Possible cytotoxic effects of the dinoflagellate, Gyrodinium aureolum, on juvenile bivalve molluscs

Juveniles of eight commercially important species of bivalve molluscs (Spisula solidissima, Argopecten irradians, Crassostrea virginica, Mytilus edulis, Mya arenaria, Ostrea edulis, Mercenaria mercenaria, Placopecten magellanicus) were exposed in the laboratory to the commonly occurring dinoflagellate, Gyrodinium aureolum. Histological analyses of gut tissues indicated that the impact of G. aureolum on the shellfish was species-specific. High rates of mortality were noted in the bay scallop, A. irradians, but not in other molluscan species. There were no pathological differences between control animals and animals fed G. aureolum in S. solidissima, M. arenaria, or M. mercenaria. The most severely affected molluscs were C. virginica and A. irradians. C. virginica did not exhibit differences in digestive gland parameters between control and experimental animals; however, several animals did show significant mantle and gill lesions. Bay scallops exhibited decreased height of absorptive cells and increased lumen diameter after exposure to Gyrodinium suggesting, at least, poor food quality of Gyrodinium. Evidence of toxic effects was not identified in the digestive gland. Several bay scallops also showed variable amounts of inflammation in the kidney associated with protozoal infestations and variable amounts of predominately rod-shaped bacteria within the urinary space. Aquaculturists, especially of scallop species, should monitor for the presence of G. aureolum. Given its large size (25-30 m), G. aureolum could be filtered from incoming water to hatcheries, thus avoiding mass mortalities of spat and juvenile scallops.     

Connectivity of the bay scallop (Argopecten irradians) in Buzzards Bay,Massachusetts, U.S.A.

The harvest of bay scallops (Argopecten irradians) from Buzzards Bay, Massachusetts, U.S.A. undergoes large interannual fluctuations, varying by more than an order of magnitude in successive years. To investigate the extent to which these fluctuations may be due to yearly variations in the transport of scallop larvae from spawning areas to suitable juvenile habitat (settlement zones), a high‐resolution hydrodynamic model was used to drive an individual‐based model of scallop larval transport. Model results revealed that scallop spawning in Buzzards Bay occurs during a time when nearshore bay currents were principally directed up‐bay in response to a persistent southwesterly sea breeze. This nearshore flow results in the substantial transport of larvae from lower‐bay spawning areas to settlement zones further up‐bay. Averaged over the entire bay, the spawning‐to‐settlement zone connectivity exhibits little interannual variation. However, connectivities between individual spawning and settlement zones vary by up to an order of magnitude. The model results identified spawning areas that have the greatest probability of transporting larvae to juvenile habitat. Because managers may aim to increase scallop populations either locally or broadly, the high‐connectivity spawning areas were divided into: (i) high larval retention and relatively little larval transport to adjoining settlement areas, (ii) both significant larval retention and transport to more distant settlement areas, and (iii) little larval retention but significant transport to distant settlement areas.     

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.     

Bacteria in the culture of the scallop Argopecten purpuratus (Lamarck, 1819)

The scallop Argopecten purpuratus is one of themajor resources of commercial importance in Chilean aquaculture. One of themajor limiting factors for the culture of this species has been mass mortalityoccurring during production of juvenile seed organisms where massmortality of veliger larvae has been attributed to the presence of pathogenicbacteria in scallops and hatchery systems. Bacteriological studies havedemonstrated that in addition to bacterial pathogens, beneficial bacterialspecies capable of improving scallop larval survival may also be isolated fromscallops and hatchery systems. Research has been carried out on thedetermination of the feasibility of implementing beneficial bacteria in thecontrol of culture pathogens, thus reducing the need for chemotherapeuticmethods. The present review analyzes bacteriological research data on thedifferent roles of bacteria associated with scallop culture and discussesrecentdata on the implementation of beneficial bacteria in biological control ofpathogens in larval mass cultures of Argopectenpurpuratus.     

Induced triploidy in the bay scallop, Argopecten irradians, and its effects on growth and gametogenesis

Triploidy was induced in the bay scallop, Argopecten irradians, by treating newly fertilized eggs with cytochalasin B. Treatment for 20 min duration 10 min after fertilization resulted in 66% triploidy of scallops in the 0.05 mg/l cytochalasin treatment group and 94% triploidy of scallops in the 0.1 mg/l cytochalasin treatment group, detected by measuring the relative DNA content of scallop granulocytes using flow cytometry. Individually labelled scallops of known ploidy were grown in the Damariscotta River estuary in south-central Maine, U.S.A. from May 24 to September 15, 1982. Mean adductor muscle weight in triploid scallops was 73% greater than that of diploid controls and mean total body tissue wet weight was 36% greater. Shell inflation was significantly greater in triploids, while shell height and length were unaffected. The indexes of weight and glycogen content of the adductor muscle were significantly greater in triploids at the end of the growing season. The majority of triploid scallops failed to ripen during the summer months, while diploid scallops ripened and spawned.     

