Genetic linkage map of bay scallop, Argopecten irradians irradians (Lamarck 1819)

The bay scallop (Argopecten irradians irradians Lamarck 1819) has become one of the most important aquaculture species in China. Genetic improvement of cultured bay scallop can benefit greatly from a better understanding of its genome. In this study, we developed amplified fragment length polymorphisms (AFLPs) and simple sequence repeat markers from expressed sequence tags (EST‐SSRs) for linkage analysis in bay scallop. Segregation of 390 AFLP and eight SSR markers was analysed in a mapping population of 97 progeny. Of the AFLP markers analysed, 326 segregated in the expected 1:1 Mendelian ratio, while the remaining 74 (or 19.0%) showed significant deviation, with 33 (44.6%) being deficient in heterozygotes (A/a). Among the eight polymorphic EST‐SSR loci, one marker (12.5%) was found skewing from its expected Mendelian ratios. Eighteen per cent of the markers segregating from female parent were distorted compared with 21% of the markers segregating from male parent. The female map included 147 markers in 17 linkage groups (LGs) and covered 1892.4 cM of the genome. In the male map, totally 146 AFLP and SSR markers were grouped in 18 LGs spanning 1937.1 cM. The average inter‐marker spacing in female and male map was 12.9 and 13.3 cM respectively. The AFLP and SSR markers were distributed evenly throughout the genome except for a few large gaps over 20 cM. Although preliminary, the genetic maps presented here provide a starting point for the mapping of the bay scallop genome.     

SNPs of myostatin (MSTN) gene and their association with growth traits in three bay scallop (Argopecten irradians) populations

Genetic diversity and correlation analysis between single nucleotide polymorphism (SNP) of myostatin (MSTN) gene and the growth traits were performed in Argopecten irradians. Around 279 individuals from three A. irradians populations were screened for the polymorphic sites of the MSTN gene. Two SNPs were found: T910G and G1162A. The observed heterozygosity of the two SNPs ranged from 0.1310 to 0.3299, whereas the expected heterozygosity ranged from 0.1436 to 0.2973. The values of D′ and r² of linkage disequilibrium (LD) ranged from 0.475 to 1.0 and 0.052 to 0.174 respectively. Association analysis shows that individuals with genotype TT and TG of locus W4 had significantly higher adductor muscle mass than that with genotype GG in population CA (P < 0.05). Individuals with genotype AA of locus W5 had significantly higher body mass, soft‐tissue mass, adductor muscle mass, shell width and shell mass than those of other genotypes in population RZ (P < 0.05). The two SNPs found in our study can be used for molecule marker‐assisted breeding of A. irradians.     

海湾扇贝病原菌-黑美人弧菌的分离与致病性

1997年8～9月,大连金州区大李家乡养殖场筏养海湾扇贝(Argopectenirradians)突发大面积死亡。其主要病症是外套膜收缩,重者全部脱落,鳃丝呈土黄色或糜烂,肠管空并伴有不同程度的肾肿胀。从病贝血淋巴液和鳃组织中分离的2株优势菌(h9701-1,g9701-2)分别做纯培养,采用肌注法感染健康贝,得到与原发病相同症状,证实是病原菌。经多项形态、生理生化测定,2株分离菌皆是黑美人弧菌(Vibrionigripulchritudo)。     

Crosses between two subspecies of bay scallop Argopecten irradians and heterosis for yield traits at harvest

In order to improve the yield of bay scallop Argopecten irradians by exploiting geographic subspecies heterosis, crosses between and within two subspecies, the northern A. i. irradians (Lamarck) and the southern A. i. concentricus (Say), were created and the offspring were cultured under the same environmental conditions. The two parental populations were collected from Bohai Bay in northern China and Beibu Bay in southern China, which were distinct in particular shell colours. The results indicated that the shell colour of bay scallop was inheritable and could be used as a morphological mark to distinguish hybrid and purebred individuals. At harvest, hybrid offspring always produced a significantly higher yield than purebred offspring. Positive heterosis was achieved for shell length, shell height, shell width, total weight and adductor weight, which was 5.02, 5.22, 3.88, 7.53 and 9.47 respectively. Hybrid gain was 10.86% for shell length, 10.48% for shell height, 9.77% for shell width, 34.90% for total weight and 41.69% for adductor weight, respectively, and all were significantly >5%. The present study reveals that it is effective for improving yield by hybridization between different geographic subspecies in the bay scallop.     

