add oil to pan,fry onions n green chilli,add turmeric......add rohu pieces,salt n chilli powder,then add tamrind puree,let it cook for 15 min.........dont add cold water in the middle of the procee add required amount of water to tamrind puree.........then cover it with a lid,let that cook....... .important thing.........dont mix the curry with spoon or spatula while cooking,just hold the bowl revolve it with ur hands in circular motion and make sure it was mixed........... ,once u observe the fish piece is cooked...... make a paste of corainder seeds,cumin and garlic add water for fine paste....... add this mixture to the pan and let this boil.......... so that ur dish is ready...finally add some corainder leaves.......taste for salt n chilli powder..to add some if necessary