Mass die-offs at fish farms push up flounder prices as seas warm

"There was a time you could buy two fish for 10,000 won."

Flounder has long been the most accessible fish for raw-fish lovers in Korea. Farmed in large volumes year-round, it earned a reputation as the everyday sashimi choice — affordable regardless of the season.

But flounder prices have been rising sharply. Since 2020, wholesale prices have nearly doubled.

The culprit is a growing wave of mass die-offs at fish farms. Record seawater temperature increases, year after year, have driven up mortality rates at aquaculture operations across the country.

This year, which has brought another historic heat wave, is no exception. More than 100,000 fish died at farms in just the past week.

The deeper concern is that this summer may be the coolest one Korea sees for years to come — making further price increases for flounder and other farmed fish all but inevitable, analysts warn.

According to a heat wave response report released Tuesday by the Ministry of Interior and Safety's Central Disaster and Safety Countermeasures Headquarters, a total of 360,707 farmed fish had been reported dead from high water temperatures nationwide as of Monday. That is 5.1 times the figure recorded at the same point last year, when 70,917 fish were reported dead.

Flounder losses in the southern coast and Jeju regions have been particularly severe. According to South Jeolla Province and Wando-gun authorities, 115,800 flounder died at 10 fish farms in Wando-gun through Tuesday. On Jeju Island, more than 33,000 flounder and other fish were reported dead at six farms through last Thursday.

The die-offs stem from a rapid rise in sea surface temperatures accompanying this year's record heat wave. Flounder thrive in water between 18 and 24 degrees Celsius. Once temperatures exceed 25 degrees, their digestive function deteriorates and feed intake drops sharply. Near the survival threshold of around 29 degrees, organ failure and weakened immunity combine to raise the risk of mass death sharply.

Water temperatures near the southern coast and Jeju Island — where flounder farms are concentrated — have recently surged to nearly 30 degrees Celsius. High-water-temperature warning zones are issued when sea temperatures reach 28 degrees or above for three or more consecutive days. The number of such zones expanded rapidly within days: from six last Thursday to 17 on Monday.

Mass die-offs at fish farms are not a new phenomenon. As climate change intensifies summer heat waves, the damage has grown steadily worse. In 2024 — the hottest year on record — Korea's aquaculture industry suffered its largest losses ever.

Total damage to farmed aquatic products that year reached 143 billion won ($100 million), a record high. On Jeju Island alone, about 2.215 million flounder died at 78 land-based farms, causing more than 5.3 billion won in losses. Last year, about 1.8 million flounder died at 62 farms on Jeju.

The damage does not stop at the farms. Reduced supply feeds directly into higher prices. Since the 2020s, when average temperatures began rising more noticeably, flounder prices have climbed steadily.

Data from the Korea Maritime Institute's Fisheries Outlook Center show that the average annual wholesale price of flounder rose 72 percent, from 11,025 won per kilogram in 2019 to 18,989 won last year. The price increase felt by consumers is likely even steeper: as raw material costs rise, margins at each stage of the retail supply chain also expand, pushing up other costs along the way.

Significant losses are expected to continue through the rest of this summer. The sea was unusually warm even before summer began. The National Institute of Fisheries Science analyzed satellite observation data and found that the average sea surface temperature in Korean waters from January through June this year was 17.17 degrees Celsius — the highest since such measurements began.

The long-term outlook is grimmer still. A systematic ocean survey by the National Institute of Fisheries Science found that the average annual sea surface temperature in Korean waters rose a total of 1.60 degrees Celsius between 1968 and 2025, at a rate of 0.0276 degrees per year — more than double the global average increase of 0.76 degrees over the same period. In the past decade alone, the rate of warming in Korean waters accelerated to 0.09 degrees per year, three times the 35-year average since 1991.

The heat wave's toll extends beyond marine life. Livestock deaths from this summer's heat wave — including chickens, ducks and pigs — have reached 551,215 animals. With farmed fish and livestock suffering losses at the same time, concerns are growing about so-called "heatflation," in which extreme heat drives up food prices.

A Bank of Korea report on the impact of climate change on domestic inflation found that if monthly average temperatures remain 1 degree Celsius above the long-term monthly average — based on data from 1973 to 2023 — for a full year, agricultural product prices would rise 2 percent. The overall consumer price index would increase by 0.7 percent as a result, the report projected.

Meanwhile, the Ministry of Oceans and Fisheries raised its high-water-temperature disaster alert to "Serious Level I" last Thursday. The ministry and local governments are encouraging fish farms to bring forward harvests and carry out emergency releases, while operating high-water-temperature response equipment and expanding on-site inspections to guide farm operators on adjusting stocking density and suspending feed supply.

Oceans and Fisheries Minister Hwang Jong-woo attended a situation review meeting of the high-water-temperature emergency response headquarters that day. "Damage from high water temperatures not only threatens the livelihoods of fishermen but also affects food prices for the public," he said, calling on the government, local authorities and related agencies to work closely together. "Please make every effort, centered on the field, to prevent losses."