This paper analyses the population dynamics, growth and feeding ecology of Dicentrarchus labrax in order to gain a better understanding of its present role in the western Dutch Wadden Sea ecosystem. Otolith analysis showed that the population is mostly comprised of individuals aged 3–5 years old and between 20 and 45 cm in length. In autumn, 0-group juveniles are also an important part of the population. Both juveniles and adults use the area as a feeding ground exhibiting an opportunistic feeding strategy that relies on available prey, especially the brown shrimp Crangon crangon. Stomach content analysis and nitrogen stable isotope analysis showed an ontogenetic shift towards piscivory and a general decrease in the dominance of invertebrates with increasing size. Over the last 50 years, large between-year fluctuations in D. labrax abundance have been observed with an underlying increasing trend from about 1990 until 2007 followed by a subsequent decline. Spring abundance showed significant relationships with temperature and salinity while autumn abundance was only related to temperature. Spring and autumn D. labrax abundance were also strongly related to abundance of brown shrimp C. crangon prey. Long-term trends in temperature and salinity in the area suggest that environmental conditions for juvenile growth have become optimal, resulting in increased abundance since the mid-1980s. Continued monitoring of the dynamics of this species in the Dutch Wadden Sea is important to understand and anticipate the effects of climate change on the D. labrax population and its role in the local food web.

Inter- and intraspecific crossbreeding experiments were conducted to evaluate the aquaculture potential of hybrids in the genus Dicentrarchus, focusing on fertilisation and hatching success. The experimental design consisted of 24 controlled crosses in which individual and pooled fertilisations were made between wild D. labrax individuals (8 dams and 5 sires originating from West Mediterranean and Atlantic populations) and wild D. punctatus (6 sires). Three experiments were successively performed: (1) dams from the Mediterranean population, individually considered to have good egg quality, (2) dams from Mediterranean population, individually considered to have poor egg quality and (3) crossbreeding using pooled eggs from the Atlantic population. In each case, batches of these eggs were fertilized by sperm from males of the two species. Sperm cell quality (concentration and motility) was verified before experimentation in all cases and equal numbers of sperm cells from each male were used to individually (without inter-sire competition) fertilise egg batches. Through the repeated artificial crosses between female common sea bass Dicentrarchus labrax (Linnaeus 1758) and male spotted sea bass D. punctatus (Block 1792), these experiments showed that no post-zygotic reproductive barriers exist to interspecific hybridisation between these two species when using D. labrax as dams and D. punctatus as sires. Phenotypically, the F1 hybrids were easily recognisable: they inherited the characteristic black spots of D. punctatus. Furthermore, embryo survival was significantly higher in interspecific crosses compared with intraspecific controls, showing increased fitness for this trait (increased performance at early life stage). Then, the experimental breeding design validates the observation that West Mediterranean and Atlantic common sea bass populations are different. Indeed, the inter-population crosses (between West Mediterranean dams and Atlantic sires) also revealed increased fitness at early life stages in comparison with the progeny of intra-Atlantic population crosses. However, these individuals were still smaller than their interspecific counterparts. The ability to produce viable F1 hybrids will have significant implications for the practical improvement of sea bass aquaculture.

Reared sea bass were submitted to six stressful situations: hyperoxia with or without hypercapnia, increased stocking density in an open flow or recirculating system, transfer to another tank and nodavirus injection. The potentially negative impact of these factors on the lives of sea bass was investigated by measuring 9 water parameters and 19 fish parameters including total serum protein (TSP). TSP has already been used to evaluate stress. The present study investigates data of previous and new experiments, concentrating on the potential use of TSP as a routine indicator to assess welfare in sea bass reared on fish farms. In the current experiment, oxygen and carbon dioxide were seen to affect levels of TSP, but alterations were too erratic to enable proper comparison, probably because they are normal components of the fish environment and become toxic only by dose increase. TSP decreased when stocking density increased. After transfer to another tank, TSP decreased to 14% for three weeks and then increased during the fourth week through compensative overproduction, before returning to normal levels after 2 months. The results confirmed that transfer is an important stress factor for fish, with cumulative effects for successive transfers. TSP alteration of nodavirus-injected fish depends on the type of symptoms, which can be divided into 3 groups: (i) dying fish, in which TSP increased sharply due to over-production of protein involved in non-specific defences and inflammation, then decreased dramatically before death; (ii) whirling fish, a group that included both fish that later died, in which TSP decreased, and fish that subsequently survived, in which TSP increased due to development of specific immunity; and (iii) asymptomatic fish, in which TPS was similar to control levels and which were probably insensitive to nodavirus and/or had developed defences. In this paper, different mechanisms of TSP alteration are proposed and the interest of TSP as a field parameter is discussed. TSP is a non-destructive parameter that is robust, easy to measure everywhere and cheap, representing a suitable way of monitoring the overall welfare of fish by its regular increase. It can be used only as a “warning” of poor rearing conditions, however, and further investigations would be needed to identify the specific stress or health disorder.