Production of a base population and its responses to F1 selection in the bay scallop, Argopecten irradians irradians Lamarck (1819)

A base population of the bay scallop, Argopecten irradians irradians Lamarck, was produced by crossing two cultured bay scallop populations. After 1 year of rearing, the top 10% truncation selection of the top 10% ( i =1.755) was carried out in the base population of about 1300 adults. A control parental group with a an identical number to the select parental group was randomly selected from the entire population before isolation of the select parental group. The result showed that, at the larval stage, the growth rate of larvae in the selected line was significantly higher than that of the control ( P <0.05), and that the genetic gain was 6.78%. Owing to the lower density of control at the spat stage, the mean shell length of the control line was larger than that of the select line at day 100. When the same density was adjusted between two lines in the grow-out stage (from day 100 to 160), the daily growth rate of the selected line was significantly higher than that of the control line ( P <0.05). Survival of the select line was significantly larger than that of the control line in the grow-out stage. In conclusion, the results obtained from this experiment indicate that selective breeding from a base population with a high genetic diversity established by mass spawning between different populations appears to be a promising method of genetic improvement in bay scallop, A. irradians irradians Lamarck.     

Strategies for enhancement of natural bay scallop, Argopecten irradians irradians, populations; A case study in the Niantic River estuary, Connecticut, USA

We investigated strategies to enhance populations of bay scallops,Argopecten irradians irradians (Lamarck, 1819), in a presumablyrecruitment-limited natural habitat. At present, the Niantic Riverestuary supports only a minor bay scallop population that is harvestedrecreationally. Three enhancement strategies were evaluated; (1)collection and redistribution of natural spatfall, (2) introduction andover-wintering of hatchery-reared stock into natural habitat to providenew spawning stock, and (3) over-wintering of hatchery-reared stock insuspension culture for creation of mobile spawner sanctuaries. Anassessment of natural bay scallop recruitment in the Niantic Riverconducted in 1997 indicated that few spat were found, they were widelydispersed within the river, and peak spawning occurred in late July1997. Direct re-seeding was evaluated as an enhancement measure byplanting hatchery-reared scallops ( 38 mm shell height) insmall-scale, 100-m² plots at different times and densities.Time of planting and the inferred predation intensity were major factorsaffecting survival; whereas, planting density had no significant effect.Approximately 9,000 scallops (35–45 mm shell height), broadcastwithin an eelgrass bed in November 1997, had high over-winter survivaland underwent gametogenesis and spawning during 1998. Of 26,000 bayscallops ( 45 mm shell height) over-wintered in suspensionculture from 1998–1999, approximately 60–80%survived, and these scallops spawned in mobile sanctuaries, during thesummer of 1999. There is good potential for using aquacultural methodsfor enhancement of bay scallop populations when natural recruitment ispoor and habitat and environmental conditions are not limiting.     

影响海湾扇贝中间育成效果的因素探讨

影响海湾扇贝中间育成效果的主要因素有:育成器具种类(A)、换袋时间(B)、网孔大小(C)和装苗量(D)。正交试验和方差试验表明,A、C、D为提高保苗率的敏感因素,B、C、D为提高生长效果的显著因素。试验结果提出:网箱或圆锥形袋的保苗率明显优于扁袋;每隔15～30天更换一次网袋可显著加快贝苗的生长速度,网孔大小以2mm为适宜,每袋最终实际装苗量应在2000只以内。     

Recruitment of catarina scallop (Argopecten ventricosus) larvae on artificial collectors off the NE coast of the Gulf of California

We evaluated recruitment of larvae of catarina scallop, Argopecten ventricosus, in the area of Puerto Peñasco, NE Gulf of California. We moored artificial collectors in six sites from June 2007 to August 2008 and replaced them every 2 months. We used monthly (July 2002–September 2011) sea surface temperature (SST, °C) and surface chlorophyll‐a concentration (SSChl, mg m^?3) Aqua/MODIS satellite data to describe seasonal environmental behaviour study area. Also, we recorded bottom temperature at each site every 4 h, and every 2 months measured sea surface salinity, temperature and dissolved oxygen. We used a repeated measures anova to evaluate differences in the number of recruited spat between main factors, and analysed the presence of multimodal spat shell size frequency distributions. Overall, spat recruitment was negatively correlated with seawater temperature and showed higher spat recruitment abundances throughout winter, which is the season with the highest surface chlorophyll a concentration. We estimated multimodal shell size frequency distributions characterized by more than one modal size. The natural collection of A. ventricosus spat on artificial collectors in the area can be successfully performed over a protracted period (November–December to May–June). Our results extend the area where collection of A. ventricosus spat can be successful.     

