Dried and Salted Fish Fillets (e.g. cod) Sous Vide
The purpose for salting fish is to cure it (originally for preservation). It does not need to be cooked. The reason for soaking and/or boiling salted fish is to remove the excess salt and to rehydrate the fish for consumption. Sous vide probably doesn't make sense in the preparation of salted fish, but I'd be curious how it comes out. You should soak to remove salt to taste. Be sure to taste the inner flesh when testing for saltiness. 

For sous vide preparation, I would suggest soaking in cold water to remove enough salt and then cooking at a lower temperature. 50°C is a good temperature, but you can go even lower for salted fish. You might experiment as low as 40°.