Studies On Artificial Reproduction And Taxonomic Status Of The Pacific Geoduck Panopea Generosa

Pacific geoduck clams(Panopea generosa), are the world’s largest burrowing clamand a commercially important species in north-western North America. The burialdepth varies from0.6to1.0m, which determines by substrates. The Pacific geoduck’ssiphon is not only rich in highly unsaturated fatty acids, taurine, but also rich inpolysaccharides, which has antioxidative activities. However, as the implement ofIndividual Vessel Quota from North America and habitat destruction, the populationsof pacific geoduck clams are declining. The tidal flats of Shandong and Liaoningprovinces cover an vast area, which is probably suitable for pacific geoduck’s growthand reproduction. Thus, it is meaningful to establish the techniques of artificialreproduction of the pacific geoduck for the protection of natural resouces andinitiating aquaculture activities in this species.Molecular systematics enables not only the identification of species effectively, butalso the inference of phylogenetic relationships, which can make up for the defect ofspecies identification basing on mrophologecal characteristics. Pacific geoduck clamshave a confusing taxonomic history, such as synonymy and unclear speciesboundaries. DNA sequence information from fragments of two mitochondrial genes(COI and16S rRNA) were used to confirm the taxonomic status of the Pacificgeoduck clams and the relationship with its related species.Artificial breeding techniques of the Pacific geoduck, P. generosa, includingbroodstock culture, spawning induction, and larval rearing were investigated in thisstudy. The results showed that at salinity of28-30, the fertilized eggs reared at11℃,13℃and16℃developed to D-shaped larvae after83h,60h and46h, respectively.At the temperature of16-18℃, the D-shaped larvae developed to the stage ofmetamorphosis in about20days as the shell length increased to380μm, which wascharacterized by the appearance of foot and siphon. After rearing of about70d, theshell length of juvenile P. generosa reached5mm. Growth rate of shell length of thelarvae at D-shaped and umbo stages was6.2μm/d and16.8μm/d, respectively.Aftermetamorphosis, the growth speed of shell length became faster. The settlement of the larvae in the experiments with four different substrata was compared and the resultsshowed that the highest setting rate was achieved for the attachment substance of finesand, followed by pebbles, nylonets, and plastic sheets.Partial sequences of mitochondrial COI gene from17specimens (62individuals)and16S rRNA gene from9specimens (47individuals) within the order Myoida wereanalyzed. Comparisons of within and between species levels of sequence divergenceshowed that the genetic distances, within and between species of COI sequences,ranged from0.000to0.001and from0.117to0.638, respectively, and that of16SrRNA sequences varied from0.000to0.005and from0.136to0.753, respectively.The genetic variation between species exceeds that within species either based on COIor16S rRNA gene, which indicates the DNA barcoding gap existing. TheNeighbor-joining (NJ) and Bayesian trees based on COI and16S rRNA genes showedthat all species fell into reciprocally monophyletic clades with high bootstrap values.The Hiatellidae formed a clade with Panopea and Hiatella, besides, the clade ofPanopea was composed of P.generosa, P. globosa, P. abbreviate, P. japonica and P.zelandica with high bootstrap values. The other clade included Mydiae, Corbulidae,Pholadidae and Teredinidae. We analyzed the nucleotide composition, NJ tree andBayesian tree of five clams within genus Panopea, the results showed that the P.generosa and P. globosa were two distinct species, the genetic relationship between P.generosa and P. japonica was closest.