Effect of florfenicol and oxytetracycline treatments on the intensive larval culture of the Chilean scallop Argopecten purpuratus (Lamarck, 1819)

The administration of antimicrobials to control bacterial pathologies in Chilean scallop hatcheries is a frequent practice, but their effects on these cultures remained unknown. This study was undertaken to obtain information on the effect of the administration of florfenicol and oxytetracycline on the growth, survival and bacterial content of scallop larvae under farming conditions. Florfenicol‐treated cultures exhibited high survival rates (44% after 17 days of culture), whereas cultures not treated or treated with oxytetracycline collapsed after 11 days of culture. Surprisingly, no significant differences in the heterotrophic (Tukey test; P = 0.226) and Vibrio (Tukey test; P = 0.666) concentrations between the oxytetracycline‐treated and untreated larval cultures were observed. Otherwise, florfenicol administered directly into rearing tanks produced significantly higher larval growth (Tukey test; P = 0.0001) and survival (Tukey test; P = 0.011) than bath treatment. When 2 and 4 mg L^?1 of florfenicol were compared, no significant differences in growth (t‐test; P = 0.4596) and survival (Tukey test; P = 0.057) were observed, suggesting that a concentration of 2 mg L^?1 is sufficient to ensure larval production. The present results demonstrate the efficacy of florfenicol‐based therapy to increase larval survival and growth at commercial scale and prompt the necessity to standardize its use in Chilean scallop hatcheries.     

Efficacy of Netminder® silicone release coating for biofouling reduction in bay scallop grow‐out and comparative effects on scallop survival,growth and reproduction

Netminder^®, a water‐based silicone barrier release coating, was highly effective in reducing biofouling of lantern nets during grow‐out/overwintering of bay scallops, Argopecten irradians irradians, in a large‐scale restoration programme in New York, USA. Compared with untreated nets, scallops held in Netminder^®‐coated nets experienced reduced survival after 8 months, probably due to higher loads of epibionts on their shells. However, this was countered by higher reproductive and overall condition of scallops in treated vs. untreated nets; there were no consistent differences in shell growth in different net treatments. Although further testing is recommended under a wider range of conditions, we conclude that for the purposes of our scallop restoration work, coating nets with Netminder^® would eliminate the need for a gear change in spring, thus reducing labour costs; the coating process should be refined so that Velcro closures of nets do not become sealed shut.     

Breeding cycle of the northern scallop, Argopecten purpuratus (Lamarck, 1819) in southern Chile

The gametogenic cycle of the northern scallop, Argopecten purpuratus (Lamarck, 1819) was studied in southern Chile. This species has a high commercial value and is cultivated in northern Chile, the location of its natural habitats. It has recently been introduced into southern Chile where advantages such as suitable sheltered locations protected from wave action favour its mass culture. However, there are also potential disadvantages, such as lower water temperatures, which could affect reproduction. The results of the monthly variations of the gonadosomatic index and the frequency of maturity stages in specimens cultivated in Metri Bay (41° 36′S; 72° 43′W) and in those kept on the seabed in Quihua Channel (41° 50′S; 73° 05′W), suggest that the maturity and spawning period of this species extends from the end of spring through autumn. This pattern was more pronounced in Metri Bay, where levels of maturity were higher, due to higher summer water temperatures, than in Quihua Channel. Specimens at different maturity stages are found throughout the year, which seems to be associated with a rapid gonad recovery. The general pattern of the gametogenic cycle of specimens in the cultures does not differ from that recorded in the natural habitat of the species. The data available suggest that during reproduction temperature changes are more important than the relative values of the temperature. This evidence would support the possibility of mass culture of this species in southern Chile, outside its natural distribution area that extends from Corinto, Nicaragua (12°S) to Valparaíso, Chile (33°S).     

The culture of the southern bay scallop in Tampa Bay, an urban Florida estuary

Bay scallop, Argopecten irradians concentricus (Say), stocks were collected from a Homosassa (Florida) population in 1991 and were kept in seawater from Bayboro Harbor on Tampa Bay, an urban Florida estuary. They were fed with Isochrysis galbana and Tetraselmis sp. Spawning was allowed to occur after the scallops became ripe. The hatching rate of the F1 eggs to D-shaped larvae was 72%. Settlement and metamorphosis began 11 days after fertilization. When spat reached a shell height of 0.8 mm in the laboratory, they were placed with substrates into 300 and 800 m mesh bags, and later in lantern nets, suspended from a dock in Bayboro Harbor. The F1 scallops successfully survived to gonad maturity in the fall of 1992, with mean (sd) shell height of 49.8 (4.0) mm on 6 September 1992. The scallops experienced heavy mortality during the summer, partially as a result of heavy fouling. From early August to October of 1992, F1 scallops grown in Bayboro Harbor were successfully spawned in the laboratory. Growth and survival of the F2 scallops were comparable to those of the F1 scallops. Results have shown that bay scallops can complete an entire life cycle in an urban estuary such as Tampa Bay, and a hatchery for bay scallops on the estuary can assist in the restoration of the population. Fouling represents a possible severe limitation and alternatives to caging for grow-out should be considered.     

