Ultrastructural characterisation of Marteilia species (Paramyxea) from Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis in Europe

A focused ultrastructural study of Marteilia spp. found in cultured Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis from France and Spain was conducted with emphasis placed on haplosporosomes, striated plate-like inclusions and spore wall morphology. Two types of haplosporosome were identified, sphaeroid and oblate, which were common to the parasite in all 3 host species. A total of 492 haplosporosomes were measured; those from the Marteilia sp. in Mytilus spp. were marginally smaller than those in Ostrea edulis. Spore wall morphology was found to vary depending on the state of maturity of the parasite--the more mature the parasite, the thicker the wall surrounding it. It is suggested that the current criteria used to distinguish M. maurini from M. refringens are invalid and that M. maurini was relegated to a junior synonym of M. refringens.     

Ribotyping of vibrio populations associated with cultured oysters (Ostrea edulis)

The intraspecific variability of Vibrio splendidus, V. harveyi and V. tubiashii recovered from oysters (Ostrea edulis) collected at the Mediterranean coast near Valencia, Spain, was analyzed by ribotyping. The two former species represented the most abundant ones, and the third one was the only species described as pathogenic for oysters. A total of 115 environmental strains were studied, 84 of V. splendidus, 23 of V. harveyi and 8 of V. tubiashii. Chromosomal DNA was digested with KpnI and hybridized with an oligonucleotide probe complementary to a highly conserved sequence in the 23S rRNA gene. Ribotyping among natural populations of the three species rendered 5 to 9 bands, and showed a high genetic diversity, with a ratio no. of strains/no. of ribotypes between 1.1 and 1.5. Cluster analysis of V. splendidus ribotypes suggests a seasonal pattern of incidence, with those ribotypes corresponding to winter and spring samples being maintained in the oysters over the year.     

The estuarine biology of the River lamprey, Lampetra fluviatilis, in the Firth of Forth, Scotland, with particular reference to size composition and feeding

Samples collected regularly during 1979, 1980 and 1981 from the intake screens of power stations in the estuary of the River Forth produced data on the estuarine phase in the life cycle of the River lamprey, Lampetra fluviatilis. Recently metamorphosed animals were common during the spring while sexually maturing adults were abundant in the late summer and autumn. These were assumed to be lampreys at the end of their downstream and start of their upstream migrations respectively. The respective sizes of the presumed downstream and upstream migrants were 69–135 mm (0-2-2-8 g) and 200–361 mm (7-0-93-2 g). Smaller numbers of animals of intermediate size were collected during the summer and late autumn. Males were usually the predominant sex with an average of 56–5% of the population in 1980–1981. In all months, the mean weight and with one exception also the mean length, was greater for females than for males. The intestine frequently contained fish remains, especially muscle, bone and scales of clupeids and thus the River lamprey seems to feed mainly on teleosts in this estuary. An analysis of the size of scales in the intestines of lampreys of various body lengths indicates that there is a relationship between the size of host and predator. Comparisons with other studies of Lampetra fluviatilis emphasize the variability that exists in aspects of the biology of this species within and among populations.     

Enzyme polymorphisms in the European oyster, Ostrea edulis L.

Extracts of the digestive diverticula of more than 300 individuals from four geographically separated populations of the European oyster, Ostrea edulis L. have been examined by electrophoresis for esterase and phosphoglucose isomerase polymorphisms. Three regions of esterase variability have been detected in the electrophoretograms. It is inferred that the variants in two of these regions are governed by two co-dominant alleles at each of two loci. Two phenotypes of phosphoglucose isomerase, which is inferred to be a dimeric enzyme encoded by two alleles at a single locus, have been observed. Allele frequencies and phenotype distributions are compared in the four populations. It is concluded that the populations differ genetically at the loci investigated, the magnitude of the differences being generally greatest between different 'physiological races'.     

