Placopecten Magellanicus Research Articles

Developing a bioeconomic framework for scallop culture optimization and product development

Aquaculture is the fastest growing food production sector in the world and is quickly diversifying. In the Northwest Atlantic, interest in sea scallop (Placopecten magellanicus) (hereafter scallop) aquaculture has grown substantially. However, technical and economic challenges have hindered industry growth. We conducted bioeconomic simulations for various sized farms that targeted either live “whole” scallops or the shucked adductor muscle “meat.” The majority of farms selling whole scallops were profitable. However, all farms selling meats generated negative returns. Labor made up the greatest portion of costs in model simulations and increased linearly with farm size, representing a significant bottleneck. Whole scallop farm value was most sensitive to changes in (1) market price and (2) time to market. Our analysis suggests four strategies to increase farmed scallop production in the Northwest Atlantic: (1) mechanize low density net culture, (2) optimize net stocking densities, (3) build site selection tools, and (4) invest in consumer education, end-markets, and biotoxin testing for whole scallops. The sector will require a combination of regulatory, industry, and research cooperation to overcome these pressing challenges, but holds the potential to profitably diversify the bivalve aquaculture industry.

Dietary Phospholipids Prepared From Scallop Internal Organs Attenuate the Serum and Liver Cholesterol Contents by Enhancing the Expression of Cholesterol Hydroxylase in the Liver of Mice.

In this study, we successfully prepared scallop oil (SCO), which contains high levels of phospholipids (PL) and eicosapentaenoic acid (EPA), from the internal organs of the Japanese giant scallop (Patinopecten yessoensis), one of the most important underutilized fishery resources in Japan. The intake of SCO lowers the serum and liver cholesterol contents in mice; however, whether the fatty acids (FA) composition or PL of SCO exhibits any cholesterol-lowering effect remains unknown. To elucidate whether the cholesterol-lowering function is due to FA composition or PL of SCO, and investigate the cholesterol-lowering mechanism by SCO, in the present study, mice were fed SCO's PL fraction (SCO-PL), triglyceride (TG)-type oil with almost the same FA composition as SCO-PL, called SCO's TG fraction (SCO-TG), soybean oil (SOY-TG), and soybean's PL fraction (SOY-PL). Male C57BL/6J mice (5-week-old) were fed high-fat and cholesterol diets containing 3% (w/w) experimental oils (SOY-TG, SOY-PL, SCO-TG, and SCO-PL) for 28 days. The SCO-PL diet significantly decreased the serum and liver cholesterol contents compared with the SOY-TG diet, but the intake of SOY-PL and SCO-TG did not show this effect. This result indicated that the serum and liver cholesterol-lowering effect observed in the SCO intake group was due to the effect of SCO-PL. The cholesterol-lowering effect of SCO-PL was in part related to the promotion of liver cholesterol 7α-hydroxylase (CYP7A1) expression, which is the rate-limiting enzyme for bile acid synthesis. In contrast, the expression levels of the ileum farnesoid X receptor (Fxr) and fibroblast growth factor 15 (Fgf15), which inhibit the expression of liver CYP7A1, were significantly reduced in the SCO-PL group than the SOY-TG group. From these results, the increase in the liver CYP7A1 expression by dietary SCO-PL was in part through the reduction of the ileum Fxr/Fgf15 regulatory pathway. Therefore, this study showed that SCO-PL may be a health-promoting component as it lowers the serum and liver cholesterol contents by increasing the liver CYP7A1 expression, which is not seen in SOY-PL and SCO-TG.

