The ability of captive-reared turtles to survive in the wild is not precisely known, nor are movements of immature turtles in the open ocean. To provide information on these issues, a satellite tracking experiment was conducted in the western Indian Ocean to monitor oceanic movements of immature green turtles. Two wild turtles and four captive-reared individuals were tracked. The latter had been displaced after birth from nesting sites to a distant rearing site. Wild turtles survived after release, but did not move far away from release site. We hypothesize that this resident behaviour may be explained by stage-specific habitat requirements. Captive-reared turtles survived after release and migrated over thousands of kilometres. Among these, the oldest immature turtles retrieved the foraging sites of their native population, with movement patterns similar to those displayed by adults. Observed movements may be linked to hydrographic conditions such as general oceanic circulation, sea temperature and thermal fronts.

The histological development of the digestive tract in hatchery-reared green sturgeon (Acipenser medirostris) larvae and the effects of food deprivation on the digestive system organization were studied from hatching until 31 days post-hatching (dph). At hatching, the larval digestive system consisted of two rudiments: a large endodermal yolk sac and a primordial hind-gut. During the endogenous feeding phase, the wall of the yolk sac differentiated into the stomach (glandular and non-glandular regions) and the anterior and intermediate intestine, while the hind-gut primordium differentiated into the spiral valve and rectum. At the onset of exogenous feeding (15 dph at 16 °C), the organization and cytoarchitecture of the digestive system in green sturgeon larvae was generally similar to those of juveniles and adults. Larvae deprived of food exhibited a progressive deterioration, with subtle pathological changes observed after 5-d starvation: shrinkage of digestive epithelia, tissue degeneration, and necrosis were observed at 10–15 d of starvation (30 dph). No changes were observed in the mucous secretion of different regions of the digestive tract of food-deprived larvae. The histological analysis of the larval digestive system may be used to evaluate the nutritional condition of larval green sturgeon in their nursery habitats in spawning rivers, which are affected by dams and flow diversions.

Domesticated/captive stocks and wild/feral populations of common carp from Europe, Central Asia and East/South-East Asia were examined for allozyme (23 populations), microsatellite (11 populations) and mitochondrial DNA (21 populations) variation. Allozyme variability (1.06–1.81 alleles per locus, expected heterozygosity 0.006–0.136 at 16 loci) was much lower than microsatellite variability (2.5–14.0 alleles per locus, expected heterozygosity 0.426–0.887 at four loci). Differences in variability between domesticated/captive stocks and wild-caught ones were more pronounced at microsatellite loci than at allozyme loci, suggesting that microsatellites are better suited to detect population bottlenecks and loss of variation due to inbreeding. All but one European population were fixed for a single composite mtDNA haplotype, which also dominated in Central Asia but was completely missing in East/South-East Asia, indicating a single origin of European carp in Central Asia. All three classes of genetic markers clustered populations into two highly divergent groups: Europe/Central Asia and East/South-East Asia. Hierarchical partition of genetic diversity showed that for microsatellite loci most of variation was due to the within-population component while the highest proportion of mtDNA variation and substantial proportion of allozyme variation was accounted for by differences between geographical regions. Genetic data support the subspecies status of C. c. carpio assigned to the European carp and C. c. haematopterus assigned to the East/South-East Asian carp but do not justify a separate subspecies status (C. c. aralensis) for the Central Asian carp. As demonstrated for a wild/feral carp population from R. Danube, Germany, the genetic markers used in our study may be effectively applied to detect mixing and introgression of intra-species units in the presence of sufficient genetic differentiation.

