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In mariculture facilities, bacterial infections pose significant production challenges, with potentially catastrophic impacts on fish species. Bacterial co-infections are a widespread phenomenon in the natural marine environment, although their impact on aquatic organisms remains poorly investigated. This study aimed to detail the pathological findings associated with a natural bacterial co-infection caused by three different pathogens, namely Photobacterium damselae subsp. piscicida, Tenacibaculum maritimum and Vibrio sp., as the cause of mass mortality in European sea bass. The fish had been reared in open-net cages in Sicily and later transferred for experimental research purposes to a user establishment after immunization with an inactivated vaccine. Macroscopic, cytological and histopathological examinations were performed on 109 animals, and bacterial species were identified by the 16S rRNA gene. Overall, ulcerative skin lesions, necrotizing myositis and tail rot with occasional tail loss were associated with tenacibaculosis and vibriosis, while P. damselae subsp. piscicida mainly caused granulomatous inflammation in the spleen and head kidney. Finally, an injection site reaction due to the oil-adjuvanted vaccine administered intraperitoneally was observed in the abdominal fat. Understanding the impact of bacterial pathogens is essential to manage the health and welfare of farmed fish, and the importance of a good health monitoring program cannot be overstated to avoid outbreaks and the possible emergence of new pathogens due to the intensification of the production systems, antibiotic resistance and climate changes. The study would also highlight the importance of the quarantine period when animals supplied for research come from aquaculture farms and how the main goal in the near future should be to better define the procedures to provide completely pathogen-free animals. [ABSTRACT FROM AUTHOR]

In mariculture facilities, bacterial infections pose significant production challenges, with potentially catastrophic impacts on fish species. Bacterial co-infections are a widespread phenomenon in the natural marine environment, although their impact on aquatic organisms remains poorly investigated. This study aimed to detail the pathological findings associated with a natural bacterial co-infection caused by three different pathogens, namely Photobacterium damselae subsp. piscicida, Tenacibaculum maritimum and Vibrio sp., as the cause of mass mortality in European sea bass. The fish had been reared in open-net cages in Sicily and later transferred for experimental research purposes to a user establishment after immunization with an inactivated vaccine. Macroscopic, cytological and histopathological examinations were performed on 109 animals, and bacterial species were identified by the 16S rRNA gene. Overall, ulcerative skin lesions, necrotizing myositis and tail rot with occasional tail loss were associated with tenacibaculosis and vibriosis, while P. damselae subsp. piscicida mainly caused granulomatous inflammation in the spleen and head kidney. Finally, an injection site reaction due to the oil-adjuvanted vaccine administered intraperitoneally was observed in the abdominal fat. Understanding the impact of bacterial pathogens is essential to manage the health and welfare of farmed fish, and the importance of a good health monitoring program cannot be overstated to avoid outbreaks and the possible emergence of new pathogens due to the intensification of the production systems, antibiotic resistance and climate changes. The study would also highlight the importance of the quarantine period when animals supplied for research come from aquaculture farms and how the main goal in the near future should be to better define the procedures to provide completely pathogen-free animals.

Year class strength is an important determinant of fish population size, but the drivers are often unknown. The northern stock of European sea bass (Dicentrarchus labrax) is an important target species for both commercial and recreational fisheries. Scientific assessments showed a rapid decline in spawning stock biomass from 2010-18 attributed to a combination of fishing mortality and poor year class strength. Recruitment to the adult stock is linked to the abundance and temporal dynamics of young bass in estuarine nursery areas, but little is known about the relative importance of environmental and biological drivers on the survival of these young life stages. In this study, we use Generalised Linear Models to attempt to identify important local environmental (sea surface temperature and river flow) and biological (chlorophyll-a concentration and predator abundance) drivers of young sea bass abundance. We focus on seven British and Irish estuarine areas that are important to the northern stock of European sea bass. In four English estuarine areas there were good model fits to the abundance of young sea bass, but predictors differed amongst these suggesting that drivers of abundance may differ among individual nursery areas. This was further demonstrated by poor fits of models generated for English estuaries to interannual patterns of abundance in the Irish nursery areas tested. The differences found in the most important abundance drivers amongst areas highlight the complex and differing dynamics between estuaries. If the number of young bass that eventually join the adult stock is dependent on survivors from a diverse set of unique nursery area conditions, then endeavours to incorporate this knowledge into fisheries management should be further explored. [ABSTRACT FROM AUTHOR]

