The Mekong and Its Fish

The Mekong runs along much of the eastern boundary of Thailand and drains the Khorat plateau of Isan through its tributaries, so that the river and its seasonal waters have long supplied the fish on which the cooking of the middle and lower reaches depends. Alford and Duguid in Hot Sour Salty Sweet place the preservation of fish by fermentation along the middle and lower Mekong and in central and southern Thailand, a practice shared by the peoples of Thailand, Laos, Cambodia and Vietnam.

The fish of the Mekong are eaten fresh, grilled and preserved, and it is preservation that underlies the cooking of the river's middle and lower reaches. Alford and Duguid describe the fermented fish of the region as pieces of fish lying in a brine, often thickened with rice bran, of which both the fish and the liquid are used. One preparation travels under several names: prahok among the Khmer, padek in Laos and Isan, mam in Vietnam, and pla raa in Thailand. Each is strongly flavoured, and each requires fish; salted and fermented fruits or vegetables may approximate other salty seasonings, but they cannot take its place. In outline the method is plain. Salted fish are packed into an earthenware jar, often with toasted rice or bran mixed through, and left to ferment. It allows a catch to be kept beyond the season of abundance, and Alford and Duguid observe that it also supplies amino acids to a diet built on rice and vegetables with little animal food. The preserved fish is therefore a necessity of the table as much as a seasoning. Fish sauce, nam pla in Thai, derives from this paste. It is the pale liquid given up by heavily salted, pressed fish as they ferment, and the Vietnamese nuoc mam, meaning liquid from mam, preserves that origin in its name. Thai and Cambodian sauces are generally gentler than Vietnamese ones, and any sauce may range from faintly smoky to markedly pungent. A good bottle names no sugar among its ingredients and keeps almost indefinitely in the cupboard without refrigeration. As a rough measure, one tablespoon of fish sauce stands for one teaspoon of salt. The fermented fish itself may replace fish sauce in many dishes, added with caution and tasted as one goes, for its strength is greater. It is sold in jars in Southeast Asian groceries, labelled for example preserved gray featherback fish or preserved mudfish. The markets of the region also sell fish grilled with salt, to be carried home and eaten with rice and other dishes, a method the home cook can follow over a grill. Whole fresh fish are likewise rubbed or filled with a flavouring paste, wrapped, and grilled or baked. Salt, fire and fermentation together keep and season the river's catch.

Fermented fish gives a salty, deeply savoury and often pungent note, stronger than that of fish sauce, and the cook should add it with care and to taste. Fish sauce supplies salt and savour in a milder form, ranging from slightly smoky to very pungent, and is the essential seasoning and condiment of much of Southeast Asia. Both are eaten with rice and the vegetables of the table, and salt-grilled river fish takes the same place beside them.