Larvae of the coral reef damselfish Acanthochromis polyacanthus (Bleeker) were fed either unenriched Artemia nauplii or nauplii which had been enriched by pre-feeding with microcapsules containing either squid oil (SQO) or cod liver oil (CLO). Enriched nauplii contained elevated levels of the n-3 highly unsaturated fatty acids (HUFA) eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) which made up 5.22 ± 0.34 and 2.62 ± 0.28 %, respectively, of total fatty acids in nauplii enriched with CLO, and 10.48 ± 0.36 and 3.43 ± 0.33 %, respectively, in nauplii enriched with SQO. In contrast, unenriched nauplii contained EPA (5.03 ± 1.04 %) but did not contain DHA. Survival differed significantly between treatments over the 18-d study; larvae receiving CLO enriched nauplii showed 100 % survival and those receiving SQO enriched nauplii showed 93.3 ± 6.6 % survival. In contrast, only 46 ± 6.7 % of larvae receiving unenriched nauplii survived to the end of the 18-d study. Wet weight, dry weight and proximate biochemical composition did not differ significantly between treatments at the end of the study. Mean standard length of larvae fed CLO enriched nauplii was significantly smaller than that of larvae fed SQO enriched nauplii; however, neither differed significantly from larvae fed unenriched nauplii. The fatty acid composition of A. polyacanthus larvae was significantly influenced by the fatty acid composition of the diet. The results indicate that A. polyacanthus larvae are unable to synthesise DHA from available dietary precursors and, as such, dietary DHA is required to maximise survival. Development of appropriate culture techniques for the larvae of coral reef fishes will allow controlled laboratory studies with these species and may eventually reduce pressure on wild populations exploited for the aquarium trade.

The aim of the work presented in this paper was to assess the relative efficiency of the GOC 73 sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) compared with that of a typical Italian commercial trawl. The latter was chosen because it is commonly used by fishermen in the central Adriatic, where the experiment was conducted, and therefore appeared as the best possible sampler of the commercial species present in those areas. Moreover, this trawl is similar to the various trawls used for the Italian national survey programme (GRUND). Four fishing trips were conducted between 1996 and 1997 in different areas and seasons to sample different species. Each trip was conducted in the same fishing area. A codend cover mounted on the commercial trawl ensured that the codends of the two nets had the same mesh opening. The two trawls were alternated daily. Net geometry (horizontal and vertical net opening) was measured during all tows. Catch data were converted into abundance per swept area before comparing the trawls. Efficiency comparisons were performed on ten fish species, one crustacean and four molluscs belonging to the MEDITS list of main reference species. The MEDITS trawl was significantly less efficient in terms of both weight and numbers of individuals fished for hake (Merluccius merluccius), common sole (Solea vulgaris) and Norway lobster (Nephrops norvegicus). A highly significant difference in favour of the commercial trawl was found in the weight, but not the numbers, of common pandora (Pagellus erythrinus). Efficiency differences were negligible for red mullet (Mullus barbatus), while the MEDITS trawl was significantly more efficient for the numbers of Atlantic horse mackerel (Trachurus trachurus). For all the other main reference species differences were not significant. The commercial trawl was more efficient for large individuals of some species. The relative efficiency of the MEDITS trawl was especially low for small-size classes of N. norvegicus. The results confirm the lower efficiency of the MEDITS compared with the commercial Italian trawl for benthic species, and its greater efficiency for some others released from the bottom as well as for the pelagic ones. These data allow the results of the MEDITS surveys to be compared with those of the GRUND programme and with commercial-fleet catches in areas where the commercial trawls used are similar to the one studied here.

