To develop selection programs for the great scallop, artificial reproduction of the species needs to be improved by gamete cryobanking. Here, a set of four experiments was designed in order to define the basic elements of a cryopreservation protocol for scallop sperm, including extender composition (experiment 1), cryoprotectant selection (2), cooling rate (3), and assessment of the effects of sperm cryopreservation on sperm motility and fertilization capacity (4). Sperm was collected after serotonin injection (100 μl of a 10-mM solution) and frozen in 500-μl straws. For the first three experiments, the percentage of motile fresh sperm (80 ± 4%, mean ± SEM) was significantly higher than that observed for thawed sperm (11 ± 2%). During the first experiment, no significant difference of the percentage of motile thawed sperm was observed among the three saline extenders tested: seawater, calcium-free Hanks’ balanced salt solution (Ca-free HBSS) and DCSB4 solution. However, a complementary experiment (2) showed that a significantly higher percentage of motile thawed sperm was recorded using DCSB4 than with Ca-free HBSS as an extender. During the third experiment, sperm motility was higher when using polyethylene glycol (10% PEG) as a cryoprotectant, than when using dimethyl sulphoxide, DMSO (10 and 20%), methanol (10%) and ethylene glycol (10% EG). A higher D-larval rate was obtained during the fourth experiment, using fresh sperm than thawed sperm, and using a 500:1 sperm-to-egg ratio compared with a 50:1 ratio. There is some evidence of inter-individual variations in sperm tolerance to cryopreservation. In conclusion, the highest survival of great scallop sperm after thawing was recorded using the following conditions: DCSB4 extender (1:3 vol/vol sperm to extender dilution), PEG cryoprotectant (10%) and straws maintained at 5.5 cm above liquid nitrogen.

The aim of this project was to evaluate the impact of probiotic (Phaeobacter gallaeciensis, X34 strain) treatment on the complete development (from veliger to metamorphosis) of Pecten maximus larvae in the context of a bacterial challenge and in conditions more representative of hatchery practices. To that effect, the present study was divided into two main steps. In the first, we used in vitro analyses (antibiograms and microplate assays) to validate the inhibition abilities of X34 on the growth of four Vibrio pathogen species. During the second step, we added pathogens (Vibrio pectenicida) into rearing tanks after two weeks of pre-treatment with the probiotic and then followed the larval development of Pecten maximus through the monitoring of survival rates, shell lengths and metamorphosis ability. Moreover, antioxidant (catalase and superoxide dismutase) and lipids peroxidation activities were also measured after bacterial challenge in order to evaluate the physiological response of larvae to pathogen exposition. Our results indicated an activation of the two selected antioxidant enzymes after bacterial challenge, but the increase was significantly lower in probiotic treated larvae. At the end of the experiment, the strain X34 treatment prevented a mass mortality event and showed a significant increase in the number of individuals reaching competence, when compared to untreated larvae.

Sperm characteristics of scallops have not been well described in the scientificliterature. The effects of sperm release technique (thermal shock versus serotonininjection), of sperm collection technique (testis sampling versus serotonin injection), ofsperm sampling location along the genital tract, of in vitro sperm maturation, and of timepost activation on scallop sperm characteristics were assessed in the present work.Whatever sperm release technique used, no significant differences were observed regardingthe percentage of motile spermatozoa and the velocity of the average path (VAP). Comparedto testicular sperm, a higher percentage of motile spermatozoa, VAP and intracellularadenosine triphosphate (ATP) content were observed for sperm shed after serotonininjection. From the distal part of testes up to the gonopore, an increase of thepercentage of motile spermatozoa and VAP was assessed, suggesting a sperm ‘maturationprocess’ along the genital ducts. A higher increase in the percentage of motile sperm wasrecorded during a 5 min incubation of testicular sperm in seawater containing 2 mMserotonin and seawater containing 10 mM caffein compared to seawater (control). Inaddition, a higher VAP was assessed, incubating testicular sperm in caffein, compared tocontrol or serotonin. Then, the percentage of motile spermatozoa, VAP and intracellularATP content exhibited a progressive reduction during the 10 h swimming period. Mean valuesof the percentage of motile spermatozoa, VAP, sperm track linearity (LIN) andintracellular ATP content recorded at the beginning of the movement period for spermsamples collected after intragonadal serotonin injection, were 82 ± 7%,162 ± 15μm s-1, 0.33 ± 0.12 and 212 ± 133 nmol × 10-9 spermatozoa (n = 9 males), respectively. The presentstudy confirms the existence of a sperm “maturation process” along scallop genital ducts.In addition, the cessation of scallop sperm movement can be explained by the exhaustion ofATP content at the end of the movement phase.