A case report and statewide surveillance of “weak meat” condition of Alaska weathervane scallops, Patinopecten caurinus, linked to a recently identified pathogenic parasite, Merocystis kathae (Apicomplexa: Aggregatidae)

Weathervane scallop, Patinopecten caurinus, the largest scallop species in the world, is distributed from northern California, U.S.A., to the Bering Sea, and is only commercially harvested in Alaska. The fishery is considered well managed by the State of Alaska (U.S.A) Department of Fish and Game (ADF&G) and federal government, with many precautionary measures in place to avoid overharvest. There have been episodic declines in some management areas due to unknown causes. Fishermen also encounter scallops with abnormal adductor muscles, a condition colloquially termed “weak meat”, characterized by the retention of muscle when shucked, an obvious darkened discoloration, and/or an abnormal texture making the product unacceptable for marketing. A similar syndrome in Atlantic sea scallops, Placopecten magellanicus, described as “gray meat”, occurs in the eastern U.S. and Canada, and proposed causes include senescence, loss of bioenergetics due to chronic infestations, or a synergism of these factors. Recently a severe apicomplexan infection was found to cause a gray meat condition in Iceland scallops, Chlamys islandica, and the collapse of that stock. This parasite was subsequently detected in Atlantic sea scallops with the gray meat condition off the U.S. East Coast. Studies that followed identified the parasite as Merocystis kathae, previously described from the common whelk, Buccinum undatum, more than 100 years ago. In 2015 Bering Sea fishermen reported weak meat in their catch, so samples were submitted to ADF&G for diagnosis. Adductor muscles from all affected scallops had many large foci of an apicomplexan associated with necrosis, fibrosis, and muscular atrophy. Given the reduced quality, marketability, and possibly fitness of affected scallops, we performed a survey to estimate prevalence, intensity, and geographic distribution of this apicomplexan in Alaskan weathervane scallops. We sampled 180 scallops, from individual beds within each of the three major geographically broad scallop areas in Alaska. Overall prevalence was about 82%, ranging from 69 to 100% by district. Overall mean infection intensity, based on the number of parasite foci/section, was about 9 (range of 5–29, by location), with scallops from the Bering Sea and Southwest Kodiak being most severely infected. Molecular analyses confirmed that the Alaskan parasite is M. kathae, i.e., the same apicomplexan that caused the collapse of Icelandic scallops and a suspected cause for gray meat and mass mortality of Atlantic sea scallops in northeast North America.

Meta-analysis of growth and mortality rates of net cultured sea scallops across the Northwest Atlantic

Scallops are one of the most heavily traded and widely consumed seafood in the world and the vast majority of production comes from aquaculture. In 2018, the global value of scallop aquaculture was over $5.8 billion USD with farms producing nearly three times the biomass as the entirety of the wild harvest. North American (specifically U.S. and Canadian) scallop aquaculture lags far behind the rest of the world. The U.S. is home to a valuable Atlantic sea scallop (Placopecten magellanicus) fishery. Yet demand for scallops far outstrips supply and the U.S. imports an almost equal amount, by value, of farmed scallop products. To capitalize on this trade imbalance, U.S. and Canadian aquaculturists have been developing a farmed sea scallop (hereafter scallop) industry, employing the Japanese practices of suspended net culture and the sale of whole and “roe-on” products. We examined the combined effects of culture method and environment on scallop shell growth and mortality. We compiled all published net cultured scallop shell growth and mortality rates recorded in the last 45 years in the Northwest Atlantic. Using generalized additive models (GAMs), we identified significant nonlinear interactions between growth, mortality, environmental conditions, and culture methods applicable from Maine, USA to Newfoundland, Canada. Optimum shell growth occurs within a temperature window of 10–15 °C. Growth is higher in pearl nets than in lantern nets, and is also highly sensitive to stocking density, which has large implications for farm sizes and thinning practices. Maximum mortality occurs at the highest temperatures in our dataset (~17 °C), while stocking density is only a significant predictor of product loss at high densities. Scallops are also more susceptible to mortality at shell heights under 25 mm. Both mortality rates and shell height growth rates were lower in the late spring and early summer after accounting for temperature effects. Careful temperature based site selection and proactive low density stocking can mitigate the effects of intraspecific competition and reduce handling related mortality. Identifying lease sites that provide both optimal environmental conditions and adequate space for low density net culture will be an important step in expanding scallop aquaculture in the Northwest Atlantic.

