Rohu fish in mustard gravy is a popular Bengali dish that combines the delicate flavors of freshwater Rohu fish with a tangy and spicy mustard-based gravy. The fish is marinated in a mixture of mustard paste, turmeric, and salt, then pan-fried until golden brown. The gravy is made by blending mustard seeds, green chilies, and a few other spices with water. The fish is then simmered in the mustard gravy until cooked through. This dish is best served hot with steamed rice.