Results on changes in the total amino acids (protein bound + free) and the free amino acids (FAA) in relation to development, from egg (unfertilised and/or fertilised) to yolk-sac resorbed larva, before first feeding, in two Percichthyid fish, trout cod, Maccullochella macquariensis and Murray cod. Maccullochella peelii peelii, which lay demersal, adhesive eggs, are presented. Throughout development, the FAA accounted for only a small proportion (0.19% in fertilised eggs of both species) of the total amino acid pool. Nine essential amino acids (EAA) and eight non-essential amino acids (NEAA) were quantified in the amino acid pool at all stages of development. In both species, the total amino acid content decreased during the transformation (at 20 ± 1 °C) from newly hatched larva to yolk-sac resorbed larva. Overall, the changes in the TEAA and TNEAA reflected that of the amino acid pool. In trout cod, all but one EAA (lysine) and two NEAA (cysteine and glycine) decreased with ontogeny, from fertilised egg to yolk-sac resorbed larva. In Murray cod, however, the exceptions to the general decline were two NEAA (aspartic acid and glycine). In contrast, the FAA increased with development, the changes being reflected in both FEAA and FNEAA. Qualitatively, the predominant free amino acids in trout cod and Murray cod eggs were alanine, lysine, leucine and serine. Because the egg protein and the total amino acid contents declined with development, it is concluded that the rate of breakdown of yolk protein was higher than the anabolic and catabolic processes during embryogenesis. Data also suggest that in freshwater fish FAA are an unlikely primary energy substrate during embryogenesis.

Bioassays were carried out with the ‘blue diatom' Haslea ostrearia Simonsen, which is responsible for oyster greening during the fattening period of Crassostrea gigas Thunberg in oyster ponds. Samples of seawater were taken from two oyster ponds: one without oysters and the other with 20 oysters per m[sup2 ], maximal density allowed by the French AFNOR norm for ‘refinement'. The aims were to clarify the nutrient requirements of this diatom, also to elucidate the eventual influence of C. gigas at this density on the seawater fertility and to envisage the mass production of this diatom by pond fertilization. Examination of cell numeric densities at the end of bioassays allows us to conclude that silicate was the first limiting nutrient, closely followed by phosphate. Chlorophyll a concentrations led to different conclusions: phosphate was the first limiting factor, but after the seawater storage period in ponds, seawater quality evolved to a deficiency of nitrogen. Silicate addition increased cell division rate, and silicate depletion increased chl a synthesis for this species. Examination of nutrient assimilation ratios confirms that H. ostrearia requires a large amount of silicon. From these results, it was possible to prepare a N + P + Si simplified medium which has been tested in laboratory and field mesocosm conditions. In both conditions, similar results were observed: a significant increase in H. ostrearia cell concentrations and consequently an evolution up to the greening stage. Applications of this work are numerous; the principal permits us to envisage the production of this species in 25-m3 ponds, with the aim of allowing constant production of the greening phenomenon.

Le banc ostréicole de Ronce (175 ha) au sud du bassin deMarennes-Oléron (France) constitue un site atelier expérimental pourl'étude des mortalités estivales de l'huître creuse Crassostreagigas. En 1997, la croissance, la maturité sexuelle, la survie etl'environnement des élevages à plat et sur tables sont comparés surquinze sites expérimentaux. En 7 mois, le taux de mortalité desélevages à plat atteint 23−33 % contre 8−19 % pour les élevages surtables. La mortalité varie avec la saison. Elle s'intensifie avec latempérature, en période de pré-ponte et de catabolisme duglycogène. Des modèles statistiques de production de chair sèche del'huître sont établis selon la latitude de la longitude des sites. Cesmodèles (en poids sec) sont orientés nord - nord-ouest et montrent que ladisponibilité alimentaire pour les cheptels d'huîtres, diminueprogressivement du large vers le fond de la baie. Les rendements biologiques (poidstotal), sont compris entre 85 et 2 %, respectivement pour des sites sur tables à25 et 50 % d'exondation. Pour les élevages à plat, une perte de productionsupérieure à 10 % est enregistrée dans certains parcs du sud dubassin. Les meilleurs sites, à 50 % de production (poids total), sontsitués dans la partie est - nord-est du banc de Ronce.