The chronic effects of exposing sea bass (average initial weight 100 g) to ammonia in water at 22 °C were first evaluated over a 61-day period (period 1, P1) during which nine different groups were submitted to nine ambient ammonia levels ranging from 0.014 to 0.493 mg l–1 NH3-N (0.53–16.11 mg l–1 total ammonia nitrogen (TA-N)) and fed using self-feeders. At the end of P1, the fish were starved for 10 days (P2). Their recovery capacity was tested over 43 days (P3) after which the exogenous ammonia supply was stopped in all treatments and the fish were allowed to feed. After 20 days of exposure a highly significant effect of ammonia was evident from the decrease in feeding activity, voluntary feed intake (VFI) and specific growth rate (SGR), and the increase in the feed conversion ratio (FCR). Ammonia exposure had no effect on circadian feeding rhythm or hourly actuation profiles. At the end of P1, the fish seemed to have adapted to all ambient ammonia concentrations tested since feeding and growth parameters were independent of ammonia levels. But they were unable to compensate for growth losses. Physiological adjustments were observed: plasma TA-N concentrations were positively related to ambient TA-N while there was no major disturbance in plasma urea. Plasma tri-iodo-thyronine concentrations were affected by ambient ammonia concentrations and there were no significant changes in hydromineral balance. During P2, oxygen consumption and urea excretion did appear to have been affected by ambient ammonia. When the exogenous supply of ammonia was stopped (P3), fish exhibited hyperphagia and compensatory growth. In fish previously exposed to the highest ammonia levels, SGR and VFI were highest, and their FCR was improved. At the end of the experiment the final average weights were similar in all of the treatments (range 337–396 g). Depending on the concentrations used, ammonia exposure may enhance subsequent fish appetite and growth rate and have a similar effect on growth performances as restricting feeding level. Within the range tested, no detrimental effect of ammonia on the metabolic capacity of the fish, measured by oxygen consumption and urea excretion, or on their physiological status was recorded, and the fish had a good recovery capacity. In the conditions of the experiment, the non-observable effect concentration (NOEC) was 6 mg l–1.

The fishery for Antarctic krill has been stable for a decade with approximately 100 000 tonnes being caught each year. There is continuing commercial interest in products derived from krill. An examination of patent databases indicates that the development of products for human consumption has been overtaken by the development of aquaculture, pharmaceutical and medical products. The development of products for aquaculture is most likely to be the factor that will drive growth in the krill fishing industry. Management of the Antarctic krill fishery has proceeded in advance of expansion and precautionary catch limits for Antarctic krill currently total 4.89 million tonnes ~50 times the existing harvesting level.

Several molluscs that have been introduced world-wide have become economically important for coastal communities. As far as it is known, at least four scallop species (Argopecten irradians, Argopecten purpuratus, Patinopecten yessoensis, Pecten maximus) have been moved between different biological provinces and it is possible there will be further such movements. Making an introduction involves responsibilities and so requires careful consideration. This is because there have been several unwanted impacts with movements of molluscs in the past. The International Council for the Exploration of the Sea's (ICES) 1995 Code of Practice on the Introductions and Transfers of Marine Organisms and recent revision provides a basis for undertaking such an action wisely. In this review, scallops that may be used in future cultivation or in fisheries as potential candidates are examined in relation to the first phase of an introduction—the prospectus. This prospectus should take account of the purposes and objectives of the introduction, including relevant biological, pathological and ecological conditions in the donor region and the potential impacts of the species in the expected range occupied in the recipient region. This may require a study visit to the donor region to evaluate concerns relating to potential hazards. The ecomorphology of five different scallop shell morphs is discussed in relation to their behaviour and occupied habitat. Such information may provide an indication of their interaction with native scallop species in advance of their introduction.

In aquaculture, a diet both nutritionally sound and organoleptically pleasing is essential to guarantee satisfactory intake. This has not been fully achieved with soleids (Solea solea and Solea senegalensis) because of their special palatability requirements, which are difficult to satisfy with conventional diets. Nevertheless, soleids have long been considered interesting species for aquaculture. To improve the palatability of diets for this family, various substances have been tried. Betaine has been the most effective substance by far, for all the species studied and especially for sole, reporting good results but at too high a cost. In other areas of animal production, the problems of palatability are solved with commercial flavours, which offer scope for specialisation to satisfy the most demanding organoleptic requirements. The aim of the present work is to evaluate the use of a bivalve commercial flavour as an alternative to betaine in sole diets. An ethological methodology, adapted to the feeding behaviour of sole, is developed to qualify and quantify behavioural changes when faced with experimental diets containing either this commercial flavour or betaine. Results show that the commercial flavour externally applied to feed particles performs efficiently as an attractant and as an arrestant, being able to attract the animal to the food source from some distance, provoke the ceasing of locomotion close to the food particle and promote initiation of feeding. In this step of the feeding sequence, it may be considered a viable alternative to betaine from the organoleptic point of view and economic cost. When the commercial flavour is applied internally to the feed, its performance as a stimulant, to encourage the continuation of feeding, is not distinguishable from betaine. Other factors such as time of feeding and size of fish, also assessed in the experiment, boldly influenced the level of acceptation of diets, even more than the composition of the diet itself. The distribution of feed at a time out of the endogenous rhythm of the species provoked a lower feed acceptation. Slight differences in the size of fish also affected the degree of acceptation, this being lower in the smaller fish.

