Marinate the fish with turmeric and salt.
Dissolve the remaining turmeric powder and red chili powder in a little water and keep aside.
Heat oil in a pan, shallow fry the fish. If the ilish is indeed very fresh, you need not fry it.
To the same pan, add the remaining oil, when smoking hot, throw in the nigella seeds and green chillies and allow them to splutter.
Now add the turmeric - red chilli paste, cook for a couple of minutes till oil starts releasing from the masala.
Lower the flame and gently pour in the milk, allow to simmer.
When the gravy has reduced to almost half, add the fish and adjust seasonings. Cook over a low flame for a further 3-4 minutes, doodh ilish is ready.
Serve hot with white rice.