Size selectivity of the scallop fishery in the southern Gulf of St. Lawrence: Effects of ring size and washer type

In the southern Gulf of St. Lawrence (sGSL), there is a mostly supplementary fishery for sea scallops (Placopecten magellanicus) concentrated on three primary scallop beds in the Northumberland Strait. The fishery is not subject to an enforced minimum size limit and small scallops (<90 mm shell height) are often removed from this population before they have had time to adequately contribute to population recruitment, resulting in sub-optimal fishery yields and a partially size-suppressed population. This study aimed to provide stakeholders with information related to gear configuration changes that could potentially reduce catches of small scallops in the sGSL fishery by quantifying size-selectivity of different ring sizes (82.6 mm and 88.9 mm) and washer types (rubber and steel). We also compared the catches of small, fecund scallops (45–90 mm) across the different gear configurations. The gears with 82.6 mm rings had high retention of small scallops, with lengths of 50 % retention estimated to be 72.8 and 76.0 mm with rubber and steel washers, respectively. This increased to 87.9 mm and 95.5 mm, respectively, in the gears with 88.9 mm rings. It was estimated that with rubber washers, increasing ring size from 82.6 mm to 88.9 mm will reduce catch of small fecund scallops by 51 %, while reducing catch of large scallops by 27 %. Increasing ring size was more effective than changing washer type at increasing size selectivity of the gear. Previous research on scallop life history suggests that this reduction of large scallops will be temporary because the larger gear will ultimately shift the population size distribution towards larger scallops resulting in higher yield-per-recruit. These results will be useful to resource managers and stakeholders for stock assessments, and for future gear type decisions.

A switch in species dominance of a recovering pelagic ecosystem

Although many marine ecosystems have been adversely impacted by human activities,1 some are now recovering due to reductions in fishing pressure.2-4 Here, we document the recovery of an ecosystem subjected to intense anthropogenic activity for over 200 years, the Clyde Sea.5 This region once had productive fisheries for herring (Clupea harengus) and other fish, but these disappeared at the turn of the century.6,7 Using acoustic surveys of the pelagic ecosystem, we found that the Clyde Sea supports 100 times as many forage fish as in the late 1980s. However, herring has now been replaced by sprat (Sprattus sprattus), despite virtually no fishing on herring for 20 years. A combination of a warming sea,6 bycatch of herring in the prawn (Nephrops norvegicus) fishery,8,9 and susceptibility of herring to poor recruitment may have contributed to this unexpected recovery. We compare this to similar unexpected "recoveries" involving unforeseen ecosystem effects, such as the return of hake (Merluccius merluccius) to the North Sea;10,11 the recent expansion of the pelagic squat lobster, "munida," (Pleuroncodes monodon) off Peru;12 and the increase in scallop (Placopecten magellanicus) numbers on Georges Bank.13 The lack of a current sprat fishery in the Clyde presents a unique opportunity to develop an alternative industry for its seafaring community: ecotourism. Charismatic megafauna (whales, dolphins, and seabirds) that people will pay to see14 will, in time-if not already15,16-be drawn in by the abundance of forage fish now present, further restoring the biodiversity of the region after centuries of overexploitation.

Scallop dredge design using computational fluid dynamics and flume tank testing and the application of both methods to improving a low profile dredge

The Atlantic sea scallop (Placopecten magellanicus) is the focus of one of the most valuable fisheries on the east coast of the United States, but the incidental bycatch of flounder species could have negative impacts on the long-term sustainability of the scallop fishery. The low profile dredge (LPD) was conceived as a modified dredge that would reduce flounder bycatch by decreasing the vertical distance to the top of the dredge, allowing the fish to more easily swim over the top to escape. During initial development, two prototypes were tested at sea, and each reduced flounder catch with minimal reductions in scallop catch. To make continued refinement of the LPD more efficient and cost effective, we incorporated computational fluid dynamics (CFD) analysis and flume tank testing into our design strategy. The use of CFD analysis was validated with comparisons to flume tank tests and data from at-sea trials through examination of turbulent flow patterns and particle trajectories. There was a strong correspondence between the CFD simulation outputs and the results of the flume tank tests and at-sea gear trials, supporting the use of computer simulations during the early stages of gear design to speed up and reduce the cost of new gear development.