Utility of high-density plantings in bay scallop, Argopecten irradians irradians, restoration

Two different methods of establishing high-density spawner sanctuaries for bay scallop (Argopecten irradians irradians) restoration were evaluated over 2 years at a site in Northwest Harbor, East Hampton, New York, USA. Hatchery-reared scallops, which had been overwintered at nearby sites, were free-planted directly to the bottom in late March/early April at an initial target density of 94?C128 scallops/m². In addition, scallops were stocked in off-bottom culture units consisting of three vertically stacked 15-mm mesh ADPI^® bags at densities of 50, 100, or 200 scallops/bag (=117, 234, or 468 scallops/m²), respectively. Survival of scallops differed significantly by year, planting method, and scallop source. Survival of free-planted scallops was generally lower than caged scallops. Better survival of free-planted scallops in 2005 versus 2006 likely reflected the presence of luxuriant eelgrass beds in 2005, which were absent in 2006. Survival of scallops in ADPI bags was not appreciably related to stocking density. Shell growth was highest for free-planted scallops; in cages, growth was somewhat better at 50 versus 200 scallops/bag. Wet weights of epibionts were significantly higher in caged versus free-planted scallops. Reproductive condition of scallops stocked at 50/bag was usually higher than at 200/bag. Both free-planting and off-bottom systems yielded high densities of adult bay scallops at the time of spawning, which ensures a higher probability of successful fertilization of spawned eggs and thus a greater potential for success of restoration efforts.     

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.     

利用地下海水进行海湾扇贝越冬的效果研究

把5cm以上海湾扇贝亲贝按43-50个／m^3密度吊养于水泥沉淀池,利用附近井水调温：使池水温度达4℃以上。越冬两个半月,成活率84％以上,而自然海区越冬贝成活率仅70％．升温促熟后．亲贝产卵孵化率60％以上,而自然海区越冬贝仅为15．1％。地下海水越冬贝的单位水体出苗量为505万粒／m^3和544万粒／m^3,而自然海区越冬贝出苗量仅有209万粒／m^3．证明利用地下海水调温,在沉淀池进行海湾扇贝亲贝越冬,效果明显,完全可行．     

Scallop introductions and transfers, from an animal health point ofview

The effects of transfers and introductions of bivalue molluscs are alwaysmore or less unpredictable. Moving scallops, there is a risk of introducingpathogenic agents or of disturbing the balance between potentiallypathogenic agents and host species in the recipient ecosystem. Risk is noteliminated by merely following official regulations. Some factors which maybe important in order to assess risk, and to choose the level of risk we arewilling to accept, are: The existence of ``stowaways', and the action of mechanical vectors.One organism may carry another, and it is seems impossible to obtain a``clean' organism, in spite of long quarantines. The biological vector function. There may be unknown reservoirs,intermediate or alternative hosts of pathogenic agents in the ``new'environment. An introduced species may also carry potentially pathogenicagents into a new ecosystem. The often lacking knowledge concerning epizootiology. Life cycles ofmany pathogenic agents are poorly known, as are the infectious dose ofagent, influence of environmental factors on disease, etc. The diagnostic tools, and the ``human factor' in diagnostics. Methodsare often not sensitive enough to detect a pathogenic agent in a carrierstate, or immediately after the agent has entered the host, or at a lowprevalence/how intensity level. It is also important that personnel aresufficiently trained to do the diagnostic work. The official priority of disease control. There are no notifiablediseases of scallops. EC regulations, and the ``one area/one agent/one bivalve species'management. National and international trade, including illegal transport of livebivalves.Considering these factors enables a better focus on the riskfactors and the assessment of risks associated with introductions andtransfers of scallops. Consideration may also help to clarify the scientificlevel of knowledge and experience required to handle scallop diseases, andfocus on practical problems in scallop health control.     

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.     

