Mackerel is an oily fish, it is a rich source of Omega-3 fatty acids, there are two species available at our side now, one is Pacific Mackerel (Scomber Japonicus), another is Spanish Mackerel(Scomberomorus Niphonius) Pacific Mackerel is frozen in whole round block or cut into fish fillets, Spanish Mackerel is cut into fish fillets or steak.