This study examines the trophic status and relationships of coral reef fish in the lagoon of New Caledonia, southwest pacific. The feeding habits of 34 fish species collected at three contrasted sites were first described using a compilation of gut contents observations and data from the literature. The carbon and nitrogen isotope signatures of these fish and of some of their potential ultimate food sources were also determined at each site. Despite some spatial variations in the isotopic signatures of most food sources and fish trophic groups, the overall trophic structures of fish assemblages were similar at the three sites. Stable isotope data were then used to re-assign fish species to trophic groups based on the δ 15N signatures of fish and their food sources. Herbivorous fish species were clearly distinguished from the other trophic groups by their lower δ 15N signatures, consistent with an estimated trophic position of ~2 for all species examined. Scaridae were however characterized by relatively higher δ 13C and lower δ 15N, which is probably linked with the role of detritus in their diet. The estimated trophic positions of planktivorous fish species were consistent with their gut contents-based classification. Conversely, the isotopic signatures of carnivorous and piscivorous fish species largely overlapped, and their estimated trophic positions were much lower than expected. This suggests that these species feed over a broader range of trophic levels and food sources than implied by the gut contents observations, and indicates that their diet is partly omnivorous. Finally, the relationships between body mass and the isotopic signatures of four fish species were significant for at least one isotopic ratio for each species. Since ontogenetic variations and omnivorous diets are difficult to assess with gut contents data only, stable isotopes revealed essential in estimating the actual trophic status and relationships characterizing the fish species under study.

Contamination of shellfish by paralytic shellfish poisoning (PSP) toxins poses an economic threat to shellfish farmers. As contaminated shellfish cannot be harvested for long periods of time, it would be very useful to develop processes to optimise and shorten their detoxification. In this study, Pacific oysters Crassostrea gigas were first experimentally contaminated over a period of 13 days with a continuous flow of toxic Alexandrium minutum cultures at concentrations ranging from 150 to 200 cell ml-1 (toxin content after 13 days of contamination 438 $\mu $ g STX equiv. 100 g−1 wet weight). Then, two different detoxification treatments were tested and showed detoxification rates greater than those observed in coastal environments. The first treatment consisted of feeding oysters on Skeletonema costatum, at a concentration of 2000 cell ml−1 to speed up detoxification rates. The second detoxification method used the same Skeletonema costatum diet, supplemented with silt particles at a concentration of 20 mg L−1. A control was also set up by placing contaminated oysters in seawater with no additional algal food. The detoxification experiment lasted 8 days. Toxin contents were analysed by liquid chromatography with fluorescence detection (LC-FD). The S. costatum diet significantly reduced the time needed for oysters to reach the sanitary threshold (80 $\mu $ g STX equiv. 100 g−1 wet weight), but no effect of the silt supplement could be demonstrated conclusively. These different detoxification methods did not influence toxin biotransformations as observed in oyster tissues, i.e. epimerisation and decarbamoylation of gonyautoxins 2 and 3.

The occurrence of new phytoplankton species in a coastal area may be explained by the import of shellfish containing whole live algal cells in their digestive tracts. Indeed, shellfish containing toxic algal cells can induce both primary contaminations in safe areas (initially free from toxic microalgae), and secondary contaminations of other shellfish growing in the same area via the faeces of the imported animals. To mitigate this problem, shellfish need to be placed in a separate holding tank and their intestinal content purged. For a deeper understanding of the risks associated with transferring contaminated shellfish, oysters (Crassostrea gigas) and mussels (Mytilus edulis) were purposely fed either Alexandrium minutum or A. catenella (Dinophyceae) or Pseudo-nitzschia calliantha (Bacillariophyceae) toxic algae for 2 h. They were then transferred into individual tanks where they were continuously fed with a non-toxic alga, Tetraselmis suecica. Biodeposit production, faeces composition, and filtration rates were monitored for the shellfish over a 6-h period. The effect of temperature differences and different initial toxic algae concentrations were compared. This study revealed a relationship between temperature and cell lysis in the oyster digestive tract. It also indicated that toxic algae concentration did not seem to influence gut passage time in oysters, while a significant effect was observed in mussels, and confirmed the existence of a difference between oyster and mussel feeding patterns.

