Your nose should be your guide as you walk through the seafood aisle of the supermarket. If you catch the scent of a fishy smell that’s so overwhelming it makes you hold your breath, you should probably walk away. Generally, freshly caught fish doesn’t have a strong fishy odor, so if you’re getting one, it’s a strong indicator that it belongs in the trash rather than on your plate.

You see, as microorganisms break down the fat and proteins in fish, they create many smelly chemicals. One in particular, trimethylamine (TMA), is responsible for that characteristic fishy smell. However, when fish is fresh from the sea, these chemicals have yet to accumulate, so you shouldn’t get those odors. If they’re there at all, they should be mild. Admittedly, the presence of a smell doesn’t always mean it’s gone bad, as some kinds of fish, usually those from the ocean, may have a more intense fishy aroma. Still, it’s pretty reliable if you notice this along with other aging signs.

One Reddit user explains, “If the fish is fresh/good quality, it should smell like fresh ocean.” You may pick up hints of fresh-cut grass or seaweed as well. The slightly muddy aroma of freshwater fish from the bottom of the lake is another scent to note.