Combining Two-Stage Testing and Interval Mapping Strategies to Detect QTL for Resistance to Bonamiosis in the European Flat Oyster Ostrea edulis

We have identified quantitative trait loci (QTL) in the flat oyster (Ostrea edulis) for resistance to Bonamia ostreae, a parasite responsible for the dramatic reduction in the aquaculture of this species. An F₂ family from a cross between a wild oyster and an individual from a family selected for resistance to bonamiosis was cultured with wild oysters injected with the parasite, leading to 20% cumulative mortality. Selective genotyping of 92 out of a total of 550 F₂ progeny (i.e., 46 heavily infected oysters that died and 46 parasite-free oysters that survived) was performed using 20 microsatellites and 34 amplification fragment length polymorphism primer pairs. Both a two-stage testing strategy and QTL interval mapping methods were used. The two-stage detection strategy had a high power with a low rate of false positives and identified nine and six probable markers linked to genes of resistance and susceptibility, respectively. Parent-specific genetic linkage maps were built for the family, spanning ten linkage groups (n = 10) with an observed genome coverage of 69–84%. Three QTL were identified by interval mapping in the first parental map and two in the second. Good concordance was observed between the results obtained after the two-stage testing strategy and QTL mapping.     

Carotenoids in Ostrea edulis L. (Bivalvia: Ostreacea) from the lagoon of Venice (Italy)

By means of columnar and thin-layer chromatography the presence of carotenoids in Ostrea edulis L. (Bivalvia: Ostreacea) from the Lagoon Venice (Italy), was studied.The following carotenoids were founds: -, -, -carotene, -carotene epoxide, lutein (free and epoxide from), zeaxanthin, diatoxanthin, mutatoxanthin and astaxanthin. The dominating carotenoids were lutein.The total contents varied within the range of 5.4–8.1 µg/g wet weight.     

Source levels and the estimated active space of bottlenose dolphin (Tursiops truncatus) whistles in the Moray Firth, Scotland

This study measured SPLs of whistles of wild bottlenose dolphins (Tursiops truncatus) in the Moray Firth, Scotland, and estimated their active space, i.e. the distance at which another dolphin can perceive the whistle of a conspecific. Whistling dolphins were localized with a dispersed hydrophone array by comparing differences in the times of arrival of a whistle at different hydrophones. The mean source level for whistles was 158 +/- 0.6 dB re. 1 microPa. The maximum was 169 dB re. 1 microPa. The active space of these whistles was calculated taking into account transmission loss, ambient noise, the critical ratios and the auditory sensitivity of this species. The estimated radius of the active space of unmodulated whistles between 3.5 kHz and 10 kHz produced at maximum source level ranged from 20 km to 25 km in a habitat of 10 m depth and at sea state 0. At sea state 4 it ranged from 14 km to 22 km. For whistles of 12 kHz it dropped to 1.5-4 km. The results suggest that whistles can be used to maintain group cohesion over large distances but also that dolphins that researchers consider to belong to separate groups might be in acoustic contact.     

Seasonal variation in the diet of common seals (Phoca vitulina) in the Moray Firth area of Scotland

Seasonal variation in the diet of common seals ( Phoca vitulina ) in the Moray Firth, north-east Scotland, was determined from analysis of faecal samples collected at haul-out sites during each month of 1988. Data on diet of common seals in 1987 are also presented. Limitations of the methods available for quantification of diet are discussed. Although some of the observed variation in diet from month to month may reflect changes in the sampling regime, a clear seasonal pattern was apparent, with clupeids predominating in the winter and sandeels in the summer. The trends observed are consistent with opportunistic feeding on the most abundant Prey.     

Branchial lesions associated with abundant apoptotic cells in oysters Ostrea edulis of Galicia (NW Spain)

