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  1. #1
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    Default Would it be possible to grow pearls in saltwater mussels?

    We have a large green-lipped mussel industry in New Zealand. These mussels have iridescent inner shells, but I have never heard of them producing pearls and nor have I been able to find any research on this subject. I am wondering whether it might be possible to grow pearls in these bivalves or whether there would be some reason that this would not work?

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  2. #2
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    It's possible but mytiloida (mussels) present with unique problems separate from pterioda (pearl oysters) or even freshwater unionoda (freshwater mussels).

    What's your background? Any experience in aquatic biology or marine engineering?

  3. #3
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    No, I don't have the experience to do this - I am just curious. If it was possible, I'd love to see someone try it...

    What sort of unique problems do they have? They seem to have plenty of mantle tissue, but I'm not sure I could identify the gonad if trying to nucleate. I've never heard of them producing natural pearls either.

  4. #4
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    Quote Originally Posted by lizard View Post
    What sort of unique problems do they have? They seem to have plenty of mantle tissue, but I'm not sure I could identify the gonad if trying to nucleate. I've never heard of them producing natural pearls either.
    For a start, it's important to know a broadly used term "in the gonad" is not a good physiological explanation. Any damage, incision or disease of the gonad would almost certainly be fatal. In the pockets of connective tissues surrounding the gonads is a better descriptor.

    Mussels and pearl oysters have markedly different anatomies. In oysters the gonads are readily identified as a single organ, but mussels it's not. Instead they have a series of gonoducts that occupy the same space as the mantle. In nature, as the outer mantle develops, the reproductive ducts eventually infiltrate the mantle between the inner and outer epithelia. It's along this outer margin where donor tissue is selected and freshwater pearls are grafted in the recipient.

    Although the term freshwater oyster is commonly used, they're actually mussels. Marine mussels tend to be "spawny", for lack of a better term. They'll produce and release gametes almost any time of year, except during quiescence or the dead of winter. The spawning periods of freshwater mussels and marine oysters are much shorter. Even then, many pearl operations will induce spawning by relaying and sinking below thermoclines or other forms of deprivation (namely food) for short periods. In marine mussels, even after induction there will always remain undeveloped gametes, therefore the window of opportunity for grafting is very narrow. Any single unanticipated factor can cause the loss of an entire year's production.

    The same applies to the hearts. In mussels the heart is in pairs along each half of the hinge, but not a singular organ similar to oysters, instead a ladder like structure described as the pericardium. As such, mussels are indeed prolific producers of natural pearls, in far greater incidence than most mollusks, but because the spaces are smaller, the pearls tend to be smaller.

  5. #5
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    Thanks Dave - that is really interesting. I have seen pictures of pearls from Mytilus edulis, which might be similar to what might potentially be obtained from Perna canaliculus? I haven't found any references to pearls occurring naturally in our Perna canaliculus though.
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    Quote Originally Posted by lizard View Post
    Thanks Dave - that is really interesting. I have seen pictures of pearls from Mytilus edulis, which might be similar to what might potentially be obtained from Perna canaliculus? I haven't found any references to pearls occurring naturally in our Perna canaliculus though.
    Although perna and mytilus are synonyms, I looked at the taxonomy key and noticed different authors of the parent classification. Linnaeus classified Blue mussels in 1758, Gmelin classified Green mussels in 1791 and Conrad classified California mussels in 1837.

    I've added California mussels because it's my target species for pearl culture, climate change and biomedical research. Over the years, I've discovered numerous pearls in M. californianus with no visible nuclei present. The theory postulated the presence and behavior of histocompatibility antigens. Without getting overly technical, these are any antigen on the surface of tissue or blood cells that provokes an immune response and subsequent rejection when transplanted to an individual of a different antigenic type, thus determining whether the tissues or organs of a donor and recipient are histocompatible. In simple terms, the differences between antigens are inherited and determine organ transplant rejection.

    Now here's where it gets interesting. In reviewing these and subsequent authors, one major difference stood out. Green mussels are highly anti-inflammatory.

    Green-lipped mussel (Perna canaliliculus)

    Origin: Extract from a New Zealand mussel

    What we know: Mussels are rich in omega-3 fatty acids, and by reducing production of leukotrienes (inflammatory molecules) and prostaglandins, may have the same anti-inflammatory effects as fish oil.

    Studies: Results of both human and animal studies have been mixed. A 2006 Clinical Rheumatology review found benefit for both osteoarthritis (OA) and rheumatoid arthritis in two of five clinical trials. A 2008 review of trials for OA found benefit when green-lipped mussels were added to conventional therapies. Unlike NSAIDs, which can harm the stomach, green-lipped mussel extract may help heal ulcers.

    Dosage: Capsules, extract: 300-350 mg three times daily of extract for RA; 900-1200 mg daily for OA.
    And other research here.

    Therefore, it stands to reason natural pearls in Green mussels are less likely to occur by systemic disorders. That's not to say they won't generate pearls by physical anomalies. (ie) cracked or broken shells, boring parasites etc. though. If anything, experimental grafting of Green mussels may have a higher success rate due to a greater ability to tolerate homogeneic (same species) tissue. Grafting is a cultural event. It never happens in nature. While autoimmunity is a known factor, the greater part of natural pearls are xenogeneic (different species) or a combination of both in onset.

    It's worth a try, but trust me... it's no small task, even at a rudimentary level.
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    So if I wear pearls every day I can stop taking fish oil capsules?

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    Hahahaha Wendy!!!
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    Thanks Dave - I am learning a lot. Have pearls been cultured in Californian mussels or are they limited to natural pearls?

    Is there any difference in pearl growth between male and female marine mussels? Most of the photos I have seen so far look to have been of female mussels with pearls.

    From what I could find, pearling in blue mussels may be linked largely to parasites - and treated as a negative from a food-crop perspective? That ties in with what you say about immune response and potential anti-inflammatory differences in the green-lipped mussel. However, it might mean the lack of pearls could also be environmental - in one article I read, marine ducks seemed to play a part in the parasitic cycle, so the parasites might not be the same without the same birds? We have blue mussels here also, but not commercially farmed (although often grow at the top of the green-lipped mussel farm lines). Not sure if we get any pearls in them either - I will have a search around.

  10. #10
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    I have successfully grafted pearls in California mussels, though viability remains an issue. Mussels may change sex more than once in their life cycle, but not always. There also tends to be a predominance of males to assure motile fertilization of female fecundity. I have not observed any discernible differences in either natural or cultural incidences.

    It's true the greater incidence of pearls in mussels is relative to parasites. Parasites certainly don't discriminate sexes either. It's also true many parasites are due to birds or other fishes, but those tend to affect mussels in other ways. Digestive tracts, organs, gills etc. Most however are water borne, mainly annelids, pea crabs, protozoa or copepods... to name a few. Many of these emerge (post-metamorphic) from sediments to bore through shells or physically attach to soft tissues while the animal feeds. Most mollusks tolerate modest infestations and do not necessarily infect those that ingest them. Blue mussels more than others though, hence predominate competition at the tops of lines and the upper margins of the water column nearest the surface. Most mussels do not thrive embedded in sediments very well. On the other hand, mussels tolerate temperature shocks in far broader ranges than most creatures, especially in the intertidal zone.

    As such, line suspended mussels have a low incidence of natural pearls. Other dynamic forces such as wave action, rolling stones, logs etc. may cause shell damage, which create points of entry for parasites. Returning to the same reefs over the years, it's evident patterns emerge that natural pearls tend to occur in patches, nearest the substrate, namely sandy outcroppings. In niches, if you will. This stands to reason, as many predators behave in the same manner.

    If I were to survey blue mussels for pearls in your area, that's where I'd focus. You'd also do well to observe anomalies, aberrations, shell damage, worm holes etc. I'd also advice finding alternative uses for the shells, tissues and the data gleaned while using great discretion to ensure, possibly even enhance the biomass rather than reckless abandon. I have a policy of voluntary compliance, where I only gather amounts equal to permitted daily limits among recreational users.

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    Thanks Dave - I really appreciate the time you have spent replying to me.

    The study I saw mentioned trematodes as a pearling-inducer, with a life cycle that incorporated cockles as a primary host, then moving to blue mussels, with marine ducks as a third intermediary. We definitely have pea crabs in both types of mussel here. I'm not so sure about other types of parasites.

    I do like the photos of your californian mussel pearls. Maybe it is just the photos, but they seem to have better lustre and iridescence than the blue mussel pearls.

  12. #12
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    Quote Originally Posted by lizard View Post
    I do like the photos of your californian mussel pearls. Maybe it is just the photos, but they seem to have better lustre and iridescence than the blue mussel pearls.
    M. californianus are a much bigger shell. 30cm and more than a kilogram is not uncommon. The pearls are highly translucent and present with wonderful effervescent patterns. More than M. edulis or M. galloprovincialis, which tend to have high ratios of calcite throughout the life cycle. Californias get calcitic too, but at a much lower rate and usually from over-maturity.

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