Comparison of growth and survival of larvae among different shell color stocks of bay scallop Argopecten irradians irradians(Lamarck 1819)

In order to improve production and breed new broods of bay scallop Argopecten irradians irradians, different-colored orange, purple and white lines were established by two mating methods of self-fertilization and mass spawning at a commercial scallop hatchery in spring, 2002. And then larval growth and survival of different lines was compared to test whether there is a relationship between shell color and growth and survival at early developmental stage. Both growth and survival have no significant differences among different experimental larvae of self-fertilization or mass spawning. Results are as following in the order of orange, purple and white shell stock. For the self-fertilization, growth rates of larvae were 6.174, 6.412, and 6.599 μm/d, respectively. Survival rates of larvae at Day 3 were 74.41%, 76.86%, and 82.05%; Day 6 were 49.14%, 65.63%, and 52.79%; and Day 9 were 25.06%, 20.80%, and 26.47%, respectively. For the mass spawning, the growth rates were 7.836, 7.941, and 7.878 μm/d, respectively. Survival rates at Day 3 were 93.05%, 91.95%, and 92.50%; Day 6 were 79.17%, 78.05%, and 82.50%; and Day 9 were 34.72%, 36.67%, and 38.33%, respectively. The absence of any relationship between shell color and growth and survival at the larval stage may be resulted from their common genetic basis.

Effects of effective population size on the F_2 growth and survival of bay scallop Argopecten irradians irradians (Lamarck)

In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups （Ne=10, 30, 50, control）, and there were no significant differences among the latter （P〉0.05）. At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group （P〈0.05）. These results indicated that the low effective population size （Ne）, which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Fta＇thermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.

Quantitative traits correlative analysis and growth comparison among different populations of bay scallop,Argopecten irradians

The shell traits and weight traits are measured in cultured populations of bay scallop, Argopecten irradians. The results of regression analysis show that the regression relationships for all the traits are significant (P<0.01). The correlative coefficients between body weight, as well as tissue weight with shell length, shell height and shell width are significant (P<0.05). But the correlative coefficients between the anterior and posterior auricle length with body weight as well as tissue weight are not significant (P>0.05). The multiple regression equation is obtained to estimate live body weight and tissue weight. The above traits except anterior and posterior auricle length are used for the growth and production comparison among three cultured populations, Duncan's new multiple range procedure analysis shows that all the traits in the Lingshuiqiao (LSQ) population are much more significant than those of the other two populations (P<0.01), and there is no significant difference between the Qipanmo (QPM) and Dalijia (DLJ) populations in all traits (P>0.05). The results indicate that the LSQ population has a higher growth rate and is expected to be more productive than the other two populations.

Screening microsatellite markers from EST sequences of bay scallop Argopecten irradians

Seventy-five simple sequence repeats （SSRs） were identified by the bioinformatic analysis from 5008 expressed sequence tags （ESTs） of Argopecten irradians. Among the SSRs, the number of repeat nucleotide varied from 2 to 6. Dinucleotide and trinueleotide repeat motifs were dominant in EST-SSRs of bay scallop, with a proportion of 80% over the total screened SSRs. Twenty-nine pairs of primer were designed based on the flank sequences of the selected ESTs using the software of Primet 5, and verified under the given PCR reaction condition. Eighteen of the 29 primer pairs resulted in the expected products, while the remaining either failed to produce any fragments or yielded products over expected size. Thirteen of the 18 SSRs, accounting for 72%, were detected to show polymorphism in the examined scallop samples. A preliminary test in this study indicated that the majority of the identified SSRs were informative in the cultured bay scallops, making them suitable for the population and other genetic analysis. EST-SSR markers have more advantages than the traditional genomic-derived SSRs and there is a wide range of application in comparative mapping, functional gene cloning and marker assisted selection. This research provides a reference to the identification of EST-SSRs with relative bioinformatic analysis from aquaculture species, as well as to those with a large number of ESTs.