An experiment to evaluate differences in growth, mortality and disease susceptibility among Ostrea edulis stocks was performed. Five families were produced from each of 4 oyster populations (Irish, Greek and 2 Galician). The spat were transferred to a raft in the Ria de Arousa (Galicia, Spain) for grow-out. Monthly samples of each family were histologically processed from 2001 to 2003. One of the pathological conditions discovered by this study was the occurrence of extensive branchial lesions characterized by haemocytic infiltration and loss of branchial architecture. Furthermore, abundant atypical cells occurred among the haemocytes in the lesions in the branchial connective and epithelial tissues, but rarely in the mantle. These cells were contracted in size with nuclei showing chromatin condensation and fragmentation. Some nuclear chromatin aggregated under the nuclear membranes into crescent shapes, whereas others were uniformly dense. Those characteristics suggested that the cells were apoptotic haemocytes, which was confirmed by transmission electron microscopy (TEM) and by a terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labelling (TUNEL) assay using the Apoptag Kit on paraffin sections. A low prevalence of gill lesions was detected in some, but not all, families of every origin peaking in July 2002 and April 2003. No etiologic agent was identified by either histology or TEM; thus, the cause of the abundance of apoptotic cells remains unclear.     

Effects of cooling and freezing on the motility of Ostrea edulis (L., 1758) spermatozoa after thawing

The aim of this work was to evaluate the effects of temperature, cryoprotectant agents and freezing curves on sperm motility of Ostrea edulis. All phases of cryopreservation were studied (evaluation of semen motility pattern, choice of cryoprotectants and freezing rates) to restore after thawing the motility characteristics distinctive of fresh semen.To assess the temperature effects on sperm motility, semen was activated using four different temperatures (25, 18, 10 and 3 °C). Sperm aliquots were maintained inactive at these temperatures for 1 and 3 h, then activated with FSW at same temperature of conservation. Sperm was activated and incubated to 3 °C with dimethylsulfoxide (Me₂SO), ethylene glycol (EG), 1–2 propylene glycol (PG) (5%, 7%, 10% and 15% final concentrations), glycerol (GlOH; 5%, 10% and 15% final concentrations) and methanol (MetOH; 4% and 10% final concentrations) for 10, 20 and 30 min. A first evaluation of freezing rates was made by testing four freezing curves: −1, −3, −6 and −10 °C/min. Then, an optimization was made by testing four freezing curves: −2.5, −3.0, −3.5 and −4 °C/min.The selected temperature for short term conservation has been 3 °C, because only this temperature has allowed good sperm motility conservation after 3 h of dry-storage; this is a time sufficient to conduct cryopreservation procedures. The sperm showed a particular sensitivity to GlOH and PG to all tested concentrations and to 15% Me₂SO. EG and MetOH to all concentrations and Me₂SO to concentrations lower than 15% have not shown significant toxic effects. The freezing rate −3 °C/min using 15% EG has shown an highest percentage of RVF (rapid, vigorous and forward) spermatozoa (class 3, about 75% of fresh semen) and an highest sperm motility duration.     

Reduced female gene flow in the European flat oyster Ostrea edulis

The geographical structure of 15 natural populations of the flat oyster (Ostrea edulis L.) was assessed by single-strand conformation polymorphism (SSCP) of a 313-base-pair (bp) fragment of the mitochondrial 12S-rRNA gene. Fourteen haplotypes were observed, with one being dominant in the Mediterranean samples and another one in the Atlantic populations. The geographically extreme populations sampled in Norway and the Black Sea appeared differentiated by exhibiting the dominance of a third group of haplotypes. The results were compared to available microsatellite data at five loci. The Atlantic/Mediterranean differentiation pattern was qualitatively the same with both types of markers, confirming an isolation-by-distance pattern. The average mitochondrial haplotypic diversity displayed a high among populations variance, reflecting small effective population size in some locations. Additionally, a 10-fold quantitative difference was observed in Fst between the mitochondrial and the nuclear genomes, which could be due to an unbalanced sex ratio or sex-biased differential reproductive success between males and females (or both).     

Characterization of 27 microsatellite loci in the European flat oyster Ostrea edulis

The flat oyster Ostrea edulis is native to Europe and populations have been severely depleted by the parasite Bonamia ostreae since the 1980s. Additional genetic markers are required to improve population genetics study and linkage map development for selection for B. ostrea-resistance in this species. Here, we characterized 27 novel microsatellite loci for O. edulis. Number of alleles per locus ranged from 6 to 25 and observed heterozygosity between 0.375 and 1. Null alleles were suggested at a few loci but most loci were in Hardy-Weinberg agreement enabling their reliable use in further population and mapping genetics approaches.