Review of the reproductive physiology of the scallop,

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

A preliminary study of the behaviour and vitality of reseeded juvenile great scallops, of three sizes in three seasons

In order to have a better understanding of recessing in great scallop, Pecten maximus and consequently the causes of mortality at reseeding, this study has monitored, at different seasons, the dispersion and recessing of different sizes of juveniles (about 15, 30 and 45 mm, called small, medium and large) after seeding. Moreover, the aim was to see when small spat (15 mm) could be seeded, and thus reduce the costs of intermediate culture. Three monitoring approaches were used together: (1) continual observations by remote video camera, of a defined area (less than 1 m2) containing 10 scallops from each size group; (2) daily monitoring of behaviour with divers along three bottom lines, with 20 × 1 m2 plots each and nine marked scallops per plot; and (3) the biochemical content of the muscle: adenylic energetic charge and storage of energy reserves (glucides, proteins, lipids). The video monitoring identified but did not quantify predator behaviour, particularly at night. The role and behaviour of spiny crab, Maia squinado, and of small predators has clearly been shown, such as: (a) small crustaceans, Inachus sp., breaking the edges of scallop valves; and (b) small gobies, Pomatoschistus pictus, pecking the tentacles of the scallop mantle. For the monitoring by divers, filtering appeared much too difficult to look at for it was very disturbed by divers, and anyway the resumption of filtering came immediately after seeding. On the other hand, diver monitoring of dispersal and recessing was quite easy to do with a minimum of practice. On the basis of dispersal, the best seasons for seeding appear to be spring or summer. In autumn, two-thirds of small and medium juveniles are missing 3 days after seeding, but we could not observe whether they had been eaten by predators or had just moved and recessed farther. There was no experiment in winter owing to adverse conditions for scallop seedings. Biochemical analyses confirmed the unsuitability of autumn for scallop seeding, because of very low glucide content in this season. The adenylic energetic charge in the smooth part of the muscle showed that stress before seeding (aerial exposure, handling), and post-seeding behaviour (swimming, recessing) have a high energetic cost for scallops. In summer and autumn, 3 days after seeding, none of the three size batches recovered their initial vitality

Prospection "Pectinides" (mollusques, bivalves) dans le lagon S.W. de Nouvelle-Calédonie (région de Nouméa). Rapport de la mission CORDET-1983

Le but principal de cette mission était de compléter les quelques observations disponibles par des données précises permettant de statuer sur l'opportunité d'étudier plus à fond la biologie et la dynamique de population de certains de ces Pectinid dans une optique d'exploitation essentiellement par pêche artisanale

Influence of diet assemblage on Ostrea edulis broodstock conditioning and subsequent larval development

In contrast with the Japanese oyster Crassostrea gigas and the Manila clam Ruditapes philippinarum, Ostrea edulis seed production in the hatchery has been reported to be erratic, with sudden and unexplained larval and post-metamorphosis mortalities. Fecundity and initial larval quality have been related to broodstock conditioning, but effects on larval development and metamorphosis remain poorly understood. In addition, molluscan larval mortalities have been often associated with bacterial contamination and flow-through techniques may help to overcome this problem. Both aspects have been considered in the present work. O. edulis broodstock were conditioned at 19 °C and fed three different microalgal diets. Two were single-species diets: Rhodomonas salina (Rs) or Thalassiosira weissflogii (Tw) and the third was a combination of both species (RsTw: 50/50 in equivalent cell volume). Mean fecundity, expressed as mean number of larvae released by oysters fed different diets, was 0.16, 0.28 and 0.39 million, respectively; whereas, mean larval size at release differed significantly from 174 to 181 µm. Moreover, when broodstock were fed combined assemblage (RsTw), larval release occurred more consistently. Larvae were subsequently fed two different diets over an 11-day period: Chaetoceros gracilis solely (Cg) or a bi-specific assemblage (T: Isochrysis affinis galbana plus Cg). Larval growth ranged from 5.5 to 7.4 µm d-1 for larvae fed Cg and was generally higher (8.1 µm d-1) in larvae fed the mixed diet TCg. On day 11, larval survival and competence ranged from 50 to 75% and 40 to 70% respectively, these results being closely related to broodstock nutrition. On day 18 larval settlement ranged from 1 to 60%. When analyzing overall performance, from fecundity to settlement, best results were obtained with broodstock, fed the bi-specific diet (RsTw), which released numerous larvae over a short period with satisfactory larval development and high metamorphosis, and these larvae also fed bi-specific diet, TCg

Effects of hydrodynamic factors on Pecten maximus larval development

WOS:000412517900003International audienceHatchery production of great scallop, Pecten maximus, remains unpredictable, notably due to poor larval survival. Large-scale flow-through systems up to 3500 L have been developed to avoid the use of antibiotics in static systems. Alternatively, small-scale flow-through systems have been successfully applied for oysters but they proved to be unsuitable to rear scallop larvae. By focusing on physical factors presumed to limit P. maximus larval development, this study aimed to optimize great scallop larvae rearing parameters under controlled conditions. First, the influence of aeration on larval performances, energetic metabolism and antioxidant defences were studied both in static and flow-through systems. Aeration depressed larval food intake, regardless of the intensities of flow tested (100 ml/min, 155 ml/min and 270 ml/min). On the other hand, antioxidant enzyme activities remained constant or decreased, suggesting that antioxidant defences were inactivated. The increase in citrate synthase activity suggested an increase in metabolic rate possibly due to a turbulent stressful environment. All larvae exposed to such turbulence died before reaching metamorphosis, whereas those reared without aeration survived well (approximate to 95%). The effects of water renewal were thereafter studied in 50-L flow-through flat-bottomed tanks. No differences in survival (20.4 +/- 0.5%), growth (3.8 +/- 0.2 lm/d), competence (5.6 +/- 0.2%), energetic metabolism level and antioxidant enzyme activities were observed when comparing 12.5 and 25 L/hr water renewal. Whereas air bubbling leads to detrimental effects, flow-through in small flat-bottomed tanks appears to be a suitable technique for scallop larvae rearing

