Rene Robert

Effect of food fatty acid and sterol quality on Pecten maximus gonad composition and reproduction process

Abstract Spawning individuals of the scallop Pecten maximus were conditioned on three test diets: Tahiti Isochrysis , a mixture (PTSC) and Chaetoceros calcitrans . The scallops fed T- Isochrysis showed a better hatching rate and lower atresia than those fed the other two diets. Proximate composition of the female gonads was not modified by the differences in the diets. Enrichment of gonads with sterol esters and triglycerides, characteristic of storage of lipids, observed with the broodstock fed the diatoms, did not result in successful gametogenesis and spawning. The monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) composition of neutral and polar lipids of gonads was related to the fatty acid composition of the diet. However, the 20 and 22 carbon PUFA were maintained at levels relatively independent of those of the diet; when these fatty acids were low in the diet, their concentration in the lipids of the gonads decreased but still remained significant. This effect was more pronounced in the polar than the neutral lipids. The preferential incorporation of 22:6 n − 3, 20:4 n − 6 and 20:5 n − 3 in the polar lipids indicates their role in gametogenesis and embryogenesis. The sterol composition of the gonads (free sterols and sterol esters) reflected that of the diet; however, the cholesterol, mainly found in the esterified fraction, was maintained at stable levels independent of dietary supply. Two sterols (22-dehydrocholesterol and 24-methylenecholesterol) that were either absent from, or present only in trace amounts in the diets, were found to occur at constant levels in the female gonads, regardless of the nature of the diet.

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

Abstract 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 industrys 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.

ReviewBivalve hatchery technology: The current situation for the Pacific oyster Crassostrea gigas and the scallop Pecten maximus in FranceÉcloserie de mollusques en France: situation actuelle de l'huître creuse Crassostrea gigas et de la coquille Saint-Jacques Pecten maximus

Abstract 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 industrys 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.

Temperature influence on pathogen transmission and subsequent mortalities in juvenile Pacific oysters Crassostrea gigas

Since 2008, mass mortalities of 1-yr-old Crassostrea gigas associated with the ostreid herpesvirus OsHV-1 μVar have occurred along all the coasts of France when seawater temperature reaches 16 to 17°C. The present study aimed to characterize the effect of temperature on oyster survival in combination with OsHV-1 DNA quantification by standard real-time PCR and total vibrio population levels in oyster tissues. To examine the effect of seawater temperature on disease transmission and related mortality of oysters, cohabitation experiments were conducted between healthy naive oysters and oysters previously exposed to field conditions in areas where mortalities were occurring. Oysters initially maintained in controlled conditions (free of mortality and negative for OsHV-1), and then transferred to an area where high mortalities were occurring among farmed stocks, became infected with OsHV-1 and exhibited high loads of vibrios followed by significant mortalities. When previously exposed oysters were maintained indoors at 13.0°C for 40 d and then at 20.6°C, they exhibited no mortality, were negative for OsHV-1 detection, and did not transmit the disease to healthy oysters. Survival of previously exposed oysters maintained indoors at 8 temperatures ranging from 13.4 to 29.0°C varied from 25 to 48% and was negatively correlated with holding temperature. Concomitantly, survival of naive cohabiting animals (62 to 98%) decreased with increasing seawater temperature until a plateau was reached between 16.2 and 21.9°C, and increased at higher temperatures. Therefore, the optimal temperature range for disease transmission from field-exposed to naive animals was between 16.2 and 21.9°C. Our results suggest that a long-term period (40 d) at low temperature (13°C) may offer a method of mitigating mortalities in oysters that have been exposed to an infective environment.