The taxonomic status of the cupped oysters Crassostrea angulata and C. gigas has received considerable attention in the last decades. Based on larval shell morphology, experimental hybridization, allozymes and nuclear DNA studies several authors have considered these two taxa as being synonymous. However, mitochondrial data showed clear genetic differences between the two taxa. In addition, microsatellite-based studies and cytogenetic studies have also provided evidence that supports their differentiation. Considerable differences have also been observed at the phenotypic level in terms of growth rate and ecophysiological parameters. In the present study, C. angulata from Sado estuary (Portugal) and C. gigas from Seudre estuary (France) were collected and factorial crosses were performed. Juveniles of the different progenies were reared in Ria Formosa (Portugal) under common conditions to determine if they exhibited differences in shell shape and in pigmentation of the adductor muscle scar. Significant morphometric differences between C. angulata and C. gigas progenies were indicated by univariate and multivariate analyses. Univariate analysis of size-adjusted shell measurements revealed significant differences between the two taxa for shell depth, muscle scar height, and length of ligamental area. Both reciprocal hybrids showed intermediate morphometric characters between parental lines. In addition, significant differences were also observed between C. angulata and C. gigas progenies in terms of pigmentation of adductor muscle scar. C. angulata and both reciprocal hybrid progenies showed highly pigmented adductor muscle scars whereas in C. gigas progeny the pigmentation was lighter. The differences in shell shape and muscle scar pigmentation observed in the present study support the distinction of the two taxa.

Parameters of hemocyte populations have been considered as relevant indicators of bivalve health and are currently used in immunotoxicological studies. Hemocytes in hemolymph can be collected by puncturing either the pericardial cavity or the adductor muscle sinus with a syringe. Flow cytometry is a methodological approach that is increasingly being used in laboratories for the study of hemocyte parameters in aquatic invertebrates. However, various protocols for hemocyte processing in laboratories equipped with different types of cytometers have been published. In this context, two flow cytometers (EPICS XL4®, Beckman Coulter and FacsCalibur®, Becton Dickinson) and two sites of hemocyte collection (pericardial cavity and adductor muscle sinus) were compared for the analysis of hemocyte parameters in the Pacific oyster, Crassostrea gigas. Hemolymph cells were analyzed in terms of their number and organelle contents. Cell mortality, phagocytosis, non specific esterase, extension of the lysosomal compartment and production of reactive oxygen species were quantified. The results showed that the phagocytic index was higher for hemocytes obtained in the muscle sinus hemolymph. The results are discussed with respect to the potential use of flow cytometry as a tool for hemocyte studies in bivalves.

Daily striae on the shell of the scallop, Argopecten purpuratus, were used to investigate its growth in a protected population within La Rinconada Bay, near Antofagasta (2nd Region, Northern Chile), and to determine how environmental forcings control shell growth. This sclerochronological approach was useful to describe daily shell growth a posteriori. Mean shell growth rates were calculated daily between February and October 1999 from shells of six specimens harvested on 15 October 1999. A multiple regression analysis performed on shell growth and environmental data shows that a temperature increase stimulates shell growth whereas particulate organic carbon concentration might be stressful above 2.5 mg L−1. The lunar cycle might also have an effect on growth, most potent around New Moons, by synchronizing an endogenous oscillator. The age at commercial size (90 mm) was only 10–11 months in La Rinconada Marine Reserve and the von Bertalanffy growth parameters were K = 2.24 y−1 and H ∞ = 117 mm. Differences in shell growth performances between this study and previous ones dealing with A. purpuratus growth may be explained by the different methods used for shell growth modelling, higher growth rate on the seabed compared to suspended cultures, and particular environmental forcings (e.g. El Niño Southern Oscillation-ENSO events). Growth performance seems better during La Niña than during El Niño events, probably because of the large temperature increase (above the highest temperatures recorded in “normal” conditions) and the decline in coastal upwelling (which affects food availability) during El Niño. La Rinconada Marine Reserve appears as a very favourable site for A. purpuratus growth, probably because of the active upwelling zone off Antofagasta. These new insights on A. purpuratus shell growth confirm the importance of La Rinconada Marine Reserve as an area supporting repopulation of endangered wild stocks and scallop aquaculture in Chile.