Impact of larval behaviors on dispersal and connectivity of sea scallop larvae over the northeast U.S. shelf

Sea scallops (Placopecten magellanicus) are a highly fecund species that supports one of the most commercially valuable fisheries in the northeast U.S. continental shelf region. Scallop landings exhibit significant interannual variability, with abundances widely varied due to a combination of anthropogenic and natural factors. By coupling a pelagic-stage Individual-Based scallop population dynamics Model (hereafter referred to as Scallop-IBM) with the Northeast Coastal Ocean Forecast System (NECOFS) and considering the persistent aggregations over Georges Bank (GB)/Great South Channel (GSC) as source beds, we have examined the dispersion and settlement of scallop larvae over 1978–2016. The results demonstrated that the significant interannual variability of larval dispersal was driven by biophysical interactions associated with scallop larval swimming behaviors in their early stages. The duration, frequency, and stimulus of larval vertical migration in the ocean mixed layer (OML) affected the residence time of larvae in the water column over GB. It thus sustained the persistent aggregations of scallops in the GB/GSC and Southern New England region. In addition to larval behavior in the OML, the larval transport to the Middle Atlantic Bight (MAB) was also closely related to the intensity and duration of northeasterly wind in autumn. There was no conspicuous connectivity of scallop larvae between GB/GSC and MAB in the past 39 years except in the autumn of 2009. In 2009, the significant larval transport to the MAB was produced by unusually strong northeasterly winds. Ignoring larval behavior in the OML could overestimate the scallop population’s connectivity between GB and the MAB and thus provide an unrealistic prediction of scallop larval recruitment in the region. Both satellite-derived SST and NECOFS show that the northeast U.S. shelf experienced climate change-induced warming. The extreme warming at the shelfbreak off GB tends to intensify the cross-isobath water temperature gradient and enhance the clockwise subtidal gyre over GB. This change can increase the larval retention rate over GB/GSC, facilitating enhanced productivity on GB.

Determining Discard Mortality of Monkfish in a Sea Scallop Dredge Fishery

AbstractDiscard mortality studies are considered a primary research priority, particularly for species and fisheries where discard rates are high. Monkfish (the commercial name for Goosefish) Lophius americanus supports the most lucrative finfish fishery in New England, and it is also the second highest bycatch species by weight in the sea scallop dredge fishery. Despite its commercial importance, no data exist with respect to monkfish discard mortality estimates for any gear type. The goals of this study were to evaluate the discard mortality process for monkfish captured in sea scallop dredge gear, estimate mortality rate, and develop best handling/management practices to mitigate the impact of monkfish bycatch in the sea scallop dredge fishery. Discard mortality was estimated during a field study conducted between June and October 2017 on board sea scallop commercial fishing vessels on Georges Bank in the Northwest Atlantic. Pop‐up satellite tags were affixed to 60 monkfish to track survival from 14 to 28 d postcapture. From these monitored individuals, high predation rates were observed (n = 18 out of 26 mortalities), and the bulk of mortalities (n = 21) occurred within the first 24 h of discarding. However, in light of having no clear method for disentangling capture‐related and tag‐induced predation, predation was noted exclusively as one or the other to account for uncertainty and provide an upper and lower bound of mortality. This approach suggested that the discard mortality rate was between 17.9% and 54.1% for monkfish discarded by scallop dredges and that elevated air temperatures (above thermal preferences) may contribute to increased mortality. Based on these results, it appears that monkfish discard mortality is lower than previous assumptions of 100%, and potential best‐practice management suggestions moving forward may include minimizing fishing in areas of high monkfish abundance or scheduling rotating time/area closures during periods when air temperature exceeds monkfish thermal tolerance of 13°C.

The coupled effects of stocking density and temperature on Sea Scallop (Placopecten magellanicus) growth in suspended culture

