The brassy chub (Kyphosus vaigiensis) is a sea chub and known as cá tà ma or cá dầm in Vietnamese. The word “tà ma” can be understood as “devilish”, “cunning”, “mischievous” or “ghostly” due to the fact the fish is hard to catch. The fish is found mainly in several Central Vietnam coastal provinces such as Khánh Hòa and Quảng Ngãi (in Lý Sơn island), and is considered as a delicacy food in those places.
One of the cooking methods of the brassy chub in Vietnam is to cook in canh chua, Vietnamese sour soup. The source of acidity is from the leaves of Aganonerion polymorphum (Vietnamese: lá giang). Alternately, the soup is cooked with common southern style by using tamarind paste, pineapple and taro leaf stalk (Colocasia gigantea). The soup can be made into a hot pot dish if served on a hot table stove.
When cooked as a hot pot dish, the dish is often served with a dipping sauce made from fish sauce and sliced chili pepper.
In a deep pan, sautee the sliced shallots with some cooking oil. Add tomato wedges and stir fry with a little water, so that the pan won't get burned. Add the brassy chub, flip the fish so that it absorbs some flavors.
When the fish flesh shrinks, add a big bowl of water, and bring it to a boil. Season with salt, granule seasoning, sugar, and add tamarind juice.
Increase the heat, add in turns taro leaf stalks, pineapple pieces, okra slices, and bean sprouts. Bring to a boil and turn off the heat.
The southern Vietnamese style of cooking sour soup requires reasonable amount of sugar, so the soup should taste sweet and sour.
Add some slices of cayenne pepper when serving.
Serve with rice.
In Vietnam, Kyphosus cinerascens (blue sea chub) is also recorded, so there could be some confusion with Kyphosus vaigiensis.