Growth, reproduction and gross biochemical composition of the Manila clam Ruditapes philippinarum in the Bay of Arcachon, France

Growth, reproduction and gross biochemical composition of the Manila clam Ruditapes philippinarum were studied for one oceanic and two inner stations in the Bay of Arcachon, France, from March 1989 to March 1991. During this period, sea-water temperature, salinity and chlorophyll a were also recorded. A marked increase in length occurred during the first year in all areas, after which growth rates decreased. In contrast, weight increased more steadily. The Manila clam exhibited best development in the oceanic area, but there was no difference in growth of clams between the two inner stations. Differences in growth between oceanic and inner stations may result from differences in fluctuations of environmental conditions such as temperature and salinity. Except for higher carbohydrate contents in clams recovered in autumn from the oceanic station “Le Ferret”, biochemical components differed little between stations. During the second winter, glycogen levels were relatively low, but no mortalities were recorded. On the other hand, sowing spat in autumn instead of spring or sowing larger-sized spat did not reduce the time required for culture of R. philippinarum.

A new photobioreactor for continuous microalgal production in hatcheries based on external‐loop airlift and swirling flow

This study deals with the scale of a new photobioreactor for continuous microalgal production in hatcheries. The combination of the state‐of‐art with the constraints inherent to hatcheries has turned the design into a closed, artificially illuminated and external‐loop airlift configuration based on a succession of elementary modules, each one being composed of two transparent vertical interconnected columns. The liquid circulation is ensured pneumatically (air injections) with respect to a swirling motion (tangential inlets). A single module of the whole photobioreactor was built‐up to scale its geometry (diameter and length) and to optimize its design (air sparger, tangential inlets). The volumetric productivities were predicted by modeling radiative transfer and growth of Isochrysis affinis galbana (clone Tahiti). The hydrodynamics of the liquid phase was modeled in terms of global flow behavior (circulation and mixing times, Péclet number) and of swirling motion decay along the column (Particle Image Velocimetry). The aeration performances were determined by overall volumetric mass transfer measurements. Continuous cultures of Isochrysis affinis galbana (clone Tahiti) were run in two geometrical configurations, generating either an axial or a swirling flow. Lastly, the definitive options of design are presented as well as a 120‐L prototype, currently implemented in a French mollusk hatchery and commercialized. Biotechnol. Bioeng. 2009;102: 132–147.

Preparation and assessment of microalgal concentrates as feeds for larval and juvenile Pacific oyster (Crassostrea gigas)

Abstract We assessed a flocculation method for preparing concentrates of seven microalgae. For five of these— Chaetoceros calcitrans (C.CAL), C. calcitrans forma pumilum [C.CAL(PUM)], Chaetoceros sp. (“ tenuissimus -like”) (C.TEN), Skeletonema costatum (SKEL) and Isochrysis aff. galbana (T.ISO)—we assessed flocculates as an 80% diet component in four experiments with larval and one with juvenile Pacific oysters. The remaining 20% diet component was T.ISO, except in Experiment 2 for larvae, where C.CAL(PUM) was used. The flocculates had been stored at 4 °C for 9–21 days and were compared against the corresponding fresh microalgae. For larvae (initial size, 74–82 μm), best growth was usually seen in diets containing C.CAL(PUM). In Experiment 1, larvae fed an 80% C.CAL(PUM) (live) diet increased to 248 μm after 16 days. This growth was ≥50% more than with diets containing C.CAL(PUM) (concentrate) or C.CAL (live or concentrate). In Experiment 2, larvae fed C.CAL(PUM) (live) as the 20% basal ration (control) grew to 167 μm. Supplementation of this diet with live or concentrated T.ISO as the 80% component did not improve larval growth. In Experiment 3, larvae fed an 80% C.CAL(PUM) (concentrate) diet grew as well as larvae fed the 80% C.CAL(PUM) (live) diet (192 and 194 μm, respectively) and more than larvae fed 80% C.TEN (live or concentrated; 155 and 162 μm, respectively). In Experiment 4, larvae fed 80% live SKEL diet (125 μm) grew more than larvae fed SKEL (concentrate) or C.CAL (live or concentrate) (larvae, 104–112 μm). Over all experiments, larval survival ranged from 2% to 90% and was reflected in changes observed for larval growth. For juvenile oysters, a basal 20% T.ISO diet alone gave moderate growth after 28 days ( k =0.031 day −1 ). Supplementation with a SKEL concentrate improved growth ( k =0.054 day −1 ), whereas supplements of live or concentrated forms of either C.CAL(PUM) or C.TEN gave the best growth ( k =0.083–0.090 day −1 ). This study demonstrated that flocculated concentrates of microalgae, especially C.CAL(PUM) or C.TEN, can be used effectively as major dietary components for larval and juvenile oysters.

