Clean and cut fish into bite size pieces. Heat a pan and roast coconut, urid dal, channa dal cumin seeds and red chilly till coconut is browned. Grind this to get a fine paste. Boil 2 cups of water tamarind paste, turmeric powder and salt in a deep pan. Add ground coconut and enough water, reduce heat and cook for 10-15 minutes. Put fish pieces into the gravy and cook till fish is done and gravy is thickened. Serve hot with rice.