Recirculation aquaculture system (RAS) is the type of land-based aquaculture productionthat interferes the least with the environment, particularly due to low effluent volumeand overall water requirement. Water reuse, sometimes limited by the accumulation of wasteproducts excreted by fish, can be improved by incorporating another biotechnical componentin the form of high rate algal pond (RAS+HRAP), thus adding to the economy and selfsustainability of the system. Our goal was to evaluate whether rearing fish for 1 year ina RAS or RAS+HRAP led to differences in fish production and health, by assessing: (1) fishgrowth; (2) impact on the morphological structure of sea bass target tissues (liver,kidney, and spleen); (3) susceptibility to monogenean parasites; (4) resistance topathogen challenge with Listonella anguillarum; and (5) total bloodprotein. Over the one-year experimental period, sea bass showed no statistical differencesin any parameter evaluated, suggesting that there was a satisfactory purification rate inthe RAS+HRAP system.

During 84 days, the effects of density on juvenile sea bass (Dicentrarchus labrax) (76±16 g) were studied in an experimental tank-based flow through system. Performance, stress response and resistance to virus infection were analysed under five stabilized rearing densities: 10, 20, 40, 70 and 100 kg m-3. Water quality parameters (CO2, total ammonia nitrogen and O2) were measured and maintained close to the recommended values for farmed sea bass by adjusting water renewal exchange. No significant differences were observed between density treatments, neither on stress response (cortisol) nor susceptibility to nodavirus. With regards to biological performances, the daily feed intake and specific growth rate were significantly lower in fish reared at the 100 kg m-3 density. Results on the effects of density in sea bass reared in flow through (present study) and in recirculating aquaculture systems (RAS) (Sammouth et al. 2009) were compared as a contribution to the identification of density not affecting health and welfare in farmed sea bass.

This paper presents a non invasive, rapid and reliable way to quantitatively assess fin erosion in sea bass (Dicentrarchuslabrax). The method is based on a visual assessment of fin profile and area loss of all fins except the anterior dorsal, on a scale from 0 to 4 in comparison with a perfect fin. The effects of stocking density (SD) and temperature on fin damage were investigated under experimental conditions (100–250 g fish). Over a 4-month period, mean erosion index (mean erosion level of all fins) was 10 times higher at 120 than at 20 kg m−3, where most fins were undamaged. Damage was also dependent on time and oxygen concentration (35% lower at 53% O2 saturation than at 105%). Fin condition was also affected by temperature: mean erosion index was 0.22–0.25 at 13–16 °C, but five times higher at 25  °C. Caudal and dorsal fins were always the most eroded. Fin damage was then monitored in a large land-based farm using high SD, and in a small sea cage farm operating at low SD. At the first site, 6 batches of two market size groups were examined: L (850–930 g, 50–80 kg m−3) and S (375–400 g, 42–60 kg m−3). Fin condition was good in all batches (mean erosion index, 1.1–1.3) and lowest at the highest SD. At the second site, four batches of large fish (350–890 g, 26–24 kg m−3) and four other groups below market size (100–270 g, 8–16 kg m−3) were examined. Fin erosion was the highest in large fish (mean erosion index, 1.1–1.2) and in the sea cages most exposed to climatic disturbances. In both sites, the most eroded fins were the caudal and dorsal. Differences in other external injuries were also observed between the two sites (less necrosis and more scale injuries in sea cages). The causes of fin damage are discussed in relation to metabolic and/or behavioral adaptations to rearing conditions and the main actions that could be taken to improve fin condition are discussed.

This study aimed at modeling the relative importance of food intake on growth heterogeneity among cultured sea bass (Dicentrarchus labrax). First, we designed an individual growth model comprising five compartments (Energy intake, Losses, Net Energy, Recovered Energy and Maintenance). This model was calibrated with a first experiment carried out in eight tanks; A total of 130 juveniles (11 g) per tank were fed by a self-feeder (84 days, 20°C, 16L : 8D, 30 g NaCl/l). A second experiment was performed to better understand the relation between individual food intake, individual growth and growth heterogeneity, using the model as a tool for a hypothetico-deductive approach on growth heterogeneity (135 passive integrated transponder-tagged fish, same rearing conditions as above and individual food intake measured by X-ray every 14 days). The tested hypotheses were that food intake was (a) homogeneous, (b) proportional to the fish weight (i.e. to W1.00) X-ray (c) proportional to W0.66 and (d) reflected by the X-ray measurements of food intake. For each hypothesis, a simple linear regression between experimental and simulated results was produced. The Fitness indicators of these analyses, together with their confidence intervals (calculated by bootstrapping), allowed testing the relevance of these hypotheses. The analysis indicated that growth heterogeneity was largely accounted for by individual variations of food intake, as revealed by the X-ray analysis, and that food intake was proportional to W1.00, which suggests a dominance hierarchy where small fish are incapable of feeding maximally.