Cryopreservation of great scallop (

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

Anaesthesia and gonad sampling in the European flat oyster (Ostrea edulis)

Controlled reproduction of the European flat oyster requires the development of tools adapted to this species, including a practical anaesthesia and gonad sampling protocol to facilitate sex determination and the verification of gametogenesis. Three replicate groups of 10 oysters (mean weight +/- SD: 29.9 +/- 8.5 g) were anaesthetised in 5 L containers using magnesium chloride designed either for laboratory (Flucka (R)) or agricultural (Dead Sea Work (R): DSW) use, at two concentrations (50 or 72 g L-1). No significant differences were observed in the percentages of oysters anaesthetised or subsequent oyster mortality with the different anaesthetics or concentrations, but increasing water temperature from 14.9 to 18.8 degrees C significantly increased the number of oysters anaesthetised after 3 h. Increasing anaesthesia duration from 1 to 22 h significantly increased the percentage of oysters anaesthetised but did not affect subsequent oyster mortality. Gonad sampling of anaesthetised oysters did not increase oyster mortality either. A reliable anaesthesia protocol was, therefore, defined using 50 g L-1 DSW (R) magnesium chloride for a 2 to 3 h duration. This protocol was validated by monthly anaesthesia and gonad sampling on the same oysters over a three month period, during which a percentage of 95 +/- 2% anaesthetised oysters was observed. Compared with controls (oysters that were neither anaesthetised nor sampled), oyster mortality of monthly anaesthetised batches showed no significant increase. (C) 2010 Elsevier B.V. All rights reserved

Oyster sex determination is influenced by temperature — First clues in spat during first gonadic differentiation and gametogenesis

International audienc

Effect of sampling location, release technique and time after activation on the movement characteristics of scallop (Pecten maximus) sperm

Sperm characteristics of scallops have not been well described in the scientific literature. The effects of sperm release technique (thermal shock versus serotonin injection), of sperm collection technique (testis sampling versus serotonin injection), of sperm sampling location along the genital tract, of in vitro sperm maturation, and of time post activation on scallop sperm characteristics were assessed in the present work. Whatever sperm release technique used, no significant differences were observed regarding the percentage of motile spermatozoa and the velocity of the average path (YAP). Compared to testicular sperm, a higher percentage of motile spermatozoa, YAP and intracellular adenosine triphosphate (ATP) content were observed for sperm shed after serotonin injection. From the distal part of testes up to the gonopore, an increase of the percentage of motile spermatozoa and YAP was assessed, suggesting a sperm 'maturation process' along the genital ducts. A higher increase in the percentage of motile sperm was recorded during a 5 mm incubation of testicular sperm in seawater containing 2 mM serotonin and seawater containing 10 mM caffein compared to seawater (control). In addition, a higher YAP was assessed, incubating testicular sperm in caffein, compared to control or serotonin. Then, the percentage of motile spermatozoa, YAP and intracellular ATP content exhibited a progressive reduction during the 10 h swimming period. Mean values of the percentage of motile spermatozoa, YAP, sperm track linearity (LIN) and intracellular ATP content recorded at the beginning of the movement period for sperm samples collected after intragonadal serotonin injection, were 82 +/- 7%, 162 +/- 15 mu m s(-1), 0.33 +/- 0.12 and 212 +/- 133 nmol x 10(-9) spermatozoa (n = 9 males), respectively. The present study 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 of ATP content at the end of the movement phase

The quality of great scallop (Pecten maximus) sperm after thawing

International audienceMost publications devoted to the cryopreservation of mollusc sperm have focused on the definition of technical protocols, avoiding the description of sperm quality after thawing. The present study investigated the effects of cryopreservation on sperm quality in the great scallop. Wild scallop were fished during the natural spawning period and conditioned in the hatchery before use. Sperm samples were obtained after intragonadal injection of serotonin and cryopreserved using a previously published protocol.ăăSperm quality was assessed using a panel of four parameters: sperm motility characteristics, using a a computer assisted sperm analysis plugin with Image J, intracellular ATP content using an ATP-Lite kit, sperm integrity, using flow cytometry and sperm morphology, using transmission electron microscopy. For each parameter, fresh (control) and thawed spermatozoa were compared.ăăA significant decrease of both the percentage of motile spermatozoa (reduction: 75%) and sperm swimming speed (86%) were observed for thawed sperm compared with fresh sperm. The percentage of living spermatozoa, as assessed using flow cytometry, was significantly lower for thawed sperm (72.4 ± 2.5%) compared with fresh sperm (86.4 ± 1.1). However, no significant difference of intracellular sperm ATP content was observed between fresh and thawed sperm. Post thawing, while some spermatozoa showed little or no morphological differences compared with fresh sperm, others had undergone drastic changes, including swelling of the plasma membrane, structural alterations of the chromatin and damage to mitochondria.ăăIn conclusion, the descriptive parameters studied in the present work showed that the quality of thawed great scallop sperm was lower than that of fresh cells but was still sufficient for use in aquaculture programs and sperm cryobanking for this species