Wash the ilish pieces and pat them dry. The trick with Ilish is to not wash it too much. They say the taste goes away if you wash ilish too much.
Rub the pieces of the fish with 1/2 tsp of turmeric powder and a little bit of salt and keep aside.
Cut the brinjals length wise into quarters. The length of the brinjals should preferably be as long or probably longer than the size of the ilish pieces. Of course we are not talking about cooking khoka or baby ilish (that would be a crime). Each brinjal would give you 4 or 5 slices at the most.
In a frying pan or a kadai, take 2 tbsp of mustard oil. When the oil has reached a smoking point, release the fish pieces in the oil and lower the temp. We want the fish very lightly fried. Just half a minute of each side would be enough.
Use the slotted spoon to take the fish out of the oil and keep them very gently on a plate.
In the same oil, add one dried red chili, nigella seeds and the fenugreek seeds. When they splutter, add the brinjals. Sprinkle the balance turmeric powder and a little bit of salt and fry the brinjals in that mustard oil.
The brinjals will within minutes soak up the oil. So reduce the temperature and cover and cook the brinjals.
It takes about 7 to 8 minutes for the brinjals to become soft. Then add about 2 cups of water. Slide the fish pieces in the water. Keepng the tempetarure at a medium, let the gravy simmer for sometime. Add salt as required.
Add slit green chilies and finally when oil starts to float on top of the gravy, turn off the heat.
Serve it with steamed rice.