The effect of the causative algae of large-scale HAB in the East China Sea on egg hatching of Argopecten irradians, and population growth of Brachionus plicatilis and Moina mongolica

The impacts of Prorocentrum donghaiense Lu and Alexandrium catenella Balech, causative species of the large-scale HAB in the East China Sea, were studied under laboratory conditions. According to bloom densities, the effects of monocuhure and mixture of the two species were examined on the egg-hatching success ofArgopecten irradiarts Lamarck, and the population growth of Brachionus plicatilis MUller and Moina mongolica Daday. The results showed that monocuhure of A. catenella had a significant inhibition on the egg hatching success of A. irradians, and the population growth of B. plicatilis and M. mongolica. The median effective densities （ED50） inhibiting the egg hatching success of A. irradhms for 24 h and the population growth of B. plicatilis and M. mongolica for 96 h were 800, 630, and 2 400 cells/cm^3 , respectively. Monoculture of P. dongha/ense has no such inhibitory effect on the egg hatching success of A. irradians; P. donghaiense at lower suitable densities could sustain the population growth of B. plicatilis （ 1 × 10^4 ～ 3 ×10^4 cells/cm^3 ） and M. mongolica （2 × 10^4～5 ×10^4 cells/cm^3 ） ; P. donghaiense at higher densities had significantly adverse effect on the population growth of B. plicatilis （4 × 10^4 ～ 10×10^4 cells/cm^3 ） and M. mongolica （ 10 ×10^4 cells/cm^3）. When the two algae were mixed according to bloom densities, P. donghaiense at suitable densities to some extent could decrease the toxicity of A. catenella to B. plicatilis and M. mongolica. The results indicated that the large-scale HAB in the East China Sea could have adverse effect on zooplankton, and might further influence the marine ecosystem, especially when there was also Alexandrium bloom.

Responses to two-way selection on growth in mass-spawned F_1 progeny of Argopecten irradians concentricus(Say)

In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop （Argopecten irradians concentricus） was examined to evaluate the efficacy of a selection program currently being carried out in Beibu Bay in the South China Sea. A total of 146 adult scallops were randomly selected from the same cultured population ofA. i. concentricus, and divided into two groups in shell length （anterior-posterior measurement）： large （4.91-6.02 cm, n=74） and small （3.31-4.18 cm, n=72）. At the same time, a control group was also randomly sampled （4.21-4.88 cm, n=80）. Mass-spawned F1 progenies from the three size groups were obtained and reared under identical conditions at all growth phases. The effects of two-way （or upward-downward） selection on fertilization rate, hatching rate, survival rate, daily growth in shell length and body weight were assessed in the three size groups. Results show that significant differences （P〈0.01） were found in hatching rate, survival rate and daily growth of F~ progenies, but not in fertilization rate （P〉0.05）, among the three groups. The hatching rate, survival rate and daily growth of the progeny of large-sized parents were greater than those of the control group （P〈0.05）, which in turn were larger than those of small-sized group （P〈0.05）. Responses to selection by shell length and body weight were 0.32±0.04 cm and 2.18±0.05 g, respectively, for the upward selection, and -0.14±0.03 cm and -2.77±0.06 g, respectively, for the downward selection. The realized heritability estimates of shell length and body weight were 0.38±0.06 cm and 0.22±0.07 g for the upward selection, and 0.24±0.06 cm and 0.37±0.09 g for the downward selection, respectively. The change in growth by bidirectional selection suggests that high genetic variation may be present in the cultured bay scallop population in China.

A prokaryotic mycoplasma-like organism infection in the scallop Argopecten irradians

Intracytoplasmic infection with a prokaryotic mycoplasma-like organism （MLO） were characterized in the scallop Argopecten irradians, and the first report of such infection in this scallop was represented. Ultrastructurally these microorganisms are usually pleomorphic and variable in morphology and size, and appear in several cell types such as small spherical body, rod-shaped bodies and longer filament-shaped body. They lack a cell wall. These observations revealed that these types of the prokaryote showed some characteristics of a mycoplasma-like organism （MLO）. MLO reproduced in two ways： binary fission and budding. The results of isolation and purification showed that a large number of MLOs existed in the tissues of diseased scallops. The results of experimental infection revealed that the MLO is pathogenic to the scallop Argopecten irradians.

