Obtaining the “Seeds” for your Farm
In order to “fatten” or grow your pearl oysters from a “juvenile” stage, what many refer to as “seed” or “spat” (oysters measuring between 2 and 8 mm), you either buy your litle oysters from specialized bivalve producing lab-facility, or you must establish a “wild spat collection” program. “Lab-raised spat” can be a very good option, but it may have a few disadvantages that are solvable. Let us first consider the advantages and then the disadvantages of Laboratory produced Juveniles:
- You may have your spat at the desired schedule for your operation.
- You can have all the spat you need for your farm.
- Juveniles will have a very similar size (homogeneous) and growth rate.
- The “Lab” may not produce spat for you due to a lack of demand (important if you use native or endemic species).
- The quality of the spat may be very low (=high mortality and or lower growth).
- The spat may have low genetic variability, since they come from a small group of “parents”.
The advantages of obtaining “spat” from wild-collectors are many, but it also has its disadvantages:
- The seed is inexpensive (almost free!)
- The spat has undergone a “natural selection” process, where only the “stronger” (or “luckiest”) survived.
- There is much genetic variability within the group, which makes them less likely to die from some environmental change or a disease.
However, in regard to the disadvantages we have:
- You fully depend on the environment to capture your baby-pearl oysters, and it is becoming increasingly more difficult to predict the exact time for spat-collection (due to environmental changes) and
- It is almost impossible to predict the amount of seed that you are going to obtain and, in addition
- Your Juveniles will have variable sizes (heterogeneous) and you simply
- Do not know the group’s their “genetic make-up”: you could end up with “oyster-duds”.
Therefore, it is necessary to carry out, for months or even years, proper tests to find the most suitable areas for spat collection and understand in detail the reproductive behavior of the pearl oysters within the area of cultivation. Still, it’s easy to mess-up and obtain fewer than the desired amount of spat, so a mixed strategy can be more profitable: use both laboratory and wild–caught spat.
At our farm in Guaymas, we have been blessed with good seed collection areas that have allowed us to rely 100% on wild-caught spat since 1994, but we have experienced environmental disruptive phenomena (such as an “El Niño” or a “La Niña” Year) that have caused us major problems in this area. However, seed production laboratories in the region do not sell pearl oyster spat… due to a lack of customers.
So far we have only seen this strategy –the use of spat or “seed”- to start your pearl farm, but in a future post we’ll also discuss the other strategy: gathering large, wild-bred pearl oysters… but even before we compare all these strategies: how do you think these strategies can affect the environment? Surely the answer will surprise you (unless you already know something about this topic)…
What can happen if I use “Lab-Raised Spat”?
If this strategy is used properly, your farm can enjoy an uninterrupted supply of juvenile oysters, without ever having to depend on the environment’s natural supply. But, as with so many other things in which Humans get their hands-in, it can also lead to at a least pair of “unfourtunate” environmental problems. Among these we have “Genetic Pollution” and also the world-wide ocurrences of “massive pearl oyster mortalities”. Here’s why:
Setting: Japan, in the early 1960’s when the pearl aquaculture industry began a period of growth that seemed inexhaustible… thousands of pearl farms with their hundreds of rafts and thousands of culture cages, all inside the crowded bays of this island nation. With millions of “Akoya-gai” pearl oysters in culture there simply there were no more “wild-bred” pearl oysters available (most of these had been fished out to supply the pearl aquaculture industry) and there was not enough wild spat for the farmers. Since the Japanese people have been using research to advance their aquaculture technology, they generated enough knowledge to be able to rear laboratory-produced juveniles of all types of mollusks. Under this production system all that is needed is to procure a couple of oysters, an “Adam and Eve” if you will; from this couple you will be able to obtain millions of baby oysters (a female oyster can produce -depending on the species and other conditions- between 100,000 and 1 million eggs in a single “egg discharge”) or “spat”.