Despite the profitability of the wild Atlantic Sea Scallop, Placopecten magellanicus, fishery, the U.S. still imports more than 26,000 tonnes of various scallop products annually. Atlantic Sea Scallop (hereafter referred to as scallop) aquaculture is one method of mitigating this imbalance. We examined scallop growth at three sites across the mouth of Penobscot Bay, Maine to determine the coupled effects of lantern net stocking density and temperature on growth and mortality. Scallops were held in high and low (20 and 10 individuals tier−1, respectively) density treatments, and shell height measurements were recorded monthly for one year. We divided the growth rate analysis into three periods: winter - spring, summer, and fall. During summer across all sites, growth rates were 75 % higher in low-density nets than in high-density nets. We observed significant nonlinear relationships between shell height growth rate, temperature, and stocking density. Optimal growth occurred within a window of 10–15 °C. Above this threshold, there was a distinct negative relationship between temperature and growth. Our results highlight the importance of maintaining low densities within nets, particularly during periods of high temperature and growth. However, handling in summer and early fall may lead to mortality. Therefore, we recommend that growers stock nets at low densities in the spring, ensuring that they will not require thinning during peak temperatures. Similarly, finding sites that maximize time within a thermal envelope of 10–15 °C will be critical, which in the case of the Gulf of Maine will most likely warrant leasing sites at the mouths of estuaries and bays. These locations offer a combination of sufficient depth and space for sparsely stocked nets, adequate food levels, and optimal salinity and temperature.

Francisellosis of Yesso scallops Mizuhopecten yessoensis in Japan is caused by a novel type of Francisella halioticida.

Francisella halioticida, the causative agent of francisellosis of the giant abalone Haliotis gigantea, has also been isolated from Yesso scallops Mizuhopecten yessoensis, which presented with orange/pinkish lesions in the adductor muscle and experienced high mortality. However, it is not clear whether the F. halioticida isolated from the giant abalone and Yesso scallops are phenotypically and genetically identical to each other. The present study revealed that isolates from the giant abalone and Yesso scallops were phenotypically different, with slower growth in modified eugon broth and a lack of prolyl aminopeptidase and phenylalanine aminopeptidase in Yesso scallop isolates. Additionally, we found that 3 of 8 housekeeping genes were different between them. Based on these phenotypic and genetic differences, we propose that F. halioticida isolated from Yesso scallops in Japan be designated as the 'J-scallop type' to distinguish it from strains from abalone ('abalone type'). Whole-genome sequencing analysis of a strain belonging to the J-scallop type showed that the overall similarity between the J-scallop and abalone type strains was estimated to be 99.84%. In accordance with a lack of prolyl aminopeptidase activity, in general, all of the J-scallop type strains examined have a 1 bp deletion in the responsible gene encoding prolyl aminopeptidase. This deletion was confirmed in all F. halioticida in diseased Yesso scallops examined, suggesting that in Japan, francisellosis of Yesso scallops is caused by a novel type of F. halioticida and not by the abalone type.

Sensitivity to oil dispersants: Effects on the valve movements of the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus, in sub-arctic conditions.

In response to accidental oil spills at sea, chemical oil dispersants are utilized to limit negative impacts on nearby littoral zones. However, current evidence suggests that such dispersants may be toxic to aquatic organisms. Blue mussels (Mytilus edulis) and giant scallops (Placopecten magellanicus) were exposed to different environmentally relevant concentrations of oil dispersant and their behavioural responses were closely monitored using high frequency (10Hz) valvometry. Behavioural valve responses included rapid closures when oil dispersant was added to the experimental tanks. At higher concentrations, the mussels remained closed throughout the exposure period. The giant scallop displayed escape behaviours (clapping) prior to mortality, suggesting toxicity of the oil dispersant. Relationships between different behavioural indicators and oil dispersant concentrations were observed for both species, but with different trends. While scallops demonstrated positive correlations between gaping behaviours and dispersant concentration, mussels exhibited a concentration threshold beyond which the gaping behaviour was characteristic of longer closure periods. This study highlights behavioural response differences consistent with bivalve-specific biological traits: the continuous valve closure of an intertidal species, M. edulis, firmly attached to the substrate, and the escapement behaviours of a semi-mobile subtidal species, P. magellanicus. From these observations, it appears that valvometry could be used as a tool for environmental assessments.