CYTOLOGICAL COMPARISON OF GAMETOGENESIS OF SCALLOPS,ARGOPECTEN IRRADIANS AND CHLAMYS FARRERI

Histological characteristics of gametogenesis of two kinds of scallops, gonochoric Chinese scallop, Chlamys farreri and hermaphroditic bay scallop, Argopecten irradians were investigated in this study. Spermatogenesis in C. farreri has different developmental stages: spermatogonia, primary spermatocyte, second spermatocyte, spermatid and spermatozoon. A large number of same developmental stage spermatic cells converge at a definite area of the testis. Premeiotic, previtellogenic and vitellogenic oocytes can be found during oogenesis in C. farreri , where oocyte distribution is obviously irregular. The A. irradians gonad consists of two different parts in one individual: one part functions as testis, the other as ovary. Between these two parts is a special appearance area, where a large number of spermatic cells are bound with two layers of acellular substance with many oocytes in it.

Effect of E. coli coli on Anti-disease Activities of Scailops: Argopecten irradians

The effect of acute E. coli challenge on the anti-disease activity of scallops Argopecten irra-dians is examined. The treatments of scallop from which hemolymph samples were taken for study included (1) control scallops, (2) sham-injected scallops, (3) PSW-injected scallops and (4) E. coli-injected scallops. From the beginning, the anti-disease activities of scallops are deter -mined at 12 hr and 24 hr.The concentrations of circulating hemocytes, the total serum protein concentrations and the activities of alkaline phosphatase, acid phosphatase and superoxide dismutase in the scallops Argopecten irradians are determined.Injection with E. coli results in a significant elevation in the concentration of circulating hemocytes and in the alkaline phosphatase activity and a significant decline in the total serum protein concentration and in the superoxide dismutase activity at 24 hr postchallenge. It shows that metabolism of bay scallop is expedited to adopt the challenge.

海湾扇贝、刺参、魁蚶间作立体混养模式试验

为充分利用水体空间,降低养殖成本,在海洋牧场海域进行了海湾扇贝(Argopecten irradians)、刺参(Stichopus japonicus)、魁蚶(Scapharca broughtonii)间作立体混养试验,形成由不同营养级生物组成的综合养殖系统。苗种增殖后对试验海域和非试验海域进行了水质监测,结果显示,苗种增殖对试验海域没有造成污染,而三个水产品种的滤食特性对水质有一定的改善。统计三个水产品种收获情况,海湾扇贝、刺参和魁蚶产量分别为11000 kg/hm^(2)、767.59 kg/hm^(2)和1302 kg/hm^(2)。试验证明,海湾扇贝、刺参、魁蚶间作立体混养模式不仅具有较好的生态效益,同时具有显著的经济效益。

“青农2号”海湾扇贝池塘保苗技术

在海湾扇贝养殖阶段,稚贝保苗是关键技术之一,是提高扇贝产量的基础。“青农2号”海湾扇贝是一种生长速度快、贝柱出肉率高的扇贝新品种。本文利用池塘保苗技术培养“青农2号”海湾扇贝,并对保苗水质保障、保苗网箱的选择、刷苗操作和商品苗运输等环节进行了探索和讨论。实践表明,3亿粒左右的稚贝,经过50 d左右的池塘保苗,稚贝平均日生长速度90μm左右,平均规格达到5 mm,全池共生产商品苗6000万粒,保苗成活率20%左右。

Cytogenetic analysis in two scallops (Bivalvia:Pectinidae) by PRINS and PI banding

Cytogenetic analysis was performed for the bay scallop （Argopecten irradians Lamarck 1819） and the Japanese scallop （Patinopecten yessoensis Jay 1857 ） by primed in situ labeling （PRINS） and propidium iodide （PI） banding techniques. The PRINS analysis revealed that major rRNA genes were clustered in two loci on the telomeric regions of the short arms on two acrocentric chromosome pairs in A. irradians and on two submetacentric pairs in P. yessoensis. The histone H3 gene sites differed in number and location between these two species. The C-band-like patterns revealed by PI staining varied considerably between these two species. A. irradians displayed terminal bands at long arms on all chromosomes, centromeric bands on some pairs and interstitial bands on five pairs. P. yessoensis exhibited only centromeric bands on all chromosomes. These results would contribute to the better understanding of karyotype evolution in A. irradians and P. yessoensis.