Chefs know that when cooking fish, freshness is the most important factor. Yet for those of us without culinary credentials, it can be hard to know what to look for in the perfect pescatarian meal. In particular, experts say that noticing this color on a fish's gills can help you steer clear of fish that could make you more likely to develop serious foodborne illness. Read on to find out which color is a dead giveaway that something is wrong, and why you should never eat it.
RELATED: The One Vegetable You Should Never Eat Raw, CDC Warns.
If you notice purple or brown on a fish's gills, don't eat it.
ShutterstockWhen you buy whole fish at a market, one of the first things on your freshness checklist should be to check its gills. According to New York Magazine, these "Ought to be red; anything that looks a little more purple or (gasp) brown is a telltale sign of age."
Noelle Carter, Test Kitchen director for The Los Angeles Times, agrees that the gills are one of the easiest ways to spot an old fish. She adds that ideally, they should be a "bright red," a sign that the fish's oxygen-rich blood is flowing healthily through the capillaries in the gills as it breathes through the water. "As a fish ages, its gills will dull and start to turn brown," she adds.
Besides the gills being red, you'll also want to ensure that they have a suitable texture. Carter says that "slimy gills are a sure sign the fish is starting to go bad," while cooking experts from All Recipes add that the gills should be "damp" but never "sticky." Dryness in the gills can also indicate advanced age.
RELATED: Never Eat Microwaved Food Before Doing This, FDA Warns.
Purple or brown gills are a sign of oxidation, similar to color changes that occur in meat.
ShutterstockJust as steak or ground beef will begin to turn brown over time as it oxidizes, a fish's gills change colors from oxidation after being caught. "After several days, a fish's gills will become dark brown or even black in color, indicating that the fish's myoglobin has oxidized into metmyoglobin, which has a brick red-brown color," explains the cooking site Chef Steps.
In some fish, this process can also cause darkening or discoloration in the meat itself, says a report published in the Walailak Journal of Science and Technology.
Look for these other signs of freshness before buying.
Shutterstock/Alexander RathsBesides clean, healthy, red gills, experts say there are several other signs that your fish is at peak freshness. New York Magazine recommends checking the eyes, saying they should be "clear and bulging," never sunken or cloudy looking. Its scales should be bright and unbroken, and its skin may be slightly slippery, but never slimy.
Their experts further suggest touching the fish to assess its texture and buoyancy—a fresh fish should bounce back when you gently press on it. A fish with soft flesh that holds an imprint is old.
Finally, one of the easiest ways to tell if a fish has gone bad is to smell it. While a fish may smell "briney" or a bit like the ocean, it shouldn't actually smell fishy.
Be especially picky if you're in a high-risk group for foodborne illness.
ShutterstockWhile oxidation does not in itself present a danger, eating fish that's past its prime may increase your odds of food poisoning—especially if you happen to be in a high-risk group.
According to the Centers for Disease Control and Prevention (CDC), those at highest risk are individuals over the age of 65, children, pregnant women, and people with a compromised immune system. If you meet any of these criteria, you should avoid certain types of fish and be especially careful in how you store, preserve, and cook seafood.
RELATED: The CDC Just Released a Warning That You Shouldn't Eat This Right Now.
