The Smoke and Mirrors of the R Rule

Stu Meltzer
May 17, 2020
August 9, 2017

The 'R' Rule

Everyone in the seafood business should be familiar with this concept, the age old guideline to only eat oysters in months that contain the letter R.  Most of us are aware that this recommendation exists because bacteria that can be harmful to humans (such as vibrio) has the greater likelihood to flourish under warmer weather (and water) conditions.  Today, oyster growers have the necessary equipment and technology to bring the temperature of harvested product down quickly to inhibit any bacteria growth. Further, supply chain partners (such as yourselves) maintain rigorous processes to keep oysters at the appropriate temperatures to mitigate incidence of bacteria growth.  In sum, harmful bacteria as a reason to avoid oysters in warmer months no longer applies.

The other motivation for this concept is the fact that oysters spawn during the summer months.  The graph below illustrates the shell volume for oysters over the course of a year.  You will notice that oysters begin to feed and put on weight starting in January. During early spring, the oysters begin eating more and developing egg and sperm in advance of their spawn.  This explains the uptick in weight in early spring represented on the graph.  After the spawn, the shell volume plummets, creating a less than desirable eating experience. In the fall, the oysters start putting on weight again to carry them through the winter. 

Cassostrea virginica Shell Volume/Density

Although people, particularly on the East Coast, associate summer and the beach with oysters, you can see that summer may be the worst time to be eating them from a product quality perspective. To remedy this situation, some smart and determined oyster loving scientists figured out how to develop an oyster that does not spawn, known as a triploid.


Like humans, oysters are naturally diploid organisms.  This means that oysters have two sets of chromosomes.  Triploids are organisms with three sets of chromosomes. This uneven number of chromosomes mostly renders these organisms infertile.  As you could gather from the previous discussion, an oyster that does not reproduce would theoretically maintain their quality during the time of greatest market demand. 

This is the advantage of the Triploid oyster. That said, the adoption of Triploid oysters by growers is not as widespread as you might expect.  Triploid oyster seed can be a bit more expensive than their diploid counterparts and, depending on what climate the grower is in, spawning may have a marginal impact on product quality, but for the regions where spawning can greatly impact product quality, triploids can be an undeniable asset.    

As you can see above, the triploid oyster is plump and ready for slurping, even in the warmest months, but it may be as good as it gets throughout the season. The diploid oyster shown just after spawn is still edible, but there is not much to the meat and the flavor falls flat. Fast forward a few weeks, and this oyster will take on a whole new personality with a dynamic brine and texture that is worlds apart from the picture presented.

In Summary

Natural oyster physiology should still be considered when choosing when to promote oysters. Early spring can be a good time, but if that is timed incorrectly, your customers can end up with spawny oysters.  We strongly recommend you run oyster promotions in the fall.  The oysters are fattest and supply is greatest. Sadly, summer will be over before we know it.  Let’s start talking about running a fall oyster special with you now!  

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