Structure-dependent absorption of atypical sphingoid long-chain bases from digestive tract into lymph

BackgroundDietary sphingolipids have various biofunctions, including skin barrier improvement and anti-inflammatory and anti-carcinoma properties. Long-chain bases (LCBs), the essential backbones of sphingolipids, are expected to be important for these bioactivities, and they vary structurally between species. Given these findings, however, the absorption dynamics of each LCB remain unclear.MethodsIn this study, five structurally different LCBs were prepared from glucosylceramides (GlcCers) with LCB 18:2(4E,8Z);2OH and LCB 18:2(4E,8E);2OH moieties derived from konjac tuber (Amorphophallus konjac), from GlcCers with an LCB 18(9Me):2(4E,8E);2OH moiety derived from Tamogi mushroom (Pleurotus cornucopiae var. citrinopileatus), and from ceramide 2-aminoethyphosphonate with LCB 18:3(4E,8E,10E);2OH moiety and LCB 18(9Me):3(4E,8E,10E);2OH moiety derived from giant scallop (Mizuhopecten yessoensis), and their absorption percentages and metabolite levels were analyzed using a lymph-duct-cannulated rat model via liquid chromatography tandem mass spectrometry (LC/MS/MS) with a multistage fragmentation method.ResultsThe five orally administered LCBs were absorbed and detected in chyle (lipid-containing lymph) as LCBs and several metabolites including ceramides, hexosylceramides, and sphingomyelins. The absorption percentages of LCBs were 0.10–1.17%, depending on their structure. The absorption percentage of LCB 18:2(4E,8Z);2OH was the highest (1.17%), whereas that of LCB 18:3(4E,8E,10E);2OH was the lowest (0.10%). The amount of sphingomyelin with an LCB 18:2(4E,8Z);2OH moiety in chyle was particularly higher than sphingomyelins with other LCB moieties.ConclusionsStructural differences among LCBs, particularly geometric isomerism at the C8–C9 position, significantly affected the absorption percentages and ratio of metabolites. This is the first report to elucidate that the absorption and metabolism of sphingolipids are dependent on their LCB structure. These results could be used to develop functional foods that are more readily absorbed.

The Effects of Scallop Dredge Fishing Practices on Physical, Behavioral, and Physiological Stress in Discarded Yellowtail Flounder, Windowpane, and Fourspot Flounder

AbstractThe Atlantic sea scallop Placopecten magellanicus dredge fishery is one of the most lucrative commercial fishing industries in the northeastern United States, and fish bycatch can comprise up to ~42% of the total catch. Benthic species, such as flatfish, are particularly susceptible to unintended capture in scallop dredge gear, and mitigating bycatch and associated mortality has been mandated a priority for fisheries management. Based on this management need, the present study evaluated the physical, physiological, and behavioral stress responses of Yellowtail Flounder Limanda ferruginea, Windowpane Scophthalmus aquosus, and Fourspot Flounder Paralichthys oblongus to capture in the scallop dredge fishery. More specifically, we used generalized additive models and linear regression models to assess the influence of various fishing practices, environmental conditions, and biological factors on injury condition, physiological parameters, and reflex indicators. Although these flatfish species appeared to be physically resilient to capture based on an observable injury assessment, dredge capture and handling factors proved stressful, with the degree of immediate mortality, physiological disturbances, and reflex impairment varying by species. While multiple factors influenced the degree of stress in these species, based on our results the reduction of tow duration and limiting air exposure/sorting duration would likely be the most effective strategies to mitigate the impact of scallop dredge fishing on these flatfish species.

Predictive Models of Yellowtail Flounder Bycatch in the U.S. Sea Scallop Fishery on Georges Bank

Predictive Models of Yellowtail Flounder Bycatch in the U.S. Sea Scallop Fishery on Georges Bank

Comparison of the Cholesterol-Lowering Effect of Scallop Oil Prepared from the Internal Organs of the Japanese Giant Scallop (Patinopecten yessoensis), Fish Oil, and Krill Oil in Obese Type II Diabetic KK-A y Mice.