Escapement through the body or under the footrope of the sampling trawl used for the Mediterranean international trawl survey programme (MEDITS) was assessed i) by means of visual observations performed with a towed operating vehicle equipped with a high-sensitivity video camera, and ii) by attaching small bags to the outside of the trawl body and under the footrope. Due to the small size of most of the individuals present in the study area and to the towing speed, fish behaviour in front of the trawl could not be frequently observed. In contrast, their behaviour was easily observed inside the net, especially upstream and inside the codend. Some species, such as horse mackerel (Trachurus sp.), showed greater swimming endurance compared with others such as annular seabream (Diplodus annularis). In three fishing trips conducted in different seasons in 1996 and 1997 to obtain data on several species in different areas of the Adriatic, six small net bags were mounted outside the body of the MEDITS trawl to quantify escapement through the trawl belly and under the footrope. Significant escapement of many species occurred in the near-bottom part of the side panels. Norway lobster (Nephrops norvegicus) had the highest rate (64 %), mainly represented by small-size individuals. The escapement of greater forkbeard (Phycis blennoides) was also high (53 %). For hake (Merluccius merluccius), common pandora (Pagellus erythrinus) and poor cod (Trisopterus minutus capelanus), rates ranged from 10 to 16 %. The escapement of red mullet (Mullus barbatus) was very low despite their great abundance. Blue whiting (Micromesistius poutassou) escaped mainly through the mid-height part of the side panel. This great variability of escapement values could affect the proportion rates of the species sampled during a standard survey. Different escape behaviours among size classes were observed for M. poutassou, T. minutus capelanus and P. erythrinus, with smaller individuals tending to escape towards the bottom and larger ones towards the higher parts of the trawl body. In the species where the escape rate was size-dependent, therefore, the size-frequency distributions obtained from the codend catch may not reflect actual size-frequency distributions.

Haemocytes of Mytilus edulis, allowed to attach to the plastic surface of a tissue culture plate in the presence of haemolymph, were observed by time-lapse video recording. When bacteria were added at concentrations of 10 or 50 bacteria per haemocyte, certain bacterial strains caused rounding of the cells within 2–3 h. Haemolymph was necessary for the rounding to occur; if bacteria were added in sterile seawater there was no significant difference in the number of rounded cells between control and bacteria-treated cultures for up to 4 h. The haemolymph factor required for this activity was active at 1/64 dilution in seawater, was sensitive to trypsin treatment, and activity was halved on heating at 56 or 100 °C for 30 min. For the most toxic bacteria tested, Vibrio alginolyticus NCMB 1339 and Vibrio anguillarum A7, haemocyte cell rounding appeared to be induced by a very small number of bacterial cells. Bacteria-free culture supernatant of V. anguillarum 2981 induced rounding of haemocytes in a dose-dependent manner, with 50 % of cells being rounded at a dilution of approximately 1/500 of the culture supernatant. In a survey of 226 bacterial isolates, those isolated from incidents of disease in a bivalve hatchery were significantly more toxic towards haemocytes than bacteria isolated from hatcheries without disease or from turbot hatcheries.

A population of leaping grey mullet Liza saliens was studied in order to test whether growth rates decrease in summer owing to a reduction in food quality. A total of 330 juveniles of the 2-year age group were collected for measuring monthly changes in standard length, total weight, length growth rate and weight growth rate. Another 160 fish of the same age were caught monthly in February, April, August and November to measure food quality and calculate energy intake. Food quality changed as predicted. The organic matter content of the diet on a dry matter basis was 9.7% in April, 7.9% in August and 11.7% in November. The protein content of the diet on a dry matter basis was 9.0% in April, 6.4% in August and 9.3% in November. The carbohydrate content of the diet on a dry matter basis was 0.6% in April, 0.7% in August and 1.8% in November. The lipid content of the diet on a dry matter basis was 0.2% in April, 0.2% in August and 0.6% in November. The energy content of the diet was 2.63 kJ·g−1 in April, 2.21 kJ·g−1 in August and 3.13 kJ·g−1 in November. All the analysed mullet stomachs were empty in February, which suggests that they starve in winter. Daily rations increased when food quality decreased (4% of body weight in April, 6% in August and 1.4% in November). This allowed mullet to show high growth rates from June to August and to overcome a possible food limitation in the warm season. However, we do not know whether they would have grown even faster if food with a higher quality had been available.

