| Pearl oyster, Pinctada fucata, is the main pearl oyster to produce the pearl in theworld, it mainly distributes in tropical and subtropical areas. This experimentsconstructed selected families using different geographical populations of the pearloyster P. fucata, and the growth performances were analyzed to provide a baseline forselective breeding. We also compared the growth and survival of P. fucata cultured indifferent types of cages and water depth.Pearl oyster P. maxima is the only oyster that produces South Sea pearls, the largestamong others. However, marine pollution and other problems, high mortality occurredin recent years. This article started some experiments for measuring the filtration rateunder different environmental factors using the pearl oyster spat, aiming to provide atheoretical basis and new methods for improvement of culture technique. The mainresults were as follows.1. The growth performance of selected families of Pinctada fucataUsing the pearl oyster collected from Xuwen (X) and Sanya (S), a2×2diallelehybrid crosses were constructed in Tropical Marine Research and Development Centersof South China Sea Fisheries Research Institute in March2010, and a total of30F1generation families was obtained, which contained4combinations: reciprocal crosses(S?×X?) and (X?×S?), and selfing crosses (S?×S?) and (X×X).Statistics showed that heterosis was observed in the crossbreds as compared withpurebreds in shell height, shell length, shell width and body weight, with the rangebetween0.45%-49.18%, and the heterosis in body weight was the biggest in the fourtraits. The order of the growth performances of the four traits was forward crosses (S×X)> reverse crosses (X×S)> the Xuwen selfing crosses (X×X)> Sanya selfingcrosses (S?×S). It provides a theoretical basis for the selective breeding of the pearl oyster P. fucata based on growth performance analysis.2. The effects of culture cages on the growth performances of P. fucataThe effect of different shapes of cages on the growth of P. fucata juveniles wasstudied using offsprings reproduced by Sanya parent () and Xuwen parent () inAugust2011. The shapes of cages included rectangular, cylindrical and hemisphericalcages, with sizes of20cm×12cm×15cm, radius (r) of11.5cm×15cm (H), and radiusof15cm for the three types of cages, respectively. The culturing depth ranged from2mto7m underwater with1m interval in Xincun Bay, Lingshui County, Hainan Province.The numbers of the juvenile oysters were74ind./cage in rectangular cages,102ind./cage in cylindrical cages, and150ind./cage in hemispherical cages. The densitywas0.053ind./cm2for all kinds of cages based on surface area. Under the conditionsabove, the growth rates of shell length (SL) and body weight (BW) reach the highest atthe water depth of4m for rectangular cages, being24.55%and6.44%, respectively,significantly higher than those at the other water layers (P<0.01). The highest growthrates of SL and BW occur at3m deep for hemispherical cages, being22.55%and5.40%, respectively, significantly different from the other depths (P<0.01), while occurat6m deep for cylindrical cages, being22.46%and5.37%, respectively, significantlyhigher than the3,5,7m depths (P<0.01). There were no significant differences amongthe other groups. In addition, the heights of the cages also impact on the growth of P.fucata juveniles for cylindrical and rectangular cages. The growth rates of shell height(SH) and BW got the highest at the height of20cm, being24.70%and6.20%,significantly different from those with5cm,10cm and15cm high cages (P<0.05) forcylindrical cages. Also the growth rate of SL was the greater at the cage height of10cmfor rectangular cages, but there was no significant difference from each other. Theresults showed that the best growth performances could be obtained by using11.5cm (r)×20cm (H) cylindrical cages or20cm (L)×12cm (W)×10cm (H) rectangular cages.In terms of cost, cylindrical cage is cheaper than rectangular cage.3. The effects of culturing water depth on the growth and survival of P. maximaThe spats of the pearl oyster P. maxima were cultured using submersible lines infive different depth, recording the hydrological factors in mariculture area, measuringthe two traits, shell length and shell height, and comparing the survival in differentwater layers. The results showed that high growth rates were obtained at4m,5m,6m water layer, and there was no significant difference from each other (P>0.05). Shellgrowth rate was slower at2m and3m depth. There was significant difference (P<0.05)between3m water layer and4m,5m,6m in shell length. The survival rate of P.maxima was the highest when cultured in5m depth, and the second was in4m depth.The lowest survival rate (52%) was in2m water depth. This study provides a basis fornew farming method for the pearl oyster.4. The effects of ecological factors on the filtration rate of P. maximaThe effects of salinity and algae species and its concentration on the filtration ratesof juvenile silver lip pearl oysters (Pinctada maxima) were studied using clearancemethod in a static system. In natural sea water (33, T=28℃), the filtration rates increasewith the increase of Isochrysis galbana concentrations (0.5×10~5,1×10~5,1.5×10~5,2.0×10~5,2.5×10~5) at first and then decrease with the maximum (0.069±0.008L/h, n=3)appearing at1.5×10~5cell/mL. The correlation between filtration rates and algaeconcentrations could be expressed by the power function: y=0.0098x0.7097(r=0.9935).The maximum was0.0636±0.007L/h (n=3) when salinity was at30. In salinity of30,the filtration rates at1,2,3or4hours after feeding P. subcordiformis (0.8×10~5cell/mL)or Isochrysis galbana (1.5×10~5cell/mL) showed that the filtration rate of the juvenilepearl oysters on the Isochrysis galbana was greater than that on P. subcordiformis at thefirst two hours, and then become nearly equal (0.046±0.001L/h v.s.0.051±0.003L/h(n=3)) at3h, and then less than that on P. Subcordiformis. The filtration rates of thejuvenile pearl oysters on the microalgae, P. subcordiformis (0.8×10~5cell/mL) increasefirstly and then decrease with the increase of salinity (24,27,30,33,36), with thehighest (0.0636±0.007L/h, n=3) occurred at the salinity of30. |
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