Generally not seriously distinguish, as if they are similar. In fact, the mackerel is two kinds of fish, one is mackerel, one is Spanish mackerel, only because they look like the mackerel is called mackerel. If you want to see if the fish is fresh, you have to look at the meat to see if it's rotten, and use your fingers to press it. If the meat is elastic and doesn't have a pit, then it's fresh, and you have to look at the fish's eyes to see if it's bright and shiny, and look at the gills to see if it's black and smelly.