Tuesday, April 21, 2009

Quick Lesson in Genetics


There is a lot of talk about the Triploid oyster in the Chesapeake Bay region especially in oyster aquaculture. I have heard some things over the last few years that I just want to try and clear up as well as just throw in my two cents...remember you get what you pay for.


WHAT IS A TRIPLOID?

First, what it is not...
A TRIPLOID IS NOT AN ASIAN OYSTER !!!!
This misunderstanding has troubled me the most and I've heard it frequently. The Asian oyster (Crassostrea ariakensis) was required to be studied in a triploidy form so it wouldn't reproduce so we wouldn't end up with a bay full of asian oysters by accident. But somehow the word triploid began to be synonymous with asian oyster...this is not the case... any oyster can be produced in a triploid form. Pretty much every triploid oyster being raised in Virginia today is a triploid C. virginica not C. ariakensis.


Now what it is...
Triploidy, is a form of polyploidy which means having more than two sets of chromosomes. Your average run of the mill organism has two chromosomes or is known as a diploid. You and I are diploid creatures, we have one chromosome from mom and one from dad. In the case of the triploid oyster there are three...tri = three. Polyploidy is a common occurence in nature especially in plants. However, our triploid oysters don't come to us naturally triploid that is something that is worked out in a lab...we talk about this later.



HOW DO YOU MAKE A TRIPLOID?
4n + 2n = 3n

Definitions...
4n - TETRAPLOID (4 chromosomes or way to many chromosomes for its own good)
2n - DIPLOID (2 chromosomes...standard issue)
3n - TRIPLOID (one extra set of chromosomes, so three total, so it is infertile or will not/should not reproduce)


WHY WOULD YOU WANT A TRIPLOID?
Two reasons...
1. Triploids "tend" to grow faster.
2. Triploids "tend" to have good meat content throughout the summer, because they don't become "poor" and that is because they don't spawn. So a triploid should have a meat yield in August similar to Febuary, so more market potential.


WHERE DO TRIPLOID OYSTERS COME FROM?
This is a little complicated.
ABC (Aquaculture Genetics and Breeding Technology Center) at VIMS (Virginia Institute of Marine Science) handles the breeding and production of disease resistant lines of oysters; DEBBIEs, CROS breeds, etc... they provide the "brood stock" to hatcheries who spawn them to produce your seed. You pay a royalty fee to VIMS for the use of those lines. However, the head of ABC is also one of the owners of a private company (4c's Breeding Technology Inc.) that has a patent on the triploidy process. You pay a seperate royalty fee for triploidy to the private company. You see this in the price of seed from a hatchery $6/1000 no royalties, $7/1000 disease resitance royalties, $8/1000 disease resitance and triploidy royalties. What occurs is that ABC produces the disease resistant brood stock and then someone at VIMS/4c's produces the tertaploid oysters through the patented process, so VIMS pays a fee to do that I think. Regardless, they produce tertaploids and supply hatcheries with living tetraploid oysters which can be conditioned and used for the production of triploid seed or they produce tetraploid oysters and get the sperm from those oysters and provide that to the hatcheries for the production of triploid oysters. Clear...muddy...check out 4c's website it spells out the whole process... http://www.4cshellfish.com/


HOW DO I GET TRIPLOID OYSTER SEED?
Ask for it when you place your order with any hatchery, then hurry up and wait...

and wait...

have your delivery date pass and wait...

now begin to sweat and wait...

sweat, wait, and hope some triploid seed comes in...

then do all of that again and start counting the number of weeks of growing time you are losing because you are waiting for that triploid oyster...

now you find out the reason you are waiting is because (anyone of the following have occured) the original tetraploid brood stock was mostly female, the brood stock wouldn't condition, the sperm was no good, the stuff mated but it looks "funky", all of which point back to the production of the tetraploids...

If your lucky some seed comes in, not all that you ordered. Then you hope that the seed that did come in is actually in top notch shape because the hatcheries were having a difficult time producing the triploids and that has to make you question the quality of the genetics...

So we end up short on triploid seed as an industry again and this leads to the VERY FALSE idea that our private hatcheries in Virginia can't handle the demand and that the state should step in and fill the void with its own hatchery, VERY BAD IDEA ...I wonder why they would be pushing for that so hard?

In the mean time you may want to consider looking for some diploid oyster seed. So you won't have the meat yields you might want for summer time (July, August) atleast you'll have some gorgeous oysters to sell a year from now when the market is hot. There is nothing worse than having a good market and running out of oysters because you just didn't have enough to start with, or they are just not big enough because you got them late.

A few of us in the industry have been toying with locally resistant strains of oysters over last several years. VIMS calls this "backyard breeding", we call it not paying a 15% royalty fee on 4 million oysters, its save about $8K. But more than that it has given us some solid gold oysters to work with outside of the triploid.


Final note...
We are not against the triploid C. virginica in any way, it is an awesome oyster when all things come together, what we struggle with are the constant issues with the production of the triploid seed. It is inconsistent, to say the least, and a risky proposal to assume you will be able to get nothing but triploids on your farm. It is wise to always have some other strains of oysters on hand both diploid and triploid just because you never know what mother nature will throw your way.
These struggles in the industry are just growing pains, it is part of the process of becoming bigger than we are, which is a good thing.

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