In December and January, around the time when the moon is waxing or full, Cambodians get ready to make prahok, the pungent-smelling, much-loved fermented fish paste used in most Khmer dishes.
As water levels in the Mekong River and the Tonle Sap lake and river slowly start to drop at the end of the rainy season around November and flooded forests begin to drain, the trey riel, or Siamese mud carp in its official name, wait for the moon to shine bright and then start their mass exodus.
The beginnings of their journeys vary from one area of the country to the next. At Mok Kampoul district in Kandal province, they migrate just before the moon is full. Near Kratie town, the small fish leave during full moon. And in Sambor district in Kratie province, the fish wait for the moon to wane before swimming upstream, according to a World Fish Center study.
Everywhere, however, Cambodian fishermen, relying on centuries-old knowledge about these events, are ready.
During the frantic week or so that follows the brightest lunar phase, fishermen catch a staggering 7,000 to 8,000 tons of fish, said Nao Thuok, director general of Cambodia’s Fisheries Administration. “This season, the fish used to make prahok will increase by more than 20 percent” over last season, he said.
Mr Thuok said he expects this year’s total catch during the two periods of fish migration, at the end of December and at the end of January, to reach 15,000 to 16,000 tons, amounting to roughly 20 percent of the annual inland fish catch.
As soon as trey riel is hauled in, Cambodian families across the country travel to the nearest fisheries area to clean and pot the fish on site with large amounts of salt: around 400 grams of salt per kilo of fish.
Ms Chanthet, a 43-year-old woman from Kompong Cham province’s Prey Chhor district, said fish prices were lower than last season. They have dropped from 2,000 riel, or $0.50, last year to 1,200 riel, around $0.30, per kilo, she said.
Ms Chanthet, who did not wish to give her family name, uses prahok year-round and would be unable to cook without that fish paste because “it makes the rest of the food taste good,” she said. “We are farmers, we need prahok to put in our food. Prahok bought at a market is not good, it has too much salt,” which is why she has bought 50 kilograms of fish so that she can make prahok for her family herself.
While trey riel and prahok are central to Cambodian livelihoods and cuisine, the future of fish species in the Tonle Sap Basin seems unclear, according to scientist and conservation NGOs who fear that planned hydropower projects on the Mekong River will block migration routes and affect water quality.
Climate changes could also seriously impact fisheries, they say. A World Fish Center study on climate change and fisheries in Cambodia released last month indicates that the trey riel species is considered unstable under climate change because “their abundance is largely driven by the annual flood pattern, as they grow quickly and die young.”
“This emerging boom-and-bust cycle may be amplified by the higher hydrological variability predicted with climate change […] with years of abundance followed by years of shortage,” the report states.
The most immediate threat to fish in Cambodia’s great lakes and rivers is rampant illegal fishing which seems, however, to have diminished for the time being. Keo Ratha, who fishes on the Tonle Sap lake, said that the catch on the lake at the end of December had been better than previous years and that she was netting around 40 kilograms of trey riel per day.
“This year there is more fish than last year because the authorities cracked down on illegal fishing,” she said. “If they tighten the crackdown, there will be lots of fish in the Tonle Sap.”