Japanese Akoya Mortality


Nov 28, 2005
Hi Everyone,

I am surprised (or maybe I've just missed it), that there is no recent mention of the huge issue of the deaths of juvenile Akoya oysters here on the guide.
Is anyone following this matter and is there any recent news on this important issue that threatens to wreak havoc with the Akoya pearl trade?

I for one, sincerely hope that it can be brought under control and the cause dealt with as soon as possible.
Hi teeuk

I have not really heard of this happening at the moment...but in Japan's Akoya pearl farming -from my perspective- we don't have to wonder WHY are these mortalities happening; the question should rather be oriented towards WHEN will the next mortality occur???
And there are many, many reasons as to these mortalities continue to happen.

Thanks for your response.
I'd heard from a couple of sources that this started to be reported around September 2019, but perhaps because of the Pandemic appearing not long after, the news of this has not spread as much as it would have done in "normal" times.

Basically, it seems there were very big losses in the number of juvenile spat and no one seems to know the cause for sure.Some put it down to a new virus (somewhat ironically), while others believe climate change to be the cause.
The results of this will obviously soon come home to roost with production yields likely to be hit hard in the near future am very sorry to say.

There are a few references to it on the web, one of which is this: https://thesouthseapearl.com/blogs/n...xplicably-died

I came here looking for more up to date, information and was very surprised not to find any reference to it.

I truly hope that this situation is rectified very soon!
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When I was working on an akoya farm in Vietnam a couple of years ago mortality rates were a growing concern and the cause was that the sea was simply too hot. Oysters have a very narrow envelope for survival. they do not adapt. They just die.
The cure will be either finding a way to breed more temperature tolerant oysters of the same species, move the farms to cooler waters or move the farm ranks to cooler/deeper waters.
I am no expert on this, but this topic does remind me of the abnormal extreme weather caused by climate change in many places all over the world during the past year(s?). There are hot places that suddenly got very cold, cool places that got extremely hot unexpectedly, and not-wet places that rained heavily and continuously and flooded. Not sure if this happened to Japan but climate change is my main guess...
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I will quote some text from the article:

"As for possible factors for the mass fatalities, a Mie prefectural government study in September cited higher than usual seawater temperatures during the first months of this year, as well as a paucity of plankton that shellfish feed on.
However, prefectural officials have yet to reach a definitive conclusion. Such factors “may have contributed to the widespread deaths, but they are not the true cause,” a prefectural official said.
Scientists at the National Research Institute of Aquaculture in Minami-Ise, Mie Prefecture, suspected a possible infection of a transmitted disease among the shellfish, but none has been confirmed."

And this is the same story we have heard back in the 2010's, 1990's, 1980's...it is the same story, and the same explanation every time and I believe it is a case of the ostrich placing its head in a hole. The reality is that this is multi factorial problem, there are many "bunions" to step on and there are economic realities as well (policies and politics) at stake, smother with some pollution problems (fish farms produce a lot of waste!), the fact that the bays are not that open and there is little recirculation, add some increased temperatures (bacteria will flourish and consume Oxygen) and voila! You have another unexplained disaster!

In reality: Japan's Akoya pearl farming industry must change quite a bit to ensure its survival, but it must make a "reality check" and then elaborate strategies that will lead them into a true revival. In the meantime: we will listen about these massive mortalities every so many years.
I was asked on Pricescope pearl forum if the virus is causing problems this year.

I took that to mean: Is the virus is killing oysters this year? (Of course the mass mortality of akoyas a few years ago is causing ongoing problems in akoya pearl availability.)

Does anyone know the answer?
Yes, they are still dealing with pearl oyster mortality, which means low production for at least the next two years. Production is at about half of normal currently.

The auctions are going on right now and a friend of mine sent me the attached article. Auction prices are up another 40% in 2024, and sizes 5-7 are up more than 50% (7 mm includes 7-8 mm pearls).

This means within the last two years there has been a 3.75% increase in harvest auction prices:
2022 - 140%,
2023 - 180-200%
2024 - 140%.

He also said pearls are selling so well, both Mikimoto and Tasaki are out of strands and only allowing purchase of one item per customer at their retail shops.

34047 (1).jpg

Mass mortality of pearl oyster ( Pinctada fucata (Gould)) in Japan in 2019 and 2020 is caused by an unidentified infectious agent​

Tomomasa Matsuyama 1 , Satoshi Miwa 1 , Tohru Mekata 1 , Yuta Matsuura 1 , Tomokazu Takano 1 , Chihaya Nakayasu 1