Year class strength is an important determinant of fish population size, but the drivers are often unknown. The northern stock of European sea bass (Dicentrarchus labrax) is an important target species for both commercial and recreational fisheries. Scientific assessments showed a rapid decline in spawning stock biomass from 2010-18 attributed to a combination of fishing mortality and poor year class strength. Recruitment to the adult stock is linked to the abundance and temporal dynamics of young bass in estuarine nursery areas, but little is known about the relative importance of environmental and biological drivers on the survival of these young life stages. In this study, we use Generalised Linear Models to attempt to identify important local environmental (sea surface temperature and river flow) and biological (chlorophyll-a concentration and predator abundance) drivers of young sea bass abundance. We focus on seven British and Irish estuarine areas that are important to the northern stock of European sea bass. In four English estuarine areas there were good model fits to the abundance of young sea bass, but predictors differed amongst these suggesting that drivers of abundance may differ among individual nursery areas. This was further demonstrated by poor fits of models generated for English estuaries to interannual patterns of abundance in the Irish nursery areas tested. The differences found in the most important abundance drivers amongst areas highlight the complex and differing dynamics between estuaries. If the number of young bass that eventually join the adult stock is dependent on survivors from a diverse set of unique nursery area conditions, then endeavours to incorporate this knowledge into fisheries management should be further explored.

Large-scale electronic tagging is a very powerful tool to study how fish movements and migrations shape the internal dynamics of populations. This knowledge, crucial for improving fishery management, was still limited for the European seabass, whose stocks in the Northeast Atlantic have declined drastically over the last decade. To better understand the species ecology and the spatio-temporal structure of the population, we tagged seabass in the North Sea, the English Channel, and the Bay of Biscay, from 2014 to 2016. Out of 1220 deployed DSTs, 482 have been recovered by November 2022. Approximately half of them included a period of potential spawning migration. Reconstructed trajectories confirmed seabass to be a partial migratory species, as individuals exhibited either long-distance migrations or residence. Most migrants exhibited fidelity to summer feeding areas and winter spawning areas. Our dataset enriches the knowledge of seabass biological traits (e.g. temperature and depth ranges, vulnerability to predation and fishing). Our results suggest a spatial structure of the Atlantic population that differs from the stock structure currently considered for assessment and management. The consequences should be explored at both the European level and by regional managers involved in conservation outcomes. [ABSTRACT FROM AUTHOR]

IFN-I generates an antiviral state by inducing the expression of numerous genes, called IFN-stimulated genes, ISGs, including ISG15, which is the only ISG with cytokine-like activity. In a previous study, we developed the Dl_ISG15_E11 cell line, which consisted of E11 cells able to express and secrete sea bass ISG15. The current study is a step forward, analysing the effect of secreted sea bass ISG15 on RGNNV replication in E11 cells, and looking into its immunomodulatory activity in order to corroborate its cytokine-like activity. The medium from ISG15-produccing cells compromised RGNNV replication, as it has been demonstrated both, by reduction in the viral genome synthesis and, specially, in the yield of infective viral particles. The implication of sea bass ISG15 in this protection has been demonstrated by ISG15 removal, which decreased the percentage of surviving cells upon viral infection, and by incubation of RGNNV-infected cells with a recombinant sea bass ISG15 protein, which resulted in almost full protection. Furthermore, the immunomodulatory activity of extracellular sea bass ISG15 has been demonstrated, which reaffirms a cytokine-like role for this protein. • Extracellular sea bass ISG15 protects E11 cells from RGNNV infection. • Extracellular sea bass ISG15 reduces viral genome and infective viral particles in E11 cells. • Extracellular sea bass ISG15 modulates de transcription mx, tlr3 and hsp70 in E11 cells. [ABSTRACT FROM AUTHOR]

