Sardines tend to conjure up images of cheap meals from tin cans however fresh sardines are a delicate, delicious fish very high in omega 3. Sardines come from the herring family and pilchards are the same species of fish, just slightly larger.
Sous vide is a very useful tool when cooking small fish such as sardines and pilchards as the low temperature ensures that the fish does not over cook and the bag locks in moisture that would be lost in traditional cooking methods. The controlled temperature and cooking period give a consistent result every time. Ask your fishmonger to butterfly the sardines for you, or alternatively read this How to butterfly sardines guide.