Free PMC article


Mass mortality of 0-year-old pearl oysters, Pinctada fucata (Gould), and anomalies in adults were observed in Japan's major pearl farming areas in the summer of 2019 and 2020. Although adult oyster mortality was low, both adult and juvenile oysters underwent atrophy of the soft body, detachment of the mantle from nacre (the shiny inner surface of the valves), deposition of brownish material on the nacre, and loss of nacre luster. Infection trials were conducted to verify the involvement of pathogens in this phenomenon. Healthy adult pearl oysters were obtained from areas where this disease had not occurred to use as the recipients. The sources of infection were either affected adult oysters with atrophied soft bodies or batches of juveniles in which mortality had reached conspicuous levels. Transmission of the disease to the healthy oysters were tested either by cohabitation with affected oysters or by injections of the hemolymph of affected animals. The injection infection test examined the effects of filtration and chloroform exposure on the pathogen. Occurrence of the disease was confirmed by the appearance of brown deposits on the nacre and loss of nacre luster. The abnormalities of nacre were clearly reproduced in recipient shells in three out of four cohabitation trials with affected oysters. The disease was also reproduced in six out of six injection trails either with hemolymph filtered through 100 nm filter or with hemolymph treated with chloroform. In a serial passage with hemolymph injections, the disease was successfully transmitted through eight passages. These results suggest that the etiology of the disease is a non-enveloped virus with a diameter ≤100 nm.


Other mass mortalities of pearl oysters.

From 1969–1970 a mass mortality of pearl oysters occurred in pearl farms from Port Moresby (Papua New Guinea) to Kuri Bay and Smith’s Harbour (Australia). It was observed that death rate on many occasions reached 100 per cent and many times, out of one cage containing ten oysters, only one had survived (George 1992). Mortality of pearl oyster, Pinctada maxima was about 80 per cent, although 30 to 60 per cent was
more common in the Australian pearl culture industry since 1974. It continued for more than one decade, and a three-year investigation (1980–1983) into the causes of mortality was conducted. The investigation found that mortality was related to transporting oysters from fishing grounds to lease sites, which took a ship about 37 hours. During the longer fishing periods, collected oysters were held on board for a maximum of four or five days. The oysters were kept and transported in high densities on fishing vessels with inadequate water circulation, which caused a build-up of bacteria in oyster carrier tanks. A bacterium, Vibrio harveyi, was found to be responsible for high mortality rates in the tanks (Dybdahl and Pass 1985)


While the latter describes bacterial infection in history, the former suggests viral infection in Pinctada fucata. That can be worrisome. While bacteria can wreck havoc on a biomass, it's often short lived whether seasonally active or running it's course naturally.

In recent years, the west coast of N. America was infected by a syndrome known as "Sea Star Wasting Disease". This virus was first isolated and identified in 1948, but overall concentrations remained low. However, this has proliferated in the last decade, likely due to changes in marine pH (ocean acidification) and rising water temperatures though climate change. Densoviruses are small (18–25 nanometers in diameter) and non enveloped. Densoviruses are known to infect members of insect orders while some viruses infect and multiply in crustaceans such as crabs and shrimp, or sea stars from phylum Echinodermata. Densovirinae are a subfamily of Parvoridae, aka Canine/Porcine Parvovirus. I suspect freshwater mussels are highly resistant to this (especially China, where pig manure fertilizes those ponds) whereas marine mollusks are greatly more susceptible.

Over the years, farmers reduced densities especially during relaying and transportation and final grow out. Running a clean operation, allowing fallow 33% of the time and greater sterility during grafting procedures will greatly reduce mass infection bacteria (namely vibrio sp.).

Viruses on the other hand are not so concerned with environmental stresses whilst infecting oysters. The infection rate among populations are very high, where mortalities follow. 80% is an insidious rate. Like fish, once a rate of 50% is surpassed, the better proactive solution is 100% destruction, lest surviving brood stock become infected. "Whirling Disease" in salmonids and trout is caused by a protozoan parasite carried by snails in fresh water streams, thus the entire biomass must be anhilated and otherwise reintroduced. That's not practical for marine mollusks though, because the virus is still present in the water column.

For years, relaying shellfish was commonplace. Once harvested, fishermen tended to relay to temporary locations pending sale. Producers very often relayed contaminated stocks to clean areas to flush toxins then sell them later. During my time contracting samples for red tide testing, we were required to relay mussels from clean areas to contaminated areas for 30 days then send them to the lab. Thus uptake is controlled as far a human biotoxins are concerned, but may give rise to spreading viruses to susceptible biomasses.

Although DFO approved (even insisted) relaying in my operation, I saw it as problematic. In 2011, oyster farms near Lagoon Island were infected with Norovirus (Macrocytosis mykena). I voluntarily suspended relaying from the farm for fear of infecting other areas. Instead, worked "in situ" with wild stocks. At the end of the day it was a lot less work, but not without other issues. While norovirus is not particularily harmful to shellfish, it poses a serious health risk to those who consume it.

Relaying invariably leads to monoculture, a dirty word to mother nature. Healthy populations come from genetic diverisity, not inbreeding or overcrowding. In our history as a society, monoculture provides sustainance for a massive population, where scarcely a farm exists where innoculation/sacrifices due to viruses are not standard operating practices.

Fishermen and farmers are generally marginal interests economically. Simply put, there are not enough resources to undertake even the simplest scientific research, no less something complicated as virology. Wholesalers, manufacturers and retailers generate millions, probably billions over the years, do woefully little for science and research. Japan and Australia to some degree, but mostly taxpayer funded because their respective countries depend on it. A grant here or a bursary there is all well and good locally for job creation, training or community support, but in the big picture, pearl farmers are left to their own devices for survival.
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