Abstract Several studies have attempted to understand the origin and evolution of single‐exon genes (SEGs) in eukaryotic organisms, including fishes, but few have examined the functional and evolutionary relationships between SEGs and multiple‐exon gene (MEG) paralogs, in particular the conservation of promoter regions. Given that SEGs originate via the reverse transcription of mRNA from a “parental” MEGs, such comparisons may enable identifying evolutionarily‐related SEG/MEG paralogs, which might fulfill equivalent physiological functions. Here, the relationship of SEG proportion with MEG count, gene density, intron count, and chromosome size was assessed for the genome of the European sea bass, Dicentrarchus labrax. Then, SEGs with an MEG parent were identified, and promoter sequences of SEG/MEG paralogs were compared, to identify highly conserved functional motifs. The results revealed a total count of 1,585 (8.3% of total genes) SEGs in the European sea bass genome, which was correlated with MEG count but not with gene density. The significant correlation of SEG content with the number of MEGs suggests that SEGs were continuously and independently generated over evolutionary time following species divergence through retrotranscription events, followed by tandem duplications. Functional annotation showed that the majority of SEGs are functional, as is evident from their expression in RNA‐seq data used to support homology‐based genome annotation. Differences in 5′UTR and 3′UTR lengths between SEG/MEG paralogs observed in this study may contribute to gene expression divergence between them and therefore lead to the emergence of new SEG functions. The comparison of nonsynonymous to synonymous changes (Ka/Ks) between SEG/MEG parents showed that 74 of them are under positive selection (Ka/Ks > 1; p = .0447). An additional fifteen SEGs with an MEG parent have a common promoter, which implies that they are under the influence of common regulatory networks.

Fish habitats sustain essential functions for fish to complete their life cycle, such as feeding, growing and spawning. Conservation is crucial to maintain fish populations and their exploitation. Since 2013, the spawning stock biomass of the northern stock of European seabass (Dicentrarchus labrax) has been in a worrying state. A series of low recruitments with a persistently high level of fishing has been blamed, raising concerns about the processes involved in seabass reproduction and settlement in nurseries. Here, we characterise seabass spawning areas along the French Atlantic coast using vessel monitoring system (VMS) data. A non‐linear geostatistical approach was applied, from 2008 to 2014, to detect locations where seabass aggregate for spawning. Occurrence maps of spawning distribution were combined into probability maps to quantify the seasonal and inter‐annual variability and to highlight recurrent, occasional and unfavourable spawning areas. We identified three main spawning areas: the Rochebonne Plateau in the Bay of Biscay, the Western English Channel and the North of the Cotentin peninsula in the Eastern English Channel. The correlative link between this geographical distribution and environmental factors was investigated using a Bayesian spatio‐temporal model. The spatio‐temporal structure accounted for the vast majority of the model predictive skills, whereas environmental covariates had a negligible effect. Our model revealed the persistence of the spatial distribution of spawning areas with intra‐ and inter‐annual variability. Offshore areas appear to be essential spawning areas for seabass, and should be considered in spatial management strategies. [ABSTRACT FROM AUTHOR]

Several studies have attempted to understand the origin and evolution of single‐exon genes (SEGs) in eukaryotic organisms, including fishes, but few have examined the functional and evolutionary relationships between SEGs and multiple‐exon gene (MEG) paralogs, in particular the conservation of promoter regions. Given that SEGs originate via the reverse transcription of mRNA from a "parental" MEGs, such comparisons may enable identifying evolutionarily‐related SEG/MEG paralogs, which might fulfill equivalent physiological functions. Here, the relationship of SEG proportion with MEG count, gene density, intron count, and chromosome size was assessed for the genome of the European sea bass, Dicentrarchus labrax. Then, SEGs with an MEG parent were identified, and promoter sequences of SEG/MEG paralogs were compared, to identify highly conserved functional motifs. The results revealed a total count of 1,585 (8.3% of total genes) SEGs in the European sea bass genome, which was correlated with MEG count but not with gene density. The significant correlation of SEG content with the number of MEGs suggests that SEGs were continuously and independently generated over evolutionary time following species divergence through retrotranscription events, followed by tandem duplications. Functional annotation showed that the majority of SEGs are functional, as is evident from their expression in RNA‐seq data used to support homology‐based genome annotation. Differences in 5′UTR and 3′UTR lengths between SEG/MEG paralogs observed in this study may contribute to gene expression divergence between them and therefore lead to the emergence of new SEG functions. The comparison of nonsynonymous to synonymous changes (Ka/Ks) between SEG/MEG parents showed that 74 of them are under positive selection (Ka/Ks > 1; p =.0447). An additional fifteen SEGs with an MEG parent have a common promoter, which implies that they are under the influence of common regulatory networks. [ABSTRACT FROM AUTHOR]