The recruitment of scallops (and beyond) by two different artificial collectors (Gulf of Taranto,Mediterranean Sea)

This study provides for the first time an evaluation of the natural availability of scallop seeds along the coastal area of Taranto (Mediterranean Sea, Southern Italy). To select the best artificial collectors to harvest scallop seeds in this area, cylindrical collectors (Cyl) were compared to traditional ‘Japanese‐style onion bags’ (Bag) across three sites. Scallops represented 26.6% of total bivalve recruitment among all collectors (782 ± 331 ind. m^?2). The most recruited scallops were Flexopecten glaber and Mimachlamys varia. The white (F. glaber) and black scallops (M. varia) were abundant at all three sites, while the queen scallop, Aequipecten opercularis, was only found at one site. Beyond the recruitment of scallops, numerous other potential commercial bivalve species were collected, including Limaria tuberculata, which was the most abundant bivalve species (33.3% of total recruitment). At all sites, Bag collectors had higher recruitment than Cyl collectors. Scallops recruited in artificial collectors exhibited a multicohort size distribution at most sites, suggesting potentially continuous reproductive activity in the scallop populations. F. glaber, M. varia and L. tuberculata could be good candidates to diversify the aquaculture production because of the availability of seed and their growth rate. Moreover, the farming of these bivalves integrates well with other forms of aquaculture (e.g. mussels), thus potentially offering farmers an additional source of income.     

Genetic considerations in transfers and introductions of scallops

As the potential of scallop aquaculture becomes increasinglyrealised, transfers (movement within a species' range) andintroductions (movement outside a species' range) of scallops arebecoming more common. To predict the genetic consequences oftransfers, information on genetic differences between source andrecipient populations is vital. Morphological, allozyme and DNAbased data on genetic differentiation of scallop populations andscallop sub-species are presented and discussed. Otherconsiderations are the numbers of individuals transferred andwhether they are wild stock or hatchery product. Loss of geneticdiversity is difficult to avoid in hatchery conditions althoughthere are ecological advantages to using disease-free hatcheryseed. Mitochondrial DNA data indicating significant geneticconsequences of the introduction of Argopecten irradians fromthe USA to China are discussed and compared with data onPatinopecten yessoensis introduced from Japan to Canada.Potential risks and consequences of hybridisation should beexperimentally assessed before introductions of scallops arecarried out. Hybridisation is unpredictable and can lead to lossof genetic diversity or breakdown of co-adapted gene complexes.The use of sterile triploid scallops for introductions to avoid hybridisation and reduce ecological impact has merit butreversion to diploidy may occur.     

Some effects of gas-supersaturated seawater on Spisula solidissima and Argopecten irradians

Two size classes of the surf clam, Spisula solidissima, and the bay scallop, Argopecten irradians, were exposed to different concentrations of gas-supersaturated seawater in a flowing seawater system. Both species tested experienced no mortality when held in the control treatment maintained at 96% oxygen and 109% nitrogen. Mortality, gill tissue damage, gas emboli, membranous tissue blisters, and abnormal secretion of shell material were induced experimentally at elevated levels of gas supersaturation. Results indicate significant mortalities of surf clams and scallops held at 114% O₂ and 195% N₂, and at higher levels of gas concentration. These values suggest a point of reference for the bivalve culturist in identifying potential problems which can be caused by gas-supersaturated seawater.     

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).     

提高海湾扇贝虾池保苗成活率技术研究

利用６５亩虾池进行提高海湾扇贝保苗成活率技术研究，入池稚贝２．１亿粒，经４３天暂养，出池商品苗９７２０万粒，成活率达４６．３％，纯益３５．８４万元。而海上保苗成活率仅为１０％左右。１９９４年２月，专家鉴定认为，本研究居国内先进水平。     

Bivalve hatchery technology: The current situation for the Pacific oyster Crassostrea gigas and the scallop Pecten maximus in France

The French oyster farming industry relies almost exclusively on juveniles collected from the natural environment; the supply of spat produced by hatcheries is low, about 10 % of the industry's requirements. Development through selective breeding of oyster stocks which are better suited for aquaculture purposes, is likely to reverse this tendency since only hatcheries will be able to supply such animals. Scallop farming, which at present is poorly developed in France, relies exclusively on hatchery produced spat. Although hatchery technology is constantly being improved, significant production problems remain which must be solved before hatcheries become a major supplier of juveniles for the industry. This paper describes the present state of hatchery technology in France based on experimental results obtained with the great scallop Pecten maximus and the Pacific oyster Crassostrea gigas, over the past ten years. Compared to the great scallop, the Pacific oyster has higher D larva yields (60 % for C. gigas vs. 30 % for P. maximus) and a faster larval growth rate (10 μm·d⁻¹ for C. gigas vs. 5 μm·d⁻¹ for P. maximus). However, Pacific oysters have a greater heterogeneity during larval development and higher mortality rates (40 % for C. gigas vs. 25 % for P. maximus) which produce lower overall yields of pediveliger larvae ready-to-set for Pacific oysters (15 %) compared to the great scallop (30 %). Development of continuous larval and post-larval culture methods along with development of continuous phytoplankton technology offers one of the most promising methods to improve molluscan hatchery techniques.     