Both in Indonesia and Vietnam, larval rearing of Pangasius hypophthalmus remains problematic due to the variable and generally low survival rates obtained. The first week represents the most critical period for these larvae and up to now, cannibalistic behaviour was considered as the main cause of mortality. In the present study, two experiments were carried out in order to better understand the evolution and causes of mortality of P. hypophthalmus larvae from hatching up to 8 d of age and to find measures to improve survival rates. The first experiment was designed to evaluate the importance of cannibalism and differences in mortality when larvae from two different females were reared either in groups of 30 individuals or in isolated condition (30 larvae reared separately). In both cases, the culture was carried out either with or without antibiotic. The aim of the second experiment was to test oxytetracycline and different disinfectants (chloramine-T, formalin and ‘formalin + malachite green oxalate’) at different dosages in order to prevent bacterial outbreaks in the culture. The results indicated that the survival rates of P. hypophthalmus larvae was dependent on the initial quality of larvae or eggs and that larval mortality was more a consequence of pathogenic infection than a direct effect of cannibalism. The present study demonstrated that the survival rates of larvae were systematically improved when rearing was carried out in water containing antibiotic (oxytetracycline at a dose of 5 to 20 mg·L−1). Survival rate and final mean body weight of larvae as high as those obtained using antibiotic were also reached with applications of disinfectants such as chloramine-T and formalin. The use of these disinfectants is recommended for commercial P. hypophthalmus hatcheries.

Techniques were developed for labelling prey, and for gut content analysis in fish larvae. Labelling consisted of a short feeding period of the prey (rotifer and Artemia metanauplii) on black-drawing ink before supplying them to the larvae. Prey labelling was rapid and remained stable for at least 3 h when transferred into seawater. In addition, a method was tested to facilitate the observation of larval gut contents. The method, based on Dawson's technique, involved fixation, removal of lipids and clearance of turbot (Psetta maxima) larvae, which become transparent and ready for gut content analysis. This treatment did not interfere with the black ink label of the ingested prey.

Respiration rates of various geographical strains of Crassostrea gigas were compared to assess the respiratory expenditure as a physiological indicator of catabolism (cost of maintenance). Parental oysters, sampled in France (Marennes-Oléron), Japan (Hiroshima), Taiwan (Tunkang) and Spain (Cadix), were differentiated by both their geographic origin and by mitochondrial DNA markers, allowing the distinction between the two closely related taxa Crassostrea gigas and Crassostrea angulata. After reproduction of these parental oysters, respiration rates of spat of each strain, reared under common controlled conditions, were individually estimated at 20 °C by using a volumetric microrespirometer. Our results demonstrated that physiological variability existed among the Crassostrea gigas strains and is likely to be related to physiological differences between geographical regions and/or genetic adaptations. The French strain showed the highest rates (0.71 μL·h−1), while the Japanese, Taiwanese and the hybrid between Spanish and French strains consumed less, 0.53, 0.43 and 0.40 μL·h−1, respectively. Our results confirmed the discrepancies previously suggested between Crassostrea gigas and Crassostrea angulata. Comprehensive physiological assessments should be carried out over a wide temperature range to confirm our results and to further evaluate growth potential. Appropriate decision making based on these studies will help future shellfish management in shellfish rearing areas such as the overstocked Marennes-Oléron Bay.

Manila clam (Tapes philippinarum) culture and sediment interactions were tested by comparing two rearing areas, including an oceanic (‘Le-Ferret’) and a more estuarine (‘Les-Jacquets’) sites in the bay of Arcachon (France). The growth of a calibrated clam population (10-mm spat) was monitored in these two areas with a concomitant sediment-water interface survey over a 1.5-year period. Two sites per area, including control and rearing plots, were sampled on a monthly basis. The potential clam farming impacts by bioturbation and interactions were examined at three sediment depths: 0−1, 1−2 and 2−10 cm. Moreover, the main hydrobiological parameters were measured on a weekly basis to establish a relationship between these parameters and sediment-water interface characteristics. The existence of a gradient between the three depths was revealed for most of the parameters examined, with the exception of silt and organic carbon levels, and this regardless of the area examined. Clam growth showed a rate improvement in the oceanic area, which is characterized by a lower silt content. The clam effect was minimal and the activity identified at the ‘Ferret’ site was in fact due to the presence of a net which acted as a particle trap. No significant relationship was established between water column parameters and those of the sediment-water interface at the two geographical sites examined. These results demonstrate that clam rearing had only a limited effect on the environmental sediment parameters (i.e. water percentage, and phaeopigments and silt levels) from a spatio-temporal point of view. Therefore, a return to environmental conditions existing before the implementation of clam farming is likely to occur upon cessation of this activity.

Changes in the fatty acid profiles of the Percichthyid fish trout cod, Maccullochella macquariensis (Cuvier), and Murray cod, M. peelii peelii (Mitchell), two Australian native freshwater fish species, were investigated during early development from egg to yolk-sac-resorbed larval stage. In the two Percichthyid fishes polyunsaturated fatty acids (PUFA) accounted for more than 50 % of the 19 quantified fatty acids in total lipid. The fatty acids that occurred in the highest abundance in both trout cod and Murray cod, in all developmental stages, in order, were docosahexaenoic acid [DHA 22:6(n-3)], arachidonic acid [AA 20:4(n-6)], oleic acid [18:1(n-9)] and palmitic acid (16:0), all of which exceeded 100 μg per mg total lipid in most instances. The ratio of 22:6(n-3) to eicosapentaenoic acid-20:5(n-3) in eggs of trout cod and Murray cod was 5.4:1 and 7.3:1, respectively, and remained almost unchanged through development, and was considerably higher than the 2:1 ratio generally reported for fish eggs. In trout cod, 11 of the 19 fatty acids in total lipid decreased during the transformation from egg to yolk-sac-resorbed larva. In Murray cod, only 16:1(n-7) showed a significant decrease whilst 20:4(n-6) increased significantly with development. Overall, there was a tendency in both species to conserve n-3 and n-6 series highly unsaturated fatty acids (HUFA), suggesting their essentiality in first feeding larvae. These observations are discussed in relation to the feeding habits of trout cod and Murray cod, which are top order, freshwater carnivores.

Observations were made in Senegal between 1997−1998 on the length of embryonic development in Octopus vulgaris. The data were from eggs which had been laid by two females in the open sea and fourteen females in concrete tanks. The observations in natural surroundings are the first concerning this species. Hatching occurred after 15−42 d at 27 °C, 29−49 d at 22−23 °C, 57−65 d at 21 °C and 80−87 d at 17 °C. These values are higher than the few data previously recorded in European aquariums, particularly for temperatures under 20 °C.

An experiment was carried out to evaluate the effects of brine shrimp nauplii (Artemia sp.), Cladocera (Moina sp.), Tubifex worms and a trout starter diet on growth performances and survival rate of Mekong catfish larvae (Pangasius bocourti Sauvage, 1880). Larvae accepted all four types of experimental diets, owing to large mouth opening at the first feeding (0.6–1.0 mm at 45° and 90° mouth opening, respectively). Artemia nauplii and Tubifex worms resulted in the same growth performances and survival rates for a 9-d nursing time with specific growth rates of 36–37 %·d−1 and survival rates of 92–93 %. Moina led to a lower growth performance (31 %·d−1) but the survival rate (94 %) was not significantly different to that of larvae fed Artemia nauplii or Tubifex worms. Trout starter feed, dry pellet, proved relatively less suitable for larval rearing of P. bocourti owing to a low survival rate (68 %) and growth performance (21 %·d−1). The study confirmed the feasibility of completely replacing Artemia nauplii by Tubifex worms.

