In a medium bowl, combine smashed turmeric and water. Filter and get the extract of the turmeric. Set aside.
Put the catfish in a casserole, then pour-in water and vinegar.
Season with salt, black pepper then add the turmeric extract. Cover and let it boil for 5 minutes. Set aside.
In another pan, heat cooking oil. Saute garlic until brown. Then add the onion and tomatoes, cook until the tomatoes melt.
Then add the boiled catfish and cook for another 5 minutes.