Nanban Zuke — Japanese Sweet and Sour Fried Fish

Nanban zuke (南蛮漬け) is a Japanese dish of fried fish marinated in a sweet and sour sauce with vegetables. It’s one of those dishes that actually gets better as it sits — the fish absorbs the vinegar-based marinade and the flavours deepen over time. Make it the night before and it’s even better the next day.

The most common version uses aji (鯵, Japanese horse mackerel) or other small fish — whole or filleted, fried crispy and marinated in the sauce. This time I used kochi (コチ, flathead fish) that I had on hand. Kochi is a white fish common in Kyushu with firm flesh that holds up well to frying and marinating. Any firm white fish or small fish like aji, sardines, or smelt works perfectly for this recipe.

Nanban zuke — fried kochi fish marinated in sweet and sour sauce with carrot and onion

Ingredients (Serves 2–3)

150–200g aji (Japanese horse mackerel), whole small fish or fillets — or any small white fish such as sardines, smelt, or flathead
Salt, to season
1/3 carrot, julienned
1/2 onion, thinly sliced
1 tablespoon potato starch (katakuriko)
Vegetable oil, for frying

Nanban Sauce

2 tablespoons rice vinegar
2 tablespoons soy sauce
1 tablespoon sugar
3 tablespoons water
1/2 teaspoon dashi granules
Dried chilli pepper, to taste (optional)

How to Make It

Step 1: Prepare the Vegetables

Julienne the carrot into thin matchsticks and slice the onion thinly. Keep the cuts uniform so they cook evenly and look good in the finished dish.

Sliced onion and julienned carrot on a wooden cutting board

Step 2: Make the Nanban Sauce

Combine the vinegar, soy sauce, sugar, water, and dashi granules in a small saucepan. Add the chilli if using. Bring to a simmer over medium heat, stirring until the sugar dissolves. The sauce should smell sharp and tangy — that’s the vinegar doing its job.

Nanban sauce ingredients — vinegar, soy sauce and sugar on the kitchen counter

Nanban sauce simmering in a pot on the stove

Add the sliced onion and carrot to the sauce and simmer for 2–3 minutes until slightly softened. You want them to retain some crunch — don’t overcook. Set aside.

Sliced onion and carrot cooking in nanban sauce in a pot

Step 3: Prepare the Fish

The classic fish for nanban zuke is aji (horse mackerel) — small whole fish or fillets work well. I used kochi (flathead) this time, cut into pieces. Whatever fish you use, season lightly with salt and leave for a few minutes. Pat dry with paper towels — removing moisture helps the coating crisp up and prevents oil splatter. Dust each piece with potato starch.

Kochi flathead fish cut into pieces on a white plate

Step 4: Fry the Fish

Heat a generous amount of oil in a frying pan over medium-high heat. Fry the fish pieces until golden and cooked through — about 3–4 minutes per side depending on thickness. The potato starch coating crisps up nicely and helps the marinade cling to the fish later.

Kochi fish pieces frying in oil in a pan on the stove

Transfer to a wire rack or paper towels to drain the excess oil.

Fried kochi fish pieces draining on a wire rack

Step 5: Marinate

While the fish is still hot, transfer it to a container or bowl and pour the warm nanban sauce with the vegetables over the top. Make sure every piece is coated. The heat helps the fish absorb the marinade quickly.

Leave to marinate for at least 30 minutes. For the best flavour, refrigerate overnight — the fish soaks up the sweet and sour sauce completely and the whole dish comes together beautifully.

Fried kochi fish and vegetables marinating in nanban sauce in a pot

Step 6: Serve

Serve at room temperature or cold, straight from the fridge. Plate with plenty of the marinated vegetables and spoon the sauce over the top.

Nanban zuke served in a Japanese bowl with carrot, onion and sweet sour sauce

Tips from My Kitchen

Marinate while the fish is hot. Hot fish absorbs the marinade much faster than cold. Pour the sauce over immediately after frying.
It gets better overnight. Nanban zuke is one of those dishes where leftovers are better than fresh. Make extra on purpose.
Aji is the classic choice. Japanese horse mackerel (aji) is the most traditional fish for nanban zuke — use whole small fish or fillets. Sardines, smelt, and other small fish work just as well. I used kochi this time because that’s what I had.
Pat the fish dry before coating. Moisture prevents the potato starch from crisping up and causes oil splatter.
Adjust the sweetness and sourness to taste. Add more vinegar for a sharper flavour, more sugar for a milder one. Taste the sauce before adding the fish.

Where to Buy Japanese Ingredients

If you can’t find these at a local Asian grocery store, here’s what I use:

Soy sauce — use Japanese soy sauce for the right flavour
Dashi granules — adds depth to the marinade
Potato starch (katakuriko) — for coating the fish before frying

This post contains affiliate links. When you buy through links on this site, I may earn a small commission at no extra cost to you. I only recommend products I actually use in my own kitchen.

Nanban Zuke — Japanese Sweet and Sour Fried Fish