Potatoes that smell like fish are almost certainly starting to rot. The fishy odor comes from chemical compounds called amines, particularly trimethylamine, which bacteria produce as they break down potato tissue. This is the same compound responsible for the smell of old seafood. If your potatoes have reached this point, they are not safe to eat.
What Causes the Fishy Smell
When bacteria colonize a potato, they begin digesting its cells and releasing a cocktail of volatile compounds including aldehydes, ketones, alcohols, hydrogen sulfide, and amines. Trimethylamine is the standout culprit behind a distinctly fishy scent. In small amounts, the smell might be faint or just “off.” As decay progresses, it intensifies and can become overwhelming.
The most common bacterium involved is one that causes a condition called bacterial soft rot. It thrives in warm, moist environments and can spread from a single infected potato to an entire bag. The rot often starts inside the potato or at a wound site (a nick from harvesting, a bruise from handling) and works outward, meaning a potato can be deteriorating internally before you notice anything on the surface.
How to Spot a Rotting Potato
The fishy smell is often the first warning sign, but there are visual and textural clues too. Affected potatoes develop small to large circular lesions on the skin that look sunken, tan or brown, and water-soaked. Press gently and the flesh underneath feels soft or spongy rather than firm. In more advanced cases, an amber-colored liquid may ooze from the rotting areas. The internal tissue turns white to tan and breaks down into a paste-like consistency.
A different type of rot, sometimes called leak, produces tissue that looks brown or gray with a uniform, watery texture. The margins of the decayed area are sharply defined and darker in color. These potatoes tend to develop a sour odor rather than a fishy one, and they eventually dry out into a thin, papery shell. Both conditions mean the potato should be thrown away.
Storage Mistakes That Accelerate Rot
The most common reason potatoes go bad prematurely at home is improper storage. Potatoes are still alive after harvest. They continue to respire, consuming oxygen and releasing carbon dioxide and moisture. When they’re sealed in a plastic bag with no airflow, oxygen levels drop and the potatoes shift into anaerobic respiration (essentially fermentation). This creates off-flavors, foul odors, and conditions where rot-causing bacteria flourish.
Heat makes everything worse. A warm kitchen counter or a spot near the stove dramatically shortens shelf life. Moisture is equally problematic. If potatoes sit in condensation or their own trapped humidity, the wet surface becomes a breeding ground for bacteria. Even a single potato that has started to rot releases moisture and gases that can trigger decay in its neighbors, which is why one bad potato really does spoil the bunch.
How to Store Potatoes Correctly
The ideal storage temperature for potatoes is 45 to 50°F (7 to 10°C), which for most people means a cool basement, garage, or pantry rather than the refrigerator. Commercial potato storage facilities hold tubers at 50 to 55°F with high humidity during a curing period to let any skin damage heal, then lower the temperature gradually. You don’t need to replicate commercial conditions exactly, but the principles apply: cool, dark, and ventilated.
Use a paper bag, mesh bag, or open cardboard box rather than a sealed plastic bag. The goal is airflow. Keep potatoes away from onions, which release gases that accelerate sprouting. Check your potatoes every few days and remove any that feel soft, show dark spots, or smell off. If you bought a bag and one potato is already rotting, inspect every potato in the bag individually. Wipe down any that were touching the bad one and let them dry before storing them again.
Are Fishy-Smelling Potatoes Dangerous?
Yes. Potatoes that have reached the point of producing a fishy or foul smell should not be eaten, even if you cut away the visibly rotten parts. The bacteria responsible for the odor may have spread beyond the area you can see, and the chemical byproducts of decomposition penetrate further than the soft tissue. Rotting potatoes also produce toxic gases. There are documented cases of people being fatally overcome by the fumes from large quantities of decaying potatoes in enclosed spaces like basements or cellars.
Potatoes also naturally contain a toxic compound called solanine, which increases when tubers are damaged, green, or decaying. Solanine is not what causes the smell (it has no odor), but a rotting potato may have elevated levels of it alongside the bacterial toxins. The bottom line: if a potato smells like fish, throw it out. If multiple potatoes in a bag smell off, discard the entire bag and ventilate the area where they were stored.