You may use any fresh fish. ** Cocum(Kudam Puli) is kind of tamarind used in Kerala. You can use ordinary tamarind also. Soak cocum in ¼ cup of water for 1 hour. Clean and cut fish into 1inch pieces. Grind coconut with all other ingredients except fish to a fine paste. In deep pan put ground coconut, kudam puly, and 2 cups of water and bring to boil. Reduce the heat and cook for 10 minutes. Put fish pieces and cook on medium heat till fish is done and gravy is thickened. Pour coconut oil over the curry and garnish with curry leaves. Serve preferably after 2 hours.