Studies On Mass Selection And Gill Microstructure Of Pinctada Fucata

In this study, path analysis of morphological characters of cultured pearl oysterPinctada fucata stocks from Sanya, Beihai and Xuwen was conducted. The multipleregression equation for body weight was established. Based on the three cultured stocks,I established nine complete diallel crosses. Subsequently, the growth performances ofthe F1crosses, hybrid vigors and general and specific combining abilities of the sixcrossbreds were investigated. The histological structure of the gill tissue in P. fucata wasalso studied by using light and electronic microscopies for the first time. The results areas following:1. The correlationship and path analyses of growth-related traits of pearl oyster PinctadafucataThe effect of various traits in Pinctada fucata from different populations upon bodyweight was examined. The correlation coefficients among the traits were calculated, andthen path analysis was conducted by taking the body weight as a dependent variable, andother six morphometrics as independent variables. The results show that correlationsamong traits of Sanya populations are significantly different （P<0.01） except the onesbetween ligament width and the other variables. The biggest is the one between shelllength and body weight （0.9228）. The path coefficient between shell length （X1） andbody weight （Y） is0.5083, suggesting that X₁is a major factor among others and has thestrongest direct effect on body weight based on path analysis. The shell height and shellwidth have smaller direct effect on body weight based on path analysis （P₂=0.1900,P3=0.2176） and show significantly indirect effect on body weight through shell length（P2=0.4664, P₃=0.4297）. It can be concluded from the result of high correlation index（R2=0.8977） that the path coefficient analysis can reveal the true relationship betweenthe independent variables and the dependent variables. The multiple regression equationobtained to estimate body weight based on shell morphometrics is: Y=-43.2267+0.6873X₁+0.3182X₂+0.9379X₃. The results for the Beihai and Xuwen populations are a little different from those of Sanya population, but the order of three shell traits’determination effects on body weight is the same as that in Sanya stock. This provides ascientific base for selecting traits for measurement in selective breeding programme ofpearl oyster Pinctada fucata.2. The construction and the growth performances comparison of diallel crosses from threecultured Pinctada fucata populationsComplete diallel crosses within and among geographically different populations, i.e.Beihai（B）, Xuwen（X）, and Sanya（S）, of P. fucata were made in order to breed newstrains for genetic improvement. Nine F₁populations have been obtained, includingthree purebreds, BBF₁, XXF₁and SSF₁, and six crossbreds, BXF₁, XBF₁, BSF₁, SBF₁,XSF₁and SXF₁. Subsequently, their growth performances at different months werestudied. The results show that SBF₁and SXF₁were more excellent than other ones in thegrowth performances as a whole. So they can be considered as the materials for furtherselective breeding for rapid growth variety. At the same months, the variation of shellwidth was not significant. But with the growth of P. fucata, shell width for each crossincreases gradually.3. Genetic analysis on complete diallel crosses of Pinctada fucata based on three culturedpopulationsFor the nine complete diallel crosses as established above, hybrid vigors, generaland specific combining abilities were analyzed based on four growth traits data at theage of8months. Genral combining abilities in shell length, shell height, shell width andbody weight for Sanya stock were3.60,4.24,0.96and1.92, respectively, while specificcombining abilities in shell length, shell height, shell width and body weight for S×Xcross are1.46,1.82,1.25and2.56, respectively. The results show that heteroses in thefour growth traits were found ranging from0.24%to52.62%in crossbreds. Heteroseswere different for different combinations and different traits. The heteroses in hybrids ofS×B （16.48%-49.84%） and S×X （14.26%-52.62%） were higher than that ofreverse hybrids B×S or X×S for the four growth traits, yet the shell width of thehybrids B×S showed the lowest heterosis rate （0.24%）. Heteroses of body weightwere the highest among the four traits for all crosses. ANOVA of the four growth traitsshowed no significant difference among within-population crossing BBF₁, XXF₁andSSF₁. Results of LSD indicated that there was a significant difference in the four growthtraits between crossbreds and purebreds. There was significant difference in the four growth traits between the crossbred of S×B or S×X and purebreds. Among thesix crossbreds, there were very significant differences in the four growth traits, whilethere were great significant differences in traits between hybrids of S×B, S×X andother hybrids. The hybrids of X×B and X×S had significantly greater values ofbody weight, and they had very significant greater values of shell length, shell width andshell height. The six genetic-improved crossbreds can be used as the basic populations tobreed new varieties.4. Microstructure of the gill in the pearl oyster Pinctada fucataThe pearl oyster Pinctada fucata is a typical filter feeder, and is also an importantmarine pearl-producing oyster. Yet, the structure of gills, the feeding organ, remainsunknown. In this study, the histological structure of the gill tissue in P. fucata wasstudied by using light and electronic microscopies for the first time. The gill of theanimal belongs to heterorhabdic gill type, which is composed of two pieces of gilllamellas on each side of the shell cavity, i.e. inner and outer gill lamellas. The gilllamella is consisted of two kinds of gill filaments, principal and normal gill filaments.The principal filaments play a supporting role in the demibranch. Nine to twelve normalgill filaments are grouped into a cluster by intrabunchial junctions between every twoprincipal gill filaments. The normal gill filaments are linked by interfilament junctions.The epithelial cells of the interfilament junctions are a kind of flat respiratory epithelialcells, the same as that of the normal gill filaments. The existence of the interfilamentjunctions expands the surface area of the gill, which is helpful for air exchanging. Thefrontal cilia and lateral cilia on the surface of the gill filaments are responsible forcarrying food particles and exchanging air. The superficial cilia of normal gill filamentsis typically structured by “9+2” microtubules. The results above provide a backgroundfor further research on the relationship between the structure and function of gills in thepearl oyster P. fucata.