Giving fish some lemon aid.

Acids. Bacteria. TMAO. And why Chinese restaurants have tanks of swimming fish.


Slices of fish and lemon1-Minute NomNom

Why do restaurants sometimes serve fish with slices of lemon? They give it a zesty tang for sure. But that’s not the only reason. Often, it can also be about acids, smells and how fresh the fish is.

Fish decomposes more rapidly than other meats. A major reason this happens is because it contains more trimethylamine oxide (CH₃)₃NO — TMAO for short. Once a fish is killed, bacteria attack and decompose it, producing trimethylamine N(CH3)3  — TMA for short. TMA is what gives the fish its “fishy” smell.


One way to get rid of the smell is to use lemon. Its acids help to neutralize the TMA.  Another way is to do what fishermen and fish suppliers often do: put it in ice. This slows down the bacteria’s decomposition.

Even better than lemons and ice is to eat fish fresh. Fish that were killed only a few hours ago do not have the “fishy” smell yet. No wonder Chinese restaurants keep their fish swimming around in tanks (see photo – click to enlarge), and catch and cook it only when we order.

Seafood market fish tank in Hong Kong

TMAO can also be found in other types of seafood such as molluscs and crustaceans.  Hence the lemon wedges and lemon sauces often served with them. Putting them in ice or keeping them alive till they are ready to be cooked — which is what you see in the tanks in the photo above — works well too.

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photos: in order – depositphotos/Taden1silvaeleungchopan

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