European sea bass is highly susceptible to the nervous necrosis virus, RGNNV genotype, whereas natural outbreaks caused by the SJNNV genotype have not been recorded. The onset and severity of an infectious disease depend on pathogen virulence factors and the host immune response. The importance of RGNNV capsid protein amino acids 247 and 270 as virulence factors has been previously demonstrated in European sea bass; however, sea bass immune response against nodaviruses with different levels of virulence has been poorly characterized. Knowing the differences between the immune response against both kinds of isolates may be key to get more insight into the host mechanisms responsible for NNV virulence. For this reason, this study analyses the transcription of immunogenes differentially expressed in European sea bass inoculated with nodaviruses with different virulence: a RGNNV virus obtained by reverse genetics (r Dl956), highly virulent to sea bass, and a mutated virus (Mut 247+270 Dl956, RGNNV virus displaying SJNNV-type amino acids at positions 247 and 270 of the capsid protein), presenting lower virulence. This study has been performed in brain and head kidney, and the main differences between the immunogene responses triggered by both viruses have been observed in brain. The immunogene response in this organ is stronger after inoculation with the most virulent virus, and the main differences involved genes related with IFN I system, inflammatory response, cell-mediated response, and apoptosis. The lower virulence of Mut 247+270 Dl956 to European sea bass can be associated with a delayed IFN I response, as well as an early and transitory inflammation and cell-mediated responses, suggesting that those can be pivotal elements in controlling the viral infection, and therefore, their functional activity could be analysed in future studies. In addition, this study supports the role of capsid amino acids at positions 247 and 270 as important determinants of RGNNV virulence to European sea bass. • IFN I system induction and NNV load in brain are positively correlated. • Low virulent NNV triggered an early inflammatory response in brain. • Low virulent NNV triggered a delayed IFN-I response. • Cathepsin is the main apoptotic gene involved in sea bass response after NNV infection. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the effect of replacing fish meal in the fish diet by zooplankton meal on the growth performance of European sea bass, Dicentrarchus labrax. A total of 900 fingerlings of the D. labrax were collected from fish hatchery Kilo 21, Alexandria and transported to the fish rearing unit in El-Max Research Station, National Institute of Oceanography and Fishers (NIOF), Alexandria, Egypt. After two weeks for acclimation, the fish were divided into 5 groups, 3 replicates for each group (60 fish in one cubic meter of Haba for each replicate). The five experimental diets were: G1: commercial diet (control group); G2, G3, G4, and G5 fish meal in this commercial diet was replaced by zooplankton meal as 25%, 50%, 75% and 100%, respectively. The highest values of growth performance parameters and PER & FER of D. labrax were recorded in G5, while the lowest values were recorded in the control group. The best average of FCR (1.75±0.02) was recorded for G5 and its bad average (2.18±0.18) was recorded in G1. The present study concluded that zooplankton positively affected growth performance parameters and enhanced feed utilization of sea bass. [ABSTRACT FROM AUTHOR]

Individual differences in diet can play an important role defining a population's ecological niche and its role within food webs and habitats, but individual trophic specialization is rarely considered in a fisheries context. Stocks of European seabass, Dicentrarchus labrax , have declined in recent years, and policy has focused on managing fishing effort. Inshore nursery grounds represent a critical habitat in terms of recruitment to standing stocks, and improved understanding of the ecology of juvenile seabass at the level of the individual may assist the development of management strategies aimed at maximizing their survival and growth. We quantified levels of individual trophic specialization in juvenile seabass using stomach contents and stable isotope analyses at a monthly resolution over an annual cycle. We found significant, seasonally varying levels of individual specialization in stomach contents, with reduced specialization observed in the spring. This was corroborated by stable isotope analyses, where isotopic variance among seabass individuals was significantly higher compared to that in two other concurrently sampled, sympatric bentho-pelagic predators. Our findings suggest that juvenile seabass form trophic-generalist populations composed of specialized individuals. Considering variation in individual behaviours may improve management strategies aimed at protecting the vulnerable life stages of this commercially important species. [ABSTRACT FROM AUTHOR]

From 2010 to 2012, 246 data storage tags were deployed on European seabass in the Iroise Natural Marine Park, a marine protected area (MPA) off west Brittany, France. A return rate of 14.6% associated with long time series of data provided new information on fish ecology (e.g. maximum experienced depth greater than 225 m, temperature range 6.80–21.87°C). Depth and temperature series were used to infer individual migration using an innovative hidden Markov model (HMM) especially developed for seabass geolocation. Reconstructed fish tracks revealed that seabass is a partially migratory species, as individuals exhibited either long-distance migrations towards the Bay of Biscay or the Celtic Sea, or residency behaviour in the Iroise Sea. Fidