The Effect Of Donor Hyriopsis Cumingii On The Quality Of Pearls

Hyriopsis cumingii is the main freshwater pearl mussel in China, which producesover85%pearls of the world. Researching on how donor and host mussels affect thequality of pearls is important to make breeding scheme and improve the quality ofpearls. In this paper, how donor and host H. cumingii affect pearls’quality was analyzedquantitatively. And on the basis of the donors’ contribution to pearls’ quality, a newtechnique to obtain mantle pieces from donor mussels with keeping the donors alivewas exploited, and then healing and regeneration process of donors after donatingmantle pieces was histologically observed. The molecular evidence of donor musselsaffecting pearls’ quality was discovered. This study provides reference of selectivebreeding of donors and hosts which aim to enhance the quality of freshwater pearls.1. The effect of host and donor H. cumingii on the quality of pearls.Before grafting the saibos into mantles, the growth traits and specific growth rate(SGR) of100donor mussels and100host mussels were respectively measured. Atth18th month after grafting, the sizes, weights, circularities and colour parameters of1746pearls mussels produced were measured. The SGR (shell length), SGR (shellheight), SGR (shell thickness) and SGR (weight) of the hosts had highly significantly(P<0.01) positive correlation with pearls’ weights and sizes, with the degree ofcorrelation: SGR (weight)> SGR (shell thickness)> SGR (shell length)> SGR (shellheight), and had no significant correlation with the circularities and colour parametersa*, b*and C*of pearls. The SGR (weight) of the hosts had a highly significantlypositive correlation with the pearls’ lightness L, and a highly significantly negativecorrelation with the pearls’ colour difference△E. The weights and sizes of the pearlshighly significantly positively correlated with the shell height and shell length of thedonors, and the circularities of the pearls had highly significantly positive correlationswith shell lengths, shell thicknesses and body weights of the donors, with the degree ofcorrelation: shell thickness>body weight>shell length. The colour parameters of thepearls had no significant correlation with growth rates of the donors. Weights, sizes andcolour parameters of the pearls had no significant correlation with colour parameters L*、a*、b*、C*and△E of inner shells of the hosts, and circularities of the pearls had nosignificant correlations with colour parameters of inner shell of both donors and hosts.Weights and sizes of the pearls had highly significantly positive correlation with L*ofthe donors’ inner shells. Colours of the inner shell of donors had relatively great effecton colour of the pearls, among which L*of the pearls had highly significantly positivecorrelations with L*of inner shells of the donors, and highly significantly negativecorrelations with a*、C*and△E of inner shells of the donors. a*of the pearls hadhighly significantly positive correlations with a*、b*、C*and△E of donors’inner shells.The b*and C*of the pearls had highly significantly positive correlations with b*andC*of the donors’ inner shell, and had significantly (p<0.05) positive correlation withthem. The△E of the pearls had highly significantly negative correlations with L*of thedonors’ inner shells, and highly significantly positive correlation of a*、C*and△E ofthem. There was no significant difference between the pearls’ weights, sizes,circularities and L*produced by mantles from anterior and posterior location of thedonors, and there was highly significant difference of a*、b*、C*and△E between them.Average value of a*and b*of pearls from posterior locations were highly significantlyhigher, and saturation C*and colour differences△E of pearls from anterior locationwere highly significantly higher than that from posterior locations, which indicated thatcolour of pearls from posterior mantle of the donors were deeper and more gorgeous,whereas the pearls from anterior locations were whiter. This study provided reference ofselective breeding of donors and hosts which aim to enhance the quality of freshwaterpearls.2. Healing and regeneration of donor H. cumingii after donating mantle saibosAfter excision of mantle tissue from H. cumingii, survival rates, specific growthrate, healing and regeneration were observed and quantified for three months. Highsurvival rates (94.7%,92%,95.3%and94.7%, respectively) of mussels with small (8～12mm×8～12mm)(S-group) excision taken from the front, middle and back of theventral mantle margin, and control mussels were observed, and no significant differencewas observed among the four groups. The specific growth rates, SGR (length), SGR(thickness) and SGR (weight) of H. cumingii with different excision locations did notdiffer significantly but the SGR (height) of the group with the front excision was significantly lower than that of the other excised groups and controls. Mussels wereexcised with small, medium (8～12mm×28～32mm)(M-group) or large (8～12mm×48～52mm)(L-group) from the middle ventral mantle margin. The survival rates ofmussels with S-, M-and L-group and controls were, respectively,92%,90%,90.7%and94.7%. The survival rate of the L-group was significantly lower than that of the otherthree groups. The trends in SGR (length), SGR (height), SGR (thickness) and SGR(weight) among the four groups were similar: controls> S-group> M-group>L-group.Macroscopic observation of mantle tissue showed that the wound area became reducedsince12thd after the excision. To grow to the same level as the surrounding normaltissue, the regenerated tissue needed40d,75d and90d, respectively, in the S-, M-, andL-group. Histological observation of wound tissues showed that haemocytes aggregatedat the wound site soon after excision and completely sealed the wound after12h.Epithelialization sealed the wound completely after72h. The three mantle lobes beganto form at15d. The regenerated lobes were morphologically different from normaltissues after25d but were identical to the normal mantle lobes, in both morphologicalstructure and function, by90d. This is the first report on the survival rate, growth rate,wound healing, and regeneration in the freshwater pearl mussel after excision of itsmantle tissue. The study demonstrates that donor mussels, without being killed, maydonate mantle pieces (saibos) for evaluating the effect of donor mussel on pearl quality.Donor mussels contributing to pearl quality, this provides support for selective breedingof donor mussels in the future.3. Molecular evidence of donor H. cumingii affecting quality of pearlsMantle pieces of Anodonta woodiana were grafted into mantle of H. cumingii,which were subsequently cultured for10months. With the polymorphism between thenucleotide sequence of ITS-1of H. cumingii and A. woodiana, specific primers weredevised. ITS-1sequence amplified in genomic DNAof the pearl sacs matched that of A.woodiana in Genebank with517max score,99%query coverage,3e-143E value and99%max ident, and the similarity of PCR products between the pearl sac and A.woodiana amounted to99%. This implied that after10-month culturing, H. cumingiihad accepted mantle pieces of A. woodian, and the cells of A. woodiana still existed.With formation of pearls, donor cells did not die and dissolve, but continued proliferating. This study provides the evidence of donor cells’ persistence in pearl sacsduring nonnucleated freshwater formation of pearls, offering basic material for selectivebreeding of H. cumingii.