For the greatest omega-3 benefit buy the fattiest fish. Try mackerel, anchovies, herring, sardines, salmon, tuna and turbot. Frozen and canned are OK, the USDA says. Posted on January 7, 2021 by justfoodpictures For the greatest omega-3 benefit buy the fattiest fish. Try mackerel, anchovies, herring, sardines, salmon, tuna and turbot. Frozen and canned are OK, the USDA says.