Due to the growing demand of n-3 polyunsaturated fatty acids (PUFA) as supplements and pharmaceutical products worldwide, there are concerns about the exhaustion of n-3 PUFA supply sources. We have successfully prepared high-quality scallop oil (SCO), containing high eicosapentaenoic acid and phospholipids contents, from the internal organs of the Japanese giant scallop (Patinopecten yessoensis), which is the largest unutilized marine resource in Japan. This study compared the cholesterol-lowering effect of SCO with fish oil (menhaden oil, MO) and krill oil (KO) in obese type II diabetic KK-A y mice. Four-week-old male KK-A y mice were divided into four groups; the control group was fed the AIN93G-modified high-fat (3 wt% soybean oil + 17 wt% lard) diet, and the other three groups (SCO, MO, and KO groups) were fed a high-fat diet, in which 7 wt% of the lard in the control diet was replaced with SCO, MO, or KO, respectively. After the mice were fed the experimental diet for 42 days, their serum, liver, and fecal lipid contents as well as their liver mRNA expression levels were evaluated. The SCO group had significantly decreased cholesterol levels in the serum and liver; this decrease was not observed in the MO and KO groups. The cholesterol-lowering effect of SCO was partly mediated by the enhancement of fecal total sterol excretion and expression of liver cholesterol 7α-hydroxylase, a rate-limiting enzyme for bile acid synthesis. These results indicate that dietary SCO exhibits serum and liver cholesterol-lowering effects that are not found in dietary MO and KO and can help prevent lifestyle-related diseases.

Using satellite remote sensing to improve the prediction of scallop condition in their natural environment: Case study for Georges Bank, Canada

The continuous, synoptical and high spatio-temporal resolution of thermal and visible satellite observations constitute an asset when characterizing and monitoring biogeochemical cycles in the oceans. In particular, they provide a unique insight into the hydrodynamics of the surface ocean and phytoplankton phenology. This information can be combined with in-situ observations of higher trophic levels to understand the functioning of the marine ecosystem, with potential use for fisheries and aquaculture. In the Gulf of Maine, off the eastern seaboard of North America, Georges Bank is one of the world's most productive natural sea scallop (Placopecten magellanicus) fisheries, which sustains economically valuable fisheries in Canada and the US. In Canada, the relationship between the scallop meat weight and its shell height (known as scallop condition) is used to obtain biomass estimates for stock assessment and thereby influences the fishing quotas. On Georges Bank, for a 100 mm shell height scallop, scallop condition has varied significantly interannually between 10.2 g and 19.5 g. Establishing a relationship between environmental factors and scallop condition would improve the forecasting of scallop biomass and reduce the uncertainty when determining the total allowable catch for the subsequent fishing season. In this study, satellite remote-sensed sea-surface temperature (SST) and chlorophyll-a concentration (Chla) coupled with in-situ measurements of scallop condition (SC) on Georges Bank were used to assess the relationship between SC and satellite-derived environmental conditions between 1985 and 2019 for SST and between 1998 and 2019 for Chla. The inter-annual variation of SC in May was found to be positively correlated (p-value <0.001) with the variation in SST in winter-spring months of the current and previous year of the SC survey. An empirical linear model for the estimation of SC was developed and validated using two independent datasets of satellite SST (r2 = 0.64, MAPD = 7%). Another model using cumulative SST in the previous year only was also provided (r2 = 0.58, MAPD = 7.7%), which could serve as an alternative choice when the SST products in the current year are not yet available for use. There was a weak relationship observed between SC and Chla; this is likely due to the influence of water-column vertical mixing on transport of phytoplankton to the benthic zone where the sea scallop resides. Our study indicates that a cost-effective satellite-derived SST product can be used to improve predictions of SC and provide useful information and decision support tools for managing scallop stocks.

Size and Age Characteristics and Phenotypic Peculiarities of Somatic Growth of the Black Sea Mollusk Flexopecten glaber ponticus (Bivalvia, Pectinidae)

This paper presents a preliminary analysis of the morphological, physiological, and biochemical parameters of somatic growth in the Black Sea scallop, Flexopecten glaber ponticus Bucguoy, Dautzenberg et Dollfus 1889, from a coastal site near Sevastopol, Crimea. The species is one of the few marine Black Sea mollusks listed in the Red Book of Sevastopol and Crimea with the status “Diminishing in numbers.” The peculiarities of soft tissue somatic growth have been studied in three size groups differing in linear diameter: 13–17, 21–24, and 25–30 mm. An analysis of the total RNA in tissue homogenates has shown that the rate of protein synthesis in the first and second groups (under-yearlings) is 1.2–1.5 times higher compared to adults. The population reveals seven color morphs (phenotypes). Three phenotypes (beige, violet, and gray-and-brown) are characterized by high-level protein synthesis. Mollusks of a mixed “multi” phenotype have the lowest level of tissue biosynthesis, usually being 2.5 times lower than that for other morphs. The results obtained indicate that the growth processes are linked to the color of the mollusk shell. High direct correlations between the weights of the total wet mass and the tissue mass observed in all mollusk groups may be evidence of positive growth allometry.

Not only greening: The effects of marennine produced by Haslea ostrearia on physiological traits of three bivalve species

The marine diatom Haslea ostrearia is known for its ability to produce marennine, a blue-green water-soluble pigment, which is responsible for the oyster greening phenomenon in the French Atlantic Coast. Marennine can be considered a bioactive extracellular compound (BEC) as it exhibits activities against detrimental pathogens in bivalve aquaculture. However, marennine could also be toxic to animals. The aim of this experimental study was to assess the effect of marennine produced by H. ostrearia upon three commercially important bivalve species, the American oyster Crassostrea virginica, the blue mussel Mytilus edulis and the giant scallop Placopecten magellanicus. Effect of this BEC was also assessed on different ontogenic stages of scallops. The animals were exposed to 3 mg L−1 of marennine and physiological response associated with clearance rates (CR), oxygen consumption and condition index (CI) were measured after 16 h of exposure (day 0), and after one subsequent week of recovery (day 7). In the short term, CR and oxygen consumption on mussels and oysters were significantly altered by marennine but not for scallops. CR recovery was observed in oysters after seven days, but no depuration was observed in mussels. Nevertheless, oxygen consumption in both mussels and oysters recovered on day 7. CI in the marennine-exposed group for both adult oysters and scallops was not significantly different, yet CI of mussels was lowered by 18.2 % compared to control. Scallop adults seemed largely resistant to marennine, but juveniles were more susceptible with a reduced CR and oxygen consumption by 71.9 % and 24.5 %, respectively, and no depuration activity observed until day 7. Additionally, CI in marennine-exposed juvenile scallops was 27 % lower than that of control. This study demonstrates species- and age-specific effect of marennine on bivalves, thus highlighting the importance of further assessment on the utilization of this pigment as a natural product decreasing pathogenicity of bacteria in shellfish aquaculture systems.

Effects of dietary oils prepared from the internal organs of the Japanese giant scallop (Patinopecten yessoensis) on cholesterol metabolism in obese type-II diabetic KK-Ay mice.

Our research team has successfully prepared high‐quality scallop oil (SCO), containing high eicosapentaenoic acid (EPA) and phospholipids (PL) from the internal organs of Japanese giant scallop (Patinopecten yessoensis) which is the largest unutilized marine resource in Japan. In this study, we prepared SCOs from scallop internal organs obtained from Mutsu (Aomori) and Uchiura (Hokkaido) bays in Japan, and named them SCO‐M and SCO‐U, respectively. This study aimed to investigate the effects of dietary SCO‐M and SCO‐U on cholesterol metabolism in obese type‐II diabetic KK‐Ay mice. Four‐week‐old male KK‐Ay mice were divided into four groups. The Control group was fed with AIN93G‐modified high‐fat (3 wt% soybean oil + 17 wt% lard) diet, and the other groups were fed with high‐fat diet, in which 7 wt% of the lard contained in the Control diet was replaced with SCO‐M, SCO‐U, or tuna oil (TO). After the mice had been fed with the experimental diet for 49 days, their serum, liver, and fecal lipid contents, as well as their liver messenger ribonucleic acid expression levels, were evaluated. The SCO‐M and SCO‐U groups were significantly decreased liver cholesterol contents compared to those of the Control and TO groups, partially through the enhancement of the fecal neutral sterol excretions and the tendency to increase the cholesterol 7α‐hydroxylase expression level of the liver. These results indicated that dietary SCO‐M and SCO‐U exhibited cholesterol‐lowering functions in the liver that can help prevent the development of lifestyle‐related diseases.