This paper deals with the economic impact of the invasion of a scallop fishery by an exotic shellfish that was accidentally imported some decades ago. The invasive alien species, a slipper-limpet, Crepidula fornicata, is a space competitor for local scallops, and its spread threatens the sustainability of the ongoing scallop restocking program. Facing this invasion, the local fisheries committee has initiated a containment project intending to make the restocking program consistent with the exotic species presence in the fishery. The issue is complicated by the occurrence of occasional toxic micro-algae blooms affecting the scallop fishery. The paper presents a model dealing with the economic impact of the invasive process, and a methodology for cost-benefit analysis of invasion management. According to numerical simulation, the invasion is a serious threat to the economic viability of the restocking program, and invasion management would help maintaining the long term sustainability of the fishery. Sensitivity tests highlight the importance of long term equilibrium scallop catches on the program result, depending on scallop farming technical performance and ecosystem disturbance.

The depuration kinetics of the domoic acid from three body parts (i) digestive gland, (ii) adductor muscle+gonad+kidney+foot and (iii) gills+mantle of the scallop Pecten maximus was studied over 154 days. The scallops, which had accumulated the toxins during a Pseudo-nitzschia australis outbreak, were obtained from a natural bed and hung from a mussel raft in two locations (front and centre) and at three depths (2, 6 and 10 m). The time course of the depuration of domoic acid (DA), as well as the environmental variables, were monitored throughout the experiment. The whole body depurated the toxin very slowly (ca 0.007 day−1) decreasing its concentration from ca. 3200 µg DA g−1. Its kinetics was driven mostly by the digestive gland, which accounted for ca. 95% of the total toxin burden from the start of the experiment. Suspending the scallops from a raft increased the depuration rate of the whole body and digestive gland (ca. 30%) and of the edible tissues (15%). Increases of the depuration rate of domoic acid seem to be related to the pair of covariating variables temperature-salinity. Food amount does not seem to have a significant effect.

In the present study, norepinephrine (NE), epinephrine (E), dopamine (DA) and 5-hydroxy-tryptamine (5HT) have been quantified by high performance liquid chromatography (HPLC) in Pecten maximus during larval and post-larval development. With average values ranging from 2 to 5 pg μg–1 of protein, NE remained low through the whole larval life, while epinephrine (E) was undetected. DA and 5HT were the most abundant monoamines with significant variations between larval, pre-metamorphic and post-larval stages. During the first 20 days, corresponding to D larval and umboned larval stages, levels of DA and 5HT increased from 15 to 30 and 10 to 15 pg μg–1 of protein, respectively. Then during the last week of larval life, at the approach of metamorphosis, DA rose sharply from 30 to 50 pg μg–1 of protein and 5HT from 15 to 50 pg μg–1 of protein. Lastly during the first week of post-larval life (day 27 to day 34) DA and 5HT contents declined to levels similar to those detected in the first days of larval life reaching progressively 1 pg μg–1 of protein during the second week of post-larval life (day 34 to day 55). These rapid and transient variations in monoamine contents (5HT and DA) around metamorphosis, present a great interest. However, this relation between neurochemical changes and metamorphosis must be confirmed with future studies in order to verify if such monoamines might be used as indicators of larval competence in P. maximus, a commercially important species.

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.

The digestive gland of Pecten maximus consists, as in other lamellibranchs, of numerous blindending tubules which communicate with the stomach by partially ciliated main ducts and non ciliated secondary ducts. The non-ciliated cells of the main ducts are characterized by a well developed brush border constituted by high and dense microvilli and a strong pinocytotic activity. Ciliated and non ciliated cells have a very similar fine structure. The digestive tubules have a large lumen and contain digestive cells at different stages of absorption, digestion and excretion, one part of the tubules being functional while the other is disintegrating. The dark crypts contain the flagellated secretory cells, characterized by a well developed granular endoplasmic reticulum, and the young immature cells which may replace both the secretory and digestive cells. The numerous lipid droplets occurring in the digestive duct cells and in the digestive cells reveal the lipid storage function of the digestive gland. Several enzyme activities involved in digestion have been localized in the digestive gland. High amylase activity and cellulase and lysozyme activities have been found in the ducts and in the tubules, whereas no proteolytic activity could be detected histochemically. Some intracellular peptidases and glycosidases have been localized in the cells of the digestive gland, especially in the brush-border cells of the ducts and in the functional part of the tubules. High alkaline and acid phosphatase activities are displayed by the duct brush-border cells and the digestive and secretory cells. These results show the main role of the digestive gland, both in extracellular digestion (secretion of the digestive enzymes) and in absorption and intracellular digestion and provide information on the respective functions of the different cells within these processes.