Chlamydia-like organisms in the digestive diverticula of the bay scallop, Argopecten irradians (Lmk)

Abstract. The morphology of a chlamydia-like organism from the digestive diverticula of the bay scallop, Argopecten irradians (Lmk), is described. This organism was found in about 40% of bay scallops introduced to the quarantine unit at Ellerslie, Prince Edward Island, Canada and also in about 40% of the F₁ and F₂ generations. Procaryote infections were also found in the northern quahog, Mercenaria mercenaria (L.), the soft-shelled clam, Mya arenaria L., and the Atlantic deepsea scallop, Placopecten magellanicus (Gmelin).     

Effect of parental stock size on F1 genetic structure in the bay scallop, Argopecten irradians (Lamarck, 1819)

Three F₁ families of the bay scallop, Argopecten irradians, were produced from one, two and 10 individuals. The genetic changes in these populations, which suffered recent and different levels of bottleneck, were analysed using amplified fragment length polymorphism (AFLP) techniques. In the parental stock, a total of 330 bands were detected using seven AFLP primer pairs, and 70% of the loci were polymorphic. All F₁ groups had a significantly lower proportion of polymorphic loci when compared with the initial stock, and loss of the rare loci and reduction in heterozygosity both occurred. The progeny of the larger population (i.e., N=10) exhibited a lesser amount of genetic differentiation compared with the progeny from N=2, which showed lesser differentiation than progeny from N=1. The effective population sizes (N_e) in N=1, 2 and 10 were estimated as 1.50, 1.61 and 2.49. Based on regression analysis, we recommend that at least 340 individuals be used in hatchery populations to maintain genetic variation.     

The influence of temperature and presence of predators on growth,survival and energy allocation for reproduction in the Catarina scallop Argopecten ventricosus

Environmental factors are known to modify the life history of marine ectotherms. In a 16‐month laboratory experiment, we investigated the influence of temperature and presence of predators on life‐history parameters including shell growth, survival and the energy investment in reproduction and body mass of the short‐lived (2–3 years) scallop Argopecten ventricosus. In parallel, A. ventricosus was maintained in the field at the Pacific coast of Baja California, México, to compare growth, survival and reproductive effort under natural conditions. For the laboratory treatments, scallops were reared at simulated field temperatures (SFT), 5 °C above SFT and in the presence of predators. Elevated water temperatures caused higher growth and gonad production, although at the cost of increased mortality. Presence of predators induced energy allocation to muscle rather than gonad growth, deferred spawning and extended survival. Field scallops exhibited higher growth, higher reproductive investment and were able to reproduce twice, whereas all laboratory scallops died after the first spawning. The natural variability of environmental parameters such as food and temperature may thus support optimal growth in the field, and when animals are protected from predators, reproduction in the second year of life.     

Comparison of early life history stages of the bay scallop, Argopecten irradians: Effects of microalgal diets on growth and biochemical composition

The culture of bay scallops, Argopecten irradians, is limited by a reliable and affordable supply of spat and the ability to ensure that animals attain market size within a single growing season. The main goals of our study were thus: (1) to develop growth-optimizing algal diets for implementation in hatcheries, and (2) to identify and compare bay scallop postlarval and juvenile dietary requirements, especially of lipids and fatty acids, which if met may enhance production. Nutritional needs of postlarval bay scallops (present study) are compared with those of sea scallops, Placopecten magellanicus, offered the same diets in a previous companion study. To this end, postlarval (initial shell height, SH = 240 μm) and juvenile (initial SH = 10 mm) bay scallops were offered 6–7 microalgal diet combinations at 20 °C, for 3 weeks. A similar growth ranking among diets was observed between the two developmental stages. A combination diet of Pavlova sp. (CCMP 459) and Chaetoceros muelleri was far superior to any other diet tested, yielding growth rates of 58 and 357 μm day^− 1 which were 65% and 25% higher than the next highest performing diet of Tetraselmis striata/C. muelleri in postlarvae and juveniles, respectively. The T. striata/C. muelleri diet, which is limited in the n-3 fatty acid docosahexaenoic acid (DHA), yielded very poor growth of sea scallop postlarvae in a prior study, indicating that bay scallops may have less stringent requirements for DHA than sea scallops. The Pav 459/C. muelleri diet, which also supported the highest growth of sea scallop postlarvae, is characterized by elevated levels of the n-6 fatty acids, arachidonic (AA) in C. muelleri and 4,7,10,13,16-docosapentaenoic (DPA) in Pav 459. The two diets deficient in AA and n-6 DPA, Pavlova lutheri/Thalassiosira weissflogii and P. lutheri/Fragilaria familica, yielded the lowest growth rates in both bay scallop postlarvae and juveniles. Tissue enrichment of these two fatty acids relative to the diet, as well as overall enrichment in ∑n-6 fatty acids was observed across developmental stages and dietary treatments. A similar pattern has previously been observed in sea scallop postlarvae, suggesting a dietary requirement for n-6 fatty acids in pectinids that has often been overlooked in the past.     