Regular observation of survival of the carp breeding lines constituting a living gene bank at the Institute of Ichthyobiology and Aquaculture in Golysz (Poland) over a period of at least 15 years showed different survival rates for various lines. In this study, we have examined the polymorphism of the major histocompatibility complex (MHC) gene class II B in nine carp lines. The class II B gene encodes for the part of the MHC class II molecule which presents peptides from pathogens and protein antigens that are present in the extracellular milieu and have been taken up into the endocytic vesicles of antigen-presenting cells. Polymerase chain reaction was used to amplify Cyca-DAB gene fragments comprising part of exon 1, complete intron 1 and almost complete exon 2. Exon 2 encodes for the β1 domain which is the most polymorphic fragment of MHC class II molecules. Single-strand conformational polymorphism (SSCP) was applied to detect different MHC class II B haplotypes. The analysis revealed the presence of seven different haplotypes occurring with various frequencies.

Geostatistical conditional simulations are used to get a family of non-smoothed three-dimensional (3D) images of the St. Lawrence krill aggregation from echointegration data at 38 and 120 kHz on a systematic grid of transects. These maps respect the inherent patchiness of krill. Their ensemble gives an histogram of the krill density estimates at any point of the 3D grid, not only the mean density as in kriging. The spatially consistent simulations are conditional to match the observations and their histogram and variogram. The 3D problem is by-passed by transposing to a short series of 2D ones, which simplifies the modelling of the autocorrelation function and has the additional advantage of reducing by a factor of 5 the number of points to simulate. The spatially structured krill density profile is summarised by the first few factors of a principal component analysis, where the variables are the volume backscattering strength at 120 kHz for the integrated vertical bins along the profiles and the observations are the different profiles. The principal component scores are simulated over a 2D-grid and then used to reconstruct the full 3D-image. The method adequately reproduces the histogram, variogram and mean profile of krill density, and cross-validations replicate the observations. It is as precise as an alternative kriging approach to estimate the mean density, but has the additional advantages of requiring less computing time for our particular application. These conditional simulations enable estimating the probability density function of the krill density at any point, an essential information for predator-prey interactions and other ecosystem studies.

In Eurasian perch (Perca fluviatilis), females grow significantly faster than males. Moreover, gonadal development has a significant negative impact on somatic growth and fillet yield. In order to induce sterility, triploidy induction was attempted by subjecting fertilised eggs to heat shocks. Different combinations of temperature (28, 30, 34, 35 and 36 °C), duration (2, 5, 10 and 25 min) and time of shock initiation (TI = 3, 5 and 7 min post-fertilisation) were tested. Flow cytometry analysis was used to assess ploidy level of control and heat-shocked larvae. Low intensity (28–30 °C) and long duration (10 and 25 min) shocks lead to significantly higher survival (44 ± 26%) and triploidisation (71 ± 26%) rates than high intensity (34–36 °C) and short duration (2 and 5 min) shocks (17 ± 19% and 21 ± 26%, respectively). The most effective conditions for efficient triploidy induction were low intensity shock of 30 °C, applied 5 min post-fertilisation for 25 min. This treatment led to the production of all-triploid populations (100%) with up to 43% survival rate.