Growth and survival of the scallop Lyropecten (=Nodipecten) nodosus (L. 1758) in suspended culture in the Cariaco Gulf (Venezuela) during a non-upwelling period

Growth and survival of the scallop Lyropecten nodosus were studied in 1997 at two sites (inner and outer Turpialito Bay) during a non‐upwelling period normally occurring between August and November. Individuals had an initial shell height of 4.86 cm (SD=1.64 cm). Both experimental groups were held in suspended plastic baskets at the same depth (4 m). Measurements of shell height and dry weights of shell, gonad, digestive gland, remaining tissues and shell biofouling were taken at monthly intervals. Environmental parameters, including temperature, phytoplanktonic biomass, total particulate material (TPM) and associated organic (POM) and inorganic (PIM) fractions, were recorded simultaneously. At the end of the study, significant differences in growth and survival of scallops were observed between the two experimental sites. Scallops maintained inside the bay showed a 22% greater increase in shell height (7.41±0.27 cm) than those placed outside the bay (6.37±0.41 cm). Survival of scallops inside the bay was 31% higher compared with scallops outside. The greater availability of food of phytoplanktonic origin during the first two experimental months (July and August) together with greater POM throughout the whole experimental period except September, at the inner bay site, probably explained survival and growth differences observed between the two locations. Results suggest that, during the non‐upwelling period (characterized by low primary productivity and high water temperatures), POM of sedimentary origin may play an important role as an energy source required for metabolic and reproductive activities of L. nodosus.     

Bacteria associated with early life stages of the great scallop, <Emphasis Type="BoldItalic">Pecten maximus</Emphasis>: impact on larval survival

A bacteriological study was carried out at a scallop (Pecten maximus) hatchery near Bergen, western Norway following a severe increase in mortality rates during the larval stages of the scallops. No larvae survived to settling, except for those in groups treated prophylactically with chloramphenicol. In order to identify pathogenic strains of bacteria, we performed a challenge test on 10- to 16-day-old larvae using isolated bacterial strains from the hatchery. Infection with six of these strains produced mortalities that were not statistically different from that resulting from infection with the known pathogen Vibrio pectenicida. However, about 5% of the strains tested in the challenge experiment produced higher motility rates than found in the unchallenged control group, indicating a possible probiotic effect. On the basis of 16S rDNA analysis on these strains, the phylogenetic tree indicated two groups of apparent pathogens: (1) one strain, LT13, grouped together with Alteromonas/Pseudoalteromonas; (2) a cluster of strains grouped together with Vibrio splendidus (LT06, LT21, LT73, PMV18 and PMV19). Strain LT13 was isolated from cultures of the microalga Chaetoceros calcitrans used for feed, while the other strains were isolated from larval cultures. Transmission electron microscopy showed intracellular bacteria that resembled bacteria in the groups Chlamydiaceae and Rickettsiaceae.     

ALGAE AND DETRITAL MATTER AS FOOD FOR JUVENILE PURPLE-HINGE ROCK SCALLOPS,Hinnites multirugosus GALE

Feeding experiments using commonly-cultured algae were conducted with purple-hinge rock scallops, Hinnites multirugosus Gale, to suggest the application of these algae to hatchery culture of scallops. The uptake of finely divided particulate matter was also studied to ascertain the possible importance of detritus as a supplemental food for the rock scallop. A 1:1:1 mixture by culture volume of Tahitian Isochrysis, Tetraselmis suecica, and Dunaliella salina appeared to be superior as a diet for juvenile rock scallops. Significant growth also occurred in juvenile rock scallops fed T-Isochrysis, T. suecica, Isochrysis galbana, and Rhodomonas sp. Gymnodinium splendens, Monochrysis lutheri, and Dunaliella salina fed alone were poor foods for juvenile rock scallops. Finely divided particulate matter as radiolabeled abalone fecal matter was utilized as food. Significant radioactivity appeared in DNA, RNA, lipid, protein, carbohydrate, and free-reducing substances after one week providing evidence that particulate matter was incorporated into juvenile rock scallop metabolic pathways.     

Suspension-feeding aquaculture systems: Effects of phytoplankton concentration and temperature on growth of the bay scallop

The growth rate of the bay scallop Argopecten irradians was studied in relation to temperature and phytoplankton concentration. Results suggest that normal variations in phytoplankton concentration do not influence the growth rate of scallops in their natural habitat. Increasing the concentration of phytoplankton above natural levels did not result in increased growth rates while decreasing the phytoplankton concentration resulted in a decrease in growth rate of the scallops. Under extremely low phytoplankton concentrations, such as those that characterize ‘clean water’ effluent from a culture system, the animals ceased growing. A mathematical model of scallop growth rate as a function of phytoplankton concentration is proposed as a tool for comparing the functioning of different suspension feeders in aquaculture systems.