海湾扇贝南部亚种闭壳肌质量的双性状选择效应

采用双性状选择方法在经群体继代大壳高选育的海湾扇贝(Argopecten irradians concentricus Say)南部亚种F₃养殖群体中进行闭壳肌定向选育, 以评价闭壳肌的选择效果和现实遗传力, 为海湾扇贝南部亚种育种提供理论依据。结果表明, 在以壳高为第一选择性状、体质量为第二选择性状、壳高选择压力为10%、体质量选择压力为1%情况下, 正、负向选择组、对照组在产卵量、受精率、孵化率、幼虫期壳长增长率、中培期存活率、成体各形态参数等方面的差异不显著(P>0.05); 在稚贝育成率、养成期存活率、成体各质量性状等方面均存在显著差异(P<0.05), 各指标值均呈现正向选择组>对照组>负向选择组; 正、负向选择组中, 体质量与闭壳肌质量均出现较高的现实遗传力, 且正向选择组高于负向选择组; 双性状选择时, 体质量与闭壳肌质量的当代遗传获得明显高于单性状选择结果。壳高和体质量对闭壳肌质量均具有密切的遗传相关, 任何一个性状的选择均可对闭壳肌质量产生显著影响, 双性状同时选择可对闭壳肌质量产生叠加效应, 使闭壳肌质量性状的遗传进展达到最大。

     

Inheritance of shell colours in the noble scallop Chlamys nobilis (Bivalve: Pectinidae)

The noble scallop Chlamys nobilis is polymorphic in its shell colour, which includes orange, orange‐purple, purple and brown. In this study, the inheritance of shell colours of this species was investigated by analysing shell colour segregation in juvenile scallops produced from cross‐fertilization. Totally, twenty two families derived from four types of parental crosses were produced. The results clearly demonstrated that shell colour in this species was consistently inherited but insensitive to the environmental factors given that each family was maintained in a common environment. The pattern of the four superficial shell colours in C. nobilis appears to be genetically controlled by the interaction of one pair of nonallelic genes, with one locus showing dominance epistasis to the other one. One‐locus‐three‐allele model was proposed to explain the genetic relationship of the orange‐purple colour dominant to the purple and brown colours, and the purple colour dominant to the brown colour. While the phenotypic ratio of 12:3:1 detected in one specific family showed that the dominant allele of the other locus controlling orange colour may mask the effect of the locus controlling orange‐purple, purple and brown colours. The present results provide a genetic basis for selective breeding in the noble scallop in terms of shell colour.     

Pathogenic threats and probiotic use in larviculture of the scallop,Pecten maximus

During a series of experiments, bacteriological elements in scallop larval rearing were investigated: larvae susceptibility to pathogens as a function of their age, and the use of probiotic bacteria during larviculture. Younger larvae (d5 PF) were highly more susceptible to pathogenic‐challenge than their older siblings, which were challenged at an older age (d15 PF). A challenge with 10⁴ CFU mL^?1 of V. pectenicida killed 100% of d5 PF larvae 7 days following challenge, yet killed only 9% of d15 PF larvae 9 days following challenge. Use of the probiotics Phaeobacter gallaeciensis, Alteromonas macleodii 0444 and Neptunomonas sp. 0536, provided for larger larvae, a high yield of competent larvae and, perhaps more importantly, protection against pathogen‐challenge similar to levels achieved from antibiotic use. When challenged with V. pectenicida, d29 survivals were 20.3%, 85.1% and 75.0% respectively for control (no probiotic), antibiotic treated, and ‘probiotic mix’ administered larvae. Use of potential probiotic Pseudoalteromonas sp. D41 appeared to hinder scallop larvae. Future use of probiotics in scallop larval rearing would benefit from combined use of P. gallaeciensis, A. macleodii 0444 and Neptunomonas sp. 0536.