Incorporation of Microalgae Sterols by Scallop Pecten maximus (L.) Larvae

Changes in sterol composition of Pecten maximus larvae during the larval development stage with standard algal mixtures and unialgal diets were analysed. The sterol composition of four microalgae currently used in mollusc hatchery were also examined. Under standard algal conditions, the larvae quickly use the steryl ester from larvae reserves during the endotrophic and the mixotrophe phases. The preferential incorporation of Pavlova lutheri and T-Isochrysis sterols, rather than Skeletonema costatum sterols, during the larval development stage would indicate that S. costatum cells were poorly ingested and digested by larvae. Among the ingested sterols, cholesterol and stigmasterol were preferentially incorporated by the larvae. Conversely, the larvae appeared able to limit the incorporation of methylpavlovol, ethylpavlovol, and 4alpha-methylporiferasterol. In the unialgal experiment, the best growths were obtained with the diet richest in cholesterol (Chaetoceros calcitrans) and the best compromise of good growth and settlement rate was observed with the diet richest in C24 ethyl sterol. The selective incorporation of the cholesterol was confirmed by the larval rearing with C. calcitrans. The strong sterol dietary imprint in larvae corroborated the absence of an important capacity in P. maximus larvae to convert or biosynthesise sterol.

Use of fresh and preserved Tetraselmis suecica for feeding Crassostrea gigas larvae

Abstract In an attempt to provide cost-effective alternative diets and to simplify hatchery–nursery procedures, substitutes for live microalgae in mariculture were tested and among them, concentrated microalgae have so far appeared to be the best alternative products for bivalves, though there are few experimental studies. The food quality of fresh and preserved Tetraselmis suecica for umboned Crassostrea gigas larvae was studied here and its potential as an algal feed for remote production was evaluated. Because it leads to lower growth and higher mortalities than the control diets (>60%), the use of T. suecica OR (strain Orbetello) for C. gigas larvae is not recommended as a monospecific diet. However, a binary diet that includes T. suecica OR is as efficient as the standard ternary PTC diet for C. gigas larvae. On the other hand, even though microalgal utilisation was not clearly affected by the initial size of the larvae, it seemed that old umboned larvae took full advantage of T. suecica OR. Its usefulness in C. gigas larval rearing is therefore limited, but its potential for oyster spat feeding has to be considered. Lastly, preservation at low temperature is an efficient method to maintain the food value of T. suecica OR.

Mortality control of scallop larvae in the hatchery

Larval mortalities occurring in molluscan hatcheries have often been associated with bacterial contamination, and more specifically with vibrios. Although batches of oyster and clam larvae have been routinely reared in the hatchery of Argenton (North Brittany, France) without antibiotics, high larval mortalities have been recorded with the great scallop, Pecten maximus, under similar conditions. For this species, an addition of antibiotics was found necessary and chloramphenicol was used at a concentration of 8 mg l−1. However, this chemical has now been banned in Europe, making either substitution products or an improvement in the rearing procedures essential. Studies carried out have shown that neither a decrease in larval density (to 1 larva ml−1) nor an increase in seawater change frequency (to one per day) had any positive effects. Furthermore, elective substances such as sugars were not suitable and the use of another antibiotic, erythromycin, led to inconsistent results. The only positive effects were obtained with lower levels of chloramphenicol, which does not resolve the problem. Because no alternative solutions have as yet been found, further research needs to be undertaken.