Although fish have been kept for more than three centuries as ornamentals, and the development of manufactured feed since 50 years ago has contributed to the tremendous growth of this hobby, nutrition of ornamental fish is based on extrapolation of results derived from food fishes under intensive farming conditions. Some research on nutrient (protein, minerals) requirements of growing freshwater ornamental species (live-bearers) in a production environment has been conducted, mainly in Singapore, with emphasis on the provision of live feed during the early stages of the life cycle. Protein requirements varied from around 30% dietary protein for growing omnivorous goldfish (Carassius auratus) to 50% for the carnivorous discus (Symphysodon aequifasciata). Whereas mineral (phosphorus, iron, magnesium, zinc) requirements have received some attention in the guppy (Poecilia reticulata), few researches have concentrated on vitamin requirements of ornamental species. Requirements for fatty acids have been conducted mainly on marine ornamentals (damselfish, seahorses), and accentuated the need for dietary supplementation of n-3 highly unsaturated fatty acids. Fish kept in public and home aquaria presents the problem of diversity of species in the same enclosure, each with its own specific requirements and needs. Maintenance energy levels of ornamental fish varied from 0.068 kJ per day for small neon tetras (Paracheirodon innesi) to 0.51 kJ per day for moonlight gouramis (Trichogaster microlepsis) kept at a water temperature of 26 °C. Research on nutrient requirements of ornamental fish urges for suitable measurements other than only growth rate in order to determine optimal dietary inclusion levels.

This study was designed to specify the testosterone (T), estradiol-17β (E2) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) variations during the pre-ovulatory period in female Eurasian perch, Perca fluviatilis, and also examine the ovarian synthesis of 17,20β-P and 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S). Five females (100–300 g) were collected from a concrete pond from the Lindre Center (Moselle, France) between March and April 1999, three times a week, and sex steroids measured. Two females were also collected from the Lindre pond on three dates (18 February, 14 and 23 March) for an in vitro study. Significant plasma 17,20β-P peaks were measured for the first time in this species reaching 3.5 ng ml–1. However, the synthesis and release of 17,20β-P in blood seems to not be synchronized with the final maturation and ovulation stages. The in vitro study showed that ovaries at the pre-ovulatory stage produce some 17,20β-P but no 20β-S from a tritiated precursor (17-P-3H). 17,20β-P is produced after 30 min and is still present in the medium after 2 h of incubation, but is no longer detectable after 4 h. Some other non-identified compounds were synthesized at this stage suggesting that 17,20β-P was quickly metabolized. Moreover, the plasma level increases, observed in spawned females suggest that this steroid might be involved in the oviposition process. These results suggest a role for 17,20β-P in the final stages of oocyte development.

The size of pelagic fish schools depends on several parameters related to internal factors such as species, number of fish, fish swimming speed and physiological status and to external factors, such as hydrological factors and presence of predators. In order to better understand these relations, results coming from echosounder and multibeam sonar databases are analysed. Field data are collected during four acoustic surveys in the Mediterranean Sea in two different areas (Catalan and Adriatic Seas). The analysis shows differences between the two areas regarding size and position in the water column: schools are deeper and their mean size is lower in the Catalan Sea in comparison with Adriatic Sea. The differences in size of schools are mainly related to differences in school length. Moreover, the elongation of schools seen with the sonar is greater than one and half higher in the Adriatic Sea than in the Catalan Sea, whereas one would expect similar values for the two areas. The results are discussed in terms of environmental influence, avoidance reaction and acoustic capabilities of both tools. A hypothesis is proposed: the variation of school length and consecutively the variation of the correlated dimensions is first related to the strength of the avoidance reaction in front of the vessel and this effect can be reinforced depending on the environmental conditions. The model takes into account the effect of the boat, the vertical constraints undergone by the schools, and the internal requirements of the schools, such as the necessity for fish to keep visual contacts and the cohesion of the group.

