1. You can also add 1 tsp. of mustard paste to the curry. This can be prepared by adding 1 tbsp. of water to 1 tsp. mustard seeds and blending it. This enhances the mustard taste in the curry. I avoid it because I find it very pungent. 2. Use of mustard oil really adds a lot to the flavour of the curry. But you can use olive oil or any other vegetable oil as substitute. 2. Buy fresh fish. You can use Catla (Bengal carp) or any other firm fish with white flesh like cod, halibut or similar. 3. The use of nigella seeds and mustard seeds in the tempering gives it a lovely taste. Also this curry is traditionally a bit runny so add water accordingly. 5. The nutrition values are for the air fryer version. For skillet version, each serve has 100 Calories more due to use of more oil.