The population dynamics of Sphaerospora dicentrarchi and S. testicularis, myxosporean parasites of sea bass (Dicentrarchus labrax), was studied in different groups of cultured and wild fish. S. dicentrarchi prevalence was higher for wild fish (100%) than for cultured ones (70.5%). Infection levels increased with host age and there were no significant sex differences in cultured fish. Among parasitized organs, the gall bladder and intestine registered the highest infection levels in wild and cultured fish. A progressive increase in infection levels of S. testicularis was observed in cultured males during the spawning season in four consecutive periods. The evolution of the percentage of the different parasitic stages is pointed out. The infection seems to be related to water temperature and gonadal maturation.

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 individual growth variability of passive integrated transponder tagged sea bass was studied using data sets from two different experiments. In experiment 1 (n = 485), fish submitted to different photoperiod regimes were held in fourteen groups of individual weight of 88 ± 13 g (mean ± SD). In experiment 2 (n = 748, initial weight 243 ± 30 g) fish were held in fifteen groups and had either free or restricted access to diets with three lipid levels. After adjustment for treatment and tank effects, individual growth curves were analysed using multivariate analysis (principal component analysis and clustering) and were modelled using the summary statistics technique. Different growth profiles where characterized. All of them appeared to be curvilinear. They differed in their level (initial and final weight), slope (slope, specific growth weight, gain) and especially the ratio of males, which showed sexual growth dimorphism. The fish with similar initial weight proved to have very different growth performances, regardless of the treatment effect. Within the same sex, part of the variability between the growth profiles could be explained by differences in the social interactions and in the genetic potential of growth among individuals.

A sperm cryopreservation protocol adapted from turbot, was tested on sea bass using either 250-μL straws or 1.5-mL cryovials. A dilution to 1/3 in Mounib's extender and a cooling rate of −65 °C·min−1 allowed frozen sperm to recover an initial motility similar to that of fresh sperm at thawing; however, significant differences in motility (P < 0.001, n = 10 fish semen) were observed at further post-activation times, the motility decrease being faster in thawed sperm. At the experimental scale, triplicate inseminations of 2-mL aliquots (approximately 2 000 eggs) showed a significant fertility decay of thawed sperm compared to that of fresh sperm (P < 0.01, n = 12 fish semen) when a discriminating 35·103 spermatozoa to egg ratio was applied. When 70·103 and 200·103 spermatozoa per egg were provided in the same experimental conditions, no significant difference appeared between the fertilisation rates of fresh and thawed sperm. In order to validate the procedure for production or cryobank purpose, a scaled-up protocol was established. Two and 50 mL batches of eggs (approximately 2·103 and 50·103 eggs, respectively) were inseminated in triplicate using either fresh or thawed individual sperms of 5 males with 200·103 spermatozoa per egg. The mean fertility decreased by 23.5 % due to cryopreservation. This decline was explained by the loss of fertility of only one sperm, and only in large-volume conditions, probably due to the delay of use after thawing.

Two groups of sea bass (mean initial weight 78 and 250 g) were given for 23 weeks a commercial diet, whose composition was modified or not (control). The modified diet was: — supplemented with highly oxidized fish oil, — poorly supplemented with ascorbic acid, — not supplemented with butylated hydroxytoluene, DL-alpha-tocopheryl acetate and choline. At the end of the experiment, fish fed the modified diet displayed skeletal muscle degeneration, decreased red blood cell count, haemoglobin content and haematocrit, and increased crythrocyte fragility and plasma enzyme activity (aspartate aminotransferase and creatine kinase). Simultaneously, low DL-alpha-tocopheryl acetate levels and increased amounts of thiobarbituric acid-reactive substances were observed in muscle and liver. On the other hand, growth disorders, liver lesions, changed plasma enzyme activity (alanine aminotransferase, glutathione peroxydase), or altered conjugated dienes in perivisceral fat were not evidenced. The pathological observations were more pronounced on the smaller fish group, but the disease could already be detected by measuring haematological and biochemical criteria, the interest of which in the diagnosis of such nutritional disease is discussed.

This paper concerns eggs of captive fish and gonads of wild fish, from the Brittany coast obtained in the 7-18 °C thermal range. The diameters of eggs, 1.07-1.32 mm are compared to those observed in other areas, especially along the Mediterranean coast. The duration of embryogenesis as a function of temperature and the efficiency of different incubators are discussed. The quality of eggs in relation with larval survival is discussed through the biochemical composition of the eggs collected in captivity compared to that of wild fish gonads. The absolute values of lipids, proteins, fatty acids, lipid classes, phosphatides and minerals measured, also the positive relations obtained between egg dry weight, diameters, mortality during incubation are presented as criteria of egg quality.

This paper describes the large-scale production of eggs and larvae of sea bass (Dicentrarchus labrax) and shows how spawning can be planned to produce viable eggs throughout the year by manipulation of photoperiod and temperature. The rearing temperature was 9.5-22 °C during spawning and 9-24 °C during the gametogenesis. The photoperiodic cycles tested were normal (i. e. the photoperiodic cycle observed at Palavas-les-Flots, mediterranean coast, France, 1984/1987) advanced by 3 to 5 months and delayed by 2 months.