The problem that may be generated under this system is that all your oysters are descendants of this single pair of oysters (your “studs”), thus they are all siblings, and genetically speaking: these oysters are very similar (but not identical, remember that there is a genetic effect known as “Genetic Recombination” which makes it possible for an increase in genetic differences). This makes them more likely to react similarly to environmental change or disease: if one of them becomes sick… most likely all others will too. This problem can be avoided using a larger number of parent oysters or “studs” and we will gain a much greater genetic variability among our pearl oysters. Unfourtunately, once producers have used this productive system, they will imediately begin with the selection of “strains” or “Breeds” of genetically improved oyster stock, in which the parents are selected solely based on characteristics that are considered as desirable, such as:
- A faster growth rate
- Better Shell-Shape and/or
- Better Shell color (=color of the pearl)
And this is where a vicious cycle can begin, having no end in sight until its consequences become catastrophic, yet very few seem to care about this problem. Originally, pearl oysters are selected with the characteristics of faster growth rate and shell color, and from these you get a first generation (F1) of oysters that may be larger, grow better and produce pearls with a more similar color. Initially, this is something very good for the producer, since he’ll have the ability to introduce just the “right product” for the mass market: most pearls will be very similar and you can produce tens of thousands of identical pieces.
However, if the the farmer re-runs the selection of broodstock (from the F1 or first generation) he will be able to further refine these characteristics: the pearl oysters will grow even faster and will have a better color selection. And so, the process is repeated for several generations… until his organisms (let us say, in their F10) become “genetically depressed” in a process known as inbreeding.
I ask the question again: What does the Environment think of this? How can we affect the Environment? Well, let us gather some information from the Wikipedia on this topic:
Inbreeding is the reproduction from the mating of two genetically related parents, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is called inbreeding depression. Deleterious alleles causing inbreeding depression can subsequently be removed through culling, which is also known as genetic purging.
Thus, growers should avoid the phenomenon of “genetic depression” through a less stringent selection or by introducing “new blood” -originating from wild oysters- so as to avoid this negative phenomenon.
Negative Environmental Impact from using Lab-raised Spat
Although I would like to say that there is absolutely no negative impact, I must declare just the opposite. There is evidence that the use of lab-raised organisms can have an effect known as “genetic pollution” upon the wild-bred populations. This is something that is believed –by some- to have had affected the Japanese populations of Akoya-gai (Pinctada imbricata) oysters and could have helped cause the already known mass mortalities of pearl oysters. How so? Because of the production of sexually-infertile chromosome-altered oysters know as polyploids. These oysters are supposed to be infertile, thus the energy an oyster devotes to reproduction is instead spent on growth…a great thing for any pearl farmer, but as with all good ideas some are not that good. So, some of these unfertile polyploids began reproducing, their altereded gametes giving rise to some “Franken-Oysters” that settled in Japan’s bays, becoming part of the Akoya-gai’s “gene pool”.
But why do these things happen??? Because we cannot put a leash on Nature, because we just lack the Humility to accept that sometimes we just have a great tendency to wreck things up, and very specially when it comes to the environment.
This aspect is similar to the “Wild Corn vs GMO Corn” controversy: pearl oysters are key species in many ecosystems and they also have cultural-value in many lands, why not just take care of the critters and raise decent cultured pearls and doing it in the best possible way? Well, there is always someone who goes the extra-mile to get an extra penny…seems this is what Life is all about after all.
Our solution to this problem is simple: AVOID using inbred organisms, by always introducing “new blood” (wild-organisms from your locality to prevent any damage) into your selected “breed” and to always avoid using chromosomic-freaks. Mexico –among many others- is a Megadiverse country, and deserves the protection of its remaining natural resources: these belong not only to us, but to our children and all future generations, and as many have stated before: the Environment knows nothing about borders, languages or Human culture, so in essence it belongs to whole of Humanity and for all other Living beings with which we share this beautiful blue planet.
Let us learn from the mistakes of others, and avoid falling into the habit of continuously using “damage control” techiques. In the next post I will discuss the “collection of wild spat”. Until next time!