with salt and place each in a small vacuum-seal or zip-lock bag with 2teaspoons oil. Follow the Masterclass on sous-vide cooking and cook the fish for 14 minutes. Remove from the water and rest in the bags for 2 minutes. Remove from the bags, reserving the juices. Serve immediately.