Sardines are an inexpensive source of protein and healthy fats. They are available fresh, frozen, and canned. Always eat your sardines with skin and bones to provide the most calcium. and protein.Unlike other omega-3-rich fish, they are low in mercury and other containments. They are small in size and have a short life span which means they don’t have as long to accumulate mercury as larger fish like tuna. They also eat plankton which is relatively low in mercury.