The impact of Mediterranean mussels (Mytilus galloprovincialis Lamarck) on particle removal from the water column under different flow velocities was measured in the laboratory within a recirculating flume. At 20 °C, the filtration rates increased with current velocity up to 20−25 cm·s−1. Filtration rates remained the same at 26 °C. At high phytoplankton concentration (Cryptophyceae: 8 500−11 000 Cryptomonas sp. cells·mL−1), filtration rates were low (0.2−0.4 L·h−1 per standard individual of 1 g dry weight), whereas higher filtration rates (0.5−2.5 L·h−1 per standard individual) were observed with lower concentrations of the algae Prorocentrum minimum (Dinophyceae : 1 300−5 800 cells·mL−1). The filtration rates of M. galloprovincialis were affected by high phytoplankton loads, and exhibited a maximum related to current velocity. Our results suggest that mussels, feeding over a wide range of seston concentrations and flow velocities, show an adaptive behaviour in an area where environmental conditions are known to vary drastically.

The objective of this study was to investigate the impact of cadmium on the structure of gills and epipodites in late juvenile Penaeus japonicus. Cadmium titrations were performed by atomic absorption flame spectrophotometry, and structural observations were performed through light- and electron-microscopy. The cadmium concentration increased in different tissues (mainly gills, epipodites and hepatopancreas) according to the external cadmium concentration and the exposure time. The structural changes which occurred in the gill and epipodite cells appeared to be a function of cadmium accumulation in these tissues. Gill cells of shrimps exposed to 2 and 200 μg Cd·L−1 for 15 d did not display discernible structural changes. An increased number of nephrocytes was noted in gill filaments of shrimps exposed to 200 μg Cd·L−1. Exposure to 2 000 and 4 000 μg Cd·L−1 during 4 d resulted in profound structural changes. The epithelial cells were necrosed, disorganized and vacuolized. Exposure to 2 μg Cd·L−1 for 15 d did not result in discernible structural changes of epitodite cells. Exposure to 200 μg Cd·L−1 for 15 d, 2 000 and 4 000 μg Cd·L−1 during 4 d induced profound alterations of the epipodites: increased thickness, decreased number of apical microvilli, basal infoldings and mitochondria, occurrence of pseudomyelinic structures. These alterations are discussed in relation to the respiratory and osmoregulatory functions of gills and epipodites.

The technique already adopted by the authors for the cryopreservation of rainbow trout blastomeres was applied to carp. Three stages were utilised for cell freezing: the morula stage, the early blastula stage and the late blastula stage. Survival rates were 89 ± 1.6 % for morula cells, 94 ± 0.6 % for early blastula cells and 96 ± 0.4 % for late blastula cells. Early blastula and late blastula cells reaggregated into morula-like bodies within 2 h in culture medium. Results suggest that the freezing technique adopted for rainbow trout may be successfully applied to carp. The morula stage blastomeres were more sensitive to freezing than blastula stage blastomeres, as already found in rainbow trout.

Des paramètres de la reproduction d'une population isolée du tilapia Sarotherodon melanotheron ont été étudiés durant 2 années consécutives et comparés avec les données de la littérature obtenues sur des populations vivant dans son milieu naturel. Le sexe-ratio (année 1 : 1:2,69; année 2 : 1:1,96) en faveur des femelles varie de façon saisonnière. Les mâles atteignent la maturitésexuelle plus rapidement (année 1 : 129 mm LS ; année 2 : 126 mm LS) queles femelles (année 1 : 135 mm ; année 2 : 136 mm LS). Le cycle dematuration des gonades est continu. Ces résultats sont dans l'ensemblesemblables à ceux obtenus dans le milieu naturel de l'espèce. Cependant,une fécondité inférieure et un diamètre ovocytaire plus grandsont notés dans le lac d'Ayamé. Le facteur de condition moyen despopulations du lac, intermédiaire entre des valeurs observées dans lesmilieux lagunaires, indique une bonne adaptation de l'espèce aux conditionsd'eau douce du lac.

The relationship of size to MEP-2* genotype was investigated in 0+ juvenile Atlantic salmon (Salmo salar) in the River North Esk, Scotland. Significant temperature-associated MEP-2* heterogeneity was observed among tributaries and, in the two tributaries studied, size and MEP-2* genotype were significantly associated. No size association, or heterogeneity among tributaries, was found for the other allozyme polymorphisms screened. The results suggest that the association between size and MEP-2* variation, noted by others, is likely to be widespread in wild populations, and potentially linked to habitat temperature.