To protect public health, the European Commission established maximum levels of certain contaminants permitted in foodstuffs. The maximum amount of lead allowed in bivalve mollusc is 1.5 µg g−1 wet weight. In the Galician Rías, which are important areas of shellfish production in Spain, high levels of lead have been detected in the commercial bivalve Dosinia exoleta (Veneridae). Given the environmental and socio-economical problems this could represent, Pb concentration was tested in D. exoleta from two Rías, and the relation of lead accumulation with body size studied in detail. Implications for fisheries management are also discussed in this paper. Results showed a strong dependence of Pb accumulation on body size, with lead concentrations increasing exponentially with shell length. Larger animals presented a 5-fold increase in lead concentrations above the maximum permitted level. The size limit (length beyond which D. exoleta should not be extracted for commercial purposes) was initially established at 40 mm; but a more comprehensive geographical study of Pb concentrations in individuals from 35 to 40 mm long revealed that this size limit was not protective enough, and 35 mm is proposed as a safer limit.

The biochemical composition and biometry of different Artemia salina stages were determined in four ponds of increasing salinity (M1, M2, M3 and B1) in the Sfax solar saltern (Tunisia). Results showed the dominance of saturated fatty acids, which made up 48 to 57% of total fatty acids (FAs). Polyunsaturated fatty acids (PUFAs) 22:6(n-3) docosahexaenoic acid (DHA) and 20:5(n-3) eicosapentaenoic acid (EPA) represented on average only 3.1 and 4.0% of total FAs respectively. A. salina nauplii, cysts and metanauplii, in ponds M1, M2 and B1 respectively, were found to have optimal DHA/EPA ratios (>2) for use as live feed for invertebrate and fish larvae. Significant inter-pond variation in DHA/EPA levels was also recorded. The predominant FAs in Artemia were negatively correlated with both temperature and salinity. FA and protein contents were strongly affected by high temperatures (>30 °C) and probably by food sources (e.g., Dunaliella salina) (r = 0.9, n = 27). The density of Artemiasalina was positively correlated with protein content in pond B1. The high DHA/EPA ratios (1 to 3.3) found in this study indicate that Sfax Artemia could be a valuable food source for larvae in large marine hatcheries and also for some aquarium species.

Eighteen spermiating males were randomly selected from a hatchery-reared stock and electronically tagged to record changes in their sperm quality parameters (spermatozoa morphology, ultrastructure and motility, ionic composition and osmolality of the seminal plasma, and sperm volume and density) during the spawning season. Stripping was performed at the beginning of March, April and May. The Barbus barbus spermatozoon has a head without acrosome, a midpiece with 4–6 mitochondria and proximal and distal centrioles, and a flagellum with the typical 9+2 pairs of microtubules. Apart from posterior width of the midpiece, morphological and ultrastructural parameters changed significantly during the reproductive season; generally by decreasing toward the end of reproductive season. Sperm volume also decreased from 0.42 in March to 0.15 ml in May, and density from 18.81 in March to 12.45 × 109 spz ml−1 in May. Osmolality (mOsmol kg−1) was 268 ± 4, 276 ± 2 and 268 ± 2 in March, April and May respectively. Chloride, sodium, calcium and potassium ion concentrations (mM) did not show significant differences between March and April (Cl−: 125.3 vs. 120.5, Na+: 75.7 vs. 69.7, Ca2+: 0.4 vs. 0.3 and K+: 84.7 vs. 84.0). The percentage of motile spermatozoa at 15 s post activation did not show a significant difference between dates, but the highest spermatozoa velocity at 15 s post activation was observed in April (91.4 ± 3.2 µm s−1) and then decreased significantly towards the end of the reproductive season (80.6 µm s−1 in May). However, lowest spermatozoa velocity was measured in March (70.4 ± 1.9 µm s−1). This study supports the hypothesis that longer spermatozoa swim faster. Within one stripping, velocity and percentage motility decreased significantly with time post activation. In conclusion, changes observed in B. barbus sperm parameters during the reproductive season, suggest there is association between such changes and spermatozoa aging processes.

Despite extensive knowledge of the genetic structure of sea bass (Dicentrarchus labrax) populations, no studies have investigated genetic structure within early life stages, or compared such structure between such stages and (sub)adults. Using nine newly developed microsatellite loci, we investigated patterns of genetic variation and relatedness among juveniles that settled in two NW Mediterranean nursery grounds in close geographical proximity. There was no evidence for differentiation among samples at settlement (θ = -0.0010), and no significant genetic relatedness. Nevertheless, significant departures from Hardy-Weinberg equilibrium were detected in each sample, which could not be attributed exclusively to the presence of null alleles and to Wahlund effect. These results are compared with and discussed in relation to the genetic structure of adults described in the same area 10 years ago.