Proteases and protease inhibitors were detected in the seminal plasma, blood plasma, skin mucus and spermatozoa. Their molecular weights were estimated using SDS-PAGE under non-reducing conditions. The results demonstrate that the two main bands of anti-proteinase activity (APA) detected earlier in common carp seminal plasma with molecular weight of approximately 47 and 58 kDa are also present in other fluids. The intensity of staining was highest in blood and seminal plasma. The intensity in skin mucus was visible, but in a sperm extract it was faint. An additional fast migrating band (30 kDa) was observed only in seminal plasma. Highest APA was found in blood and seminal plasma followed by skin mucus. The activity in sperm extracts was low. The two serine-like proteases with molecular weight of 79 and 189 kDa in seminal and blood plasma have also been found. In skin mucus, protease of 79 kDa was also present. Metalloproteinases with molecular weights of 61 and 69 kDa were found in seminal and blood plasma but metalloproteinases of 44 and 38 kDa were observed only in seminal plasma. Although metalloproteinases, of molecular weight ranging between 61 and 75 kDa, were also visible in a sperm extract, the experimental approach used in this study did not allow unequivocal identification of unique proteases of spermatozoa. Blood plasma contains a serine protease and protease inhibitor not present in seminal plasma. Skin mucus also showed the profile of three unique proteases (two EDTA stimulated and one metalloproteinase). These results indicate that the analysis of proteases and their inhibitors makes it possible to distinguish contamination of milt with either blood or skin mucus. The physiological role of the detected protease-inhibitory system in fish seminal plasma is still unknown. It is possible that the protease inhibitor and proteases, unique for seminal plasma, are involved in a specific function of milt or testis (e.g. the control of spermatogenesis).

Among the gastropods, some muricid shells are composed of an inner aragonitic crossed lamellar layer and a calcitic prismatic outer layer. The analysis of the structure and composition of the two layers of Concholepas shows that the crossed lamellar layer is similar to those of other Mollusc taxa. Sr, Mg and S contents are low in both layers. According to infrared spectrometry, the organic content of the outer calcitic layer is higher than that of the aragonitic crossed lamellar layer. The study of the nanostructure allows for the proposal of a new 3D interpretation of the fine structure of the crossed lamellar layer. The calcitic prismatic layer is compared with the outer calcitic prismatic layer of an archaeogastropod genus: Haliotis.

Echosounder data from four surveys (1992, 1993, 1995 and 1996) is used to investigate the spatio-temporal variability of school behaviour in North-Western Mediterranean waters. The schools are described using morphological, energetic, spatial and temporal descriptors. The variability in the morphological, positional and energetic parameters of the schools is attributable more to the size of the school's individuals (juveniles or adults) than to the relative composition (percentage) of pelagic species in the area. This fact made difficult the identification of species in the studied area. The concentration of schools in certain geographic zones is determined by local oceanographic characteristics that favour the trophic or reproductive activity of these species. The diurnal aggregative behaviour of pelagic species is typical of the zone and no schools were detected at night. The biomass of the pelagic species in the area under consideration has diminished during the 4-year study period and no relationship was found between the number of schools and the biomass evaluated. This is the first time that the schools of small pelagic fishes from the Spanish Mediterranean Sea have been described and the information could be useful to the management and exploitation of the fisheries in the area.

The fisheries of Lake Victoria in East Africa must be managed effectively to ensure sustainable food supplies. This has been impossible in the past due to inadequate knowledge of commercially important fish stocks. Here we present the first acoustic abundance estimates of fish in Lake Victoria. Five lakewide acoustic surveys were conducted between 1999 and 2001, using the Simrad EY500 echo-integrator with a 120 kHz split-beam transducer. There are many species of fish in Lake Victoria, however, only limited identification of targets can be achieved by present methods. Broad categories were distinguished by visual examination of echo-traces. The echo-integrals were partitioned between four target groups: (1) the Nile perch (Lates niloticus), a top predator, (2) small pelagics comprising mainly the dagaa Rastrineobola argentea together with mixed species of haplochromines, (3) the crustacean Caridina nilotica and (4) other species. Spatial and temporal differences in the Standing Crop were observed between north and south, and between shallow and deep water. Most fish were found inshore but the spatial distribution varied between seasons. Mid-lake fish densities were higher in August compared to February. In August, the water column is well mixed while in February it is stratified with a low-oxygen layer inhospitable to fish near the bottom. There are consequent changes in the characteristics of observed echo-traces. Over the survey series, Nile perch biomass showed a consistent decline, while the stocks of small pelagic species increased. We emphasize the need for simple rules to identify species, and hydrographic monitoring to assist echo-trace classification. In the absence of any other source of comprehensive biomass estimates, the value of acoustic surveying in Lake Victoria is demonstrated.

