Koi — the climbing perch — is a small, bony freshwater fish that lives in the ponds and canals of the Bengal delta and is known for its ability to survive out of water for hours, which means it arrives at the market alive. Bengalis have been cooking it this way — fried hard in mustard oil until the skin blisters and chars, then finished in a sharp sauce of mustard paste and green chilli — for as long as anyone has written down recipes in this part of the world.
It is sold by roadside vendors and eaten with panta bhat in the morning, or with hot rice at midday. Outside Bengal, koi is almost entirely unknown.
Zone: River Delta
SOURCE: Translaed from a recipe shared by a home cook from Barishal district, Bangladesh, on a Bengali-language cooking forum, 2017.
LOCAL NAME: তেল কই
INGREDIENTS
- 4 koi fish (cleaned and scored (or substitute — see notes))
- 1 tsp turmeric
- 1 tsp salt
- 4 tbsp mustard oil
- 3 tbsp yellow mustard seeds (soaked 2 hours)
- 1 tbsp black mustard seeds (soaked 2 hours)
- 3 green chillies (slit, plus 2 extra for finishing)
- ½ tsp nigella seeds (kalonji)
- ½ tsp turmeric
- 1 tsp salt
- 100 ml water
METHOD
- Rub the koi fish with turmeric and salt. Set aside for 15 minutes.
- Grind the soaked yellow and black mustard seeds with 2 of the green chillies and a splash of water to a smooth paste. It should be pungent and slightly bitter.
- Heat the mustard oil in a wide flat pan until it just begins to smoke. Reduce to medium-high. Fry the fish for 4–5 minutes per side, pressing gently with a spatula, until the skin is deeply blistered and dark in patches. Remove and set aside.
- To the same oil, add the nigella seeds and remaining green chillies. Allow to splutter for 20 seconds.
- Add the mustard paste, turmeric, salt, and water. Stir and cook for 2 minutes until the raw smell softens.
- Return the fish to the pan. Spoon the sauce over them. Cover and cook on low heat for 8 minutes until the fish is cooked through and the sauce has thickened slightly.
- Serve immediately over steamed white rice. The sauce should be sharp, thin, and vivid yellow.
NOTES
UK adaptation: Fresh koi fish almost impossible outside specialist Bengali fishmongers — try Whitechapel or Green Street markets. Frozen koi occasionally available. Best substitute is small whole tilapia or red snapper, scored and fried the same way — the texture is different but the preparation holds. Mustard oil and mustard seeds from South Asian grocers.
US adaptation: Fresh koi very occasionally available in Bengali community markets in New York and New Jersey. Frozen from specialist South Asian fishmongers. Tilapia or small whole red snapper as substitute. Mustard oil from Patel Brothers or Indian grocery stores.
Cook’s note: The hard frying stage is what makes this dish — the blistered skin is not incidental, it is the point. Do not rush it or use too low a heat. The fish should colour deeply before the sauce goes in.