L'étude du déterminisme du pré-recrutement de Pecten maximus (L.) en baie de Saint-Brieuc a été réalisée par captage de post-larves sur des collecteurs artificiels, et par échantillonnage benthique des juvéniles de coquille Saint-Jacques et de la macrofaune épigée et endogée superficielle. Les techniques mises en œuvres fournissent des estimations fiables de l'abondance des pré-recrues et de la force d'une classe d'âge, dès les quatre premiers mois de vie benthique. L'abondance d'une classe d'âge pré-recrutée est déterminée par la fécondité des adultes, l'hydrodynamisme (courants; turbulence à l'interface eau-sédiment), la nature sédimentaire des fonds (degré d'envasement; substrats disponibles), la température hivernale des eaux, l'intensité des interactions biotiques (compétition; prédation), et par les facteurs régulant la croissance du groupe d'âge 0 (la survie lors du 1er hiver est fonction de la taille des juvéniles). Les trois années d'étude montrent l'existence d'une forte variabilité spatio-temporelle intra- et interannuelle des mécanismes régulant l'abondance du pré-recrutement de Pecten maximus.

This paper presents a summary of information on reproduction biology in the scallop, Pecten maximus, which is required for the successful reseeding and intensive aquaculture programs developed in France since 1982. Data are presented on the following subjects: environmental factors that sustain gametogenic activity and the time of year this activity occurs; biochemical changes that are associated with gametogenesis; the consistency of egg quality; and development of a simple test to predict egg quality.

Cet article propose un modèle empirique du recrutement du stock de coquilles Saint-Jacques, Pecten maximus (L.) en baie de Saint-Brieuc (Manche, France). Ce stock présente de fortes fluctuations du recrutement qui rendent inadéquate l'utilisation des modèles traditionnels de la dynamique des populations exploitées faisant appel à un état d'équilibre. Le modèle intègre trois variables: la biomasse féconde, les effets de l'effort de pêche sur les classes d'âge non exploitées et la variable « température ». Les corrélations entre les différentes expressions des paramètres et le recrutement sont systématiquement analysées. Le choix du modèle final repose sur la minimisation de la part inexpliquée de la variance totale. L'impact de l'effort de pèche sur les fluctuations du recrutement est testé sur deux saisons de pêche avant la mise en exploitation d'une cohorte (groupes d'âge 0 et 1), afin d'intégrer le régime d'exploitation dans le modèle final. Cette procédure révèle un effet plus significatif de l'effort de pêche exercé sur le groupe d'âge 0 de la cohorte.

Pour la température, les expressions initialement retenues sont les anomalies saisonnières, définies comme les écarts de température, par période mensuelle ou bimensuelle, par rapport à la température moyenne de la même période.

Les anomalies saisonnières n'ont pas conduit à une explication significative du recrutement; d'autres expressions de la température ont été recherchées. Elles sont définies comme des anomalies saisonnières pondérées par l'anomalie de l'année correspondante et sont appelées résidus thermiques. Les résidus thermiques sont utilisés sur des périodes mensuelles et bimensuelles en valeur algébrique et en valeur absolue. Les valeurs absolues des résidus thermiques par période bimensuelle fournissent les meilleurs résultats lors des ajustements. Seules les périodes contribuant significativement à l'explication du recrutement sont retenues. La détection de ces périodes critiques est faite par un test de FisherSnedecor. Cette procédure conduit à une combinaison multiplicative de la biomasse féconde, de la mortalité provoquée sur le groupe d'âge 0 par l'effort de pêche et des fonctions exponentielles de résidus thermiques en valeur absolue. Deux périodes critiques sont identifiées, la première quinzaine de mars et la seconde de juillet. La correspondance entre les deux périodes critiques d'anomalie thermique et des étapes du cycle de reproduction de l'animal (le début de la maturation sexuelle, la première ponte et le développement larvaire) est discutée. Le fait que les valeurs absolues semblent plus adéquates indique une adaptation de l'animal aux conditions thermiques moyennes du milieu. La température intervient donc comme un facteur régulant la dynamique de maturation sexuelle et de ponte. Sa rétention sous forme exponentielle multipliant la biomasse féconde traduit les fluctuations inter-annuelles de la fécondité réelle de la population.