Starting microalgae continuous culture generally includes a preliminary batch culture to obtain sufficient cell density. It is possible to apply continuous regime from the beginning of the culture (IC mode) rather than to begin by an initial batch (IB mode). It is our purpose to check that both initial modes lead to identical steady-state cell characteristics. The microalga Isochrysis galbana affinis Tahiti was used for this comparative study. With an initial cell density of 5 × 105 cell ml–1 and a dilution rate of about 1.0 d–1, both IB and IC modes led to identical cell density once steady-state is reached between 6 and 8 d after inoculation in the two cases. Cell concentration of chlorophyll a and pheopigment a were found to be similar for IB and IC modes at steady-state. Initial culture conditions did not influence saturation irradiance and oxygen consumption rate, which were found to be 650 ± 143 μmol phot m–2 s–1 and 1.54 × 10–3 ± 10–5 μmol O2 ml–1 min–1, respectively. At steady-state, nutrient cell uptakes were ρN = 83.3 ± 2.0 fmol N cell–1 d–1 for NO3– and ρP = 5.5 ± 0.4 fmol P cell–1 d–1 for H2PO4– and did not exhibit significant differences between IB and IC modes. Under the prevailing experimental conditions, results show that IC mode involved very similar steady-state cell characteristics when compared to IB mode subsequent steady-state. IC mode could be an attractive alternative especially for experimental laboratory studies, as it should lead to higher flexibility in starting continuous cultures.

The exposure of freshly spawned, immotile carp sperm to hypoosmotic media triggers the initiation of calcium-dependent flagellar motility. Intracellular calcium concentration has been thought to be the critical component in motility initiation, possibly acting through a novel signalling pathway. The sensitivity of sperm cells to changes of osmolality of the environment raises the question whether a mechanoregulated osmosensitive calcium pathway is involved in the activation mechanism of carp sperm motility. The sperm cells are in a depolarized state in the seminal plasma (Ψ = –2.6 ± 3 mV) and they hyperpolarize upon hypoosmosis-induced activation of motility (Ψ = –29 ± 4 mV). The intracellular sodium [Na+]i, potassium [K+]i and calcium [Ca2+]i ion concentrations were determined in quiescent cells, and at 20, 60 and 300 s after activation. The [Na+]i and [K+]i of the quiescent cells were similar to the [Na+]e and [K+]e of the seminal plasma. Following hypoosmotic shock-induced motility, both [Na+]i and [K+]i decreased to one-fourth of the initial concentration. The [Ca2+]i doubled at initiation of the motility of the sperm cells and remained unchanged for 5 min. Bepridil (50–250 μM), a blocker of the Na+/Ca2+ exchanger, blocked carp sperm motility reversibly. Gadolinium, a blocker of stretch-activated channels (10–20 μM), inhibited sperm motility in a dose-dependent manner and its effect was reversible. Hypoosmotic shock fluidized the membrane and gadolinium treatment made it more rigid in both quiescent cells and hypotonic shock treated but immotile sperm cells. Based on these observations, it is suggested that, besides the well-known function of potassium and calcium channels, stretch-induced conformational changes of membrane proteins are also involved in the sperm activation mechanism of common carp.

Hydroacoustical estimation of fish abundance and distribution is performed in three reservoirs that are characterised by different levels of eutrophication. The Biosonics 101 dual beam echosounder with a frequency of 420 kHz and the ESP software for acoustical data analyses are used. A clear dependence between fish density and the level of eutrophication is observed. In the mesotrophic Solina reservoir, fish abundance is over an order of magnitude lower than that in the eutrophic Dobczyce and Sulejów reservoirs. Fish length distributions have different shapes in the three reservoirs, which indicates the changes in fish size structure due to eutrophication; however, the mean target strength of fish does not differ significantly. These results suggest that hydroacoustically collected data may help to assess the ecological state of inland waters and may be used together with other methods in monitoring the water quality.