Pa daek (padaek; pla ra in Thai and Isan) is the fermented fish of Laos and northeast Thailand: small freshwater fish packed with plenty of salt and roasted rice or rice bran and left for months until they break down into a thick, pungent, deeply savoury paste with a cloudy liquid on top. It’s the seasoning behind Lao tam mak hung (green papaya salad), the chilli dip jaew, soups, curries and dipping sauces. Unlike clear Thai or Vietnamese fish sauce, which is made from sea fish and filtered, pa daek is chunky and earthy. Cambodia’s prahok is a close relative.
The Liver Fluke Problem
Pa daek is made from freshwater fish – often small carp-family (cyprinid) fish – and in the Mekong region those fish can carry the larvae of the liver fluke Opisthorchis viverrini. Eating raw, fermented or undercooked cyprinid fish infected with the fluke causes chronic inflammation of the bile ducts, scarring and a higher risk of bile-duct cancer (cholangiocarcinoma), which is far more common in Southeast Asia than elsewhere (Hughes et al., 2017). The International Agency for Research on Cancer classes infection with O. viverrini as carcinogenic to humans, Group 1 (IARC Monograph 100B). A Thai meta-analysis found fluke infection and eating raw cyprinid fish among the strongest risk factors for the cancer (Kamsa-ard et al., 2018), and infections remain common across the Greater Mekong Subregion (Sripa et al., 2021).
Salting and fermentation don’t reliably make the fish safe. Heat does: in a Thai study, boiling infected fish at 90°C or microwaving for at least 5 minutes killed the fluke larvae, as did freezing fermented fish at −20°C for 48 hours (Sripan et al., 2017). Boiling pla ra for 5–30 minutes also lowered its nitrate and nitrite content and reduced liver inflammation and scarring in fluke-infected hamsters (Artchayasawat et al., 2023). As the researchers put it, cooking fish is the best way to avoid infection (Sripan et al., 2017).
How to Use It Safely
- Buy it rather than make it. We don’t give a home fermentation method: it’s a months-long ferment of raw whole fish, and the main hazard can’t be seen or tasted.
- Cook it. If you can find products labelled cooked or pasteurised, choose those; otherwise boil pa daek with a little water for at least 5 minutes before using it in uncooked dishes such as papaya salad or dips (recipe card below). In soups, curries and stews, simmer it with the other ingredients.
- Use a little. It’s very salty; a spoonful seasons a whole dish.
- Raw freshwater fish dishes carry the same fluke risk; cook the fish.
For fish sauce made from sea fish, see our fermented fish sauce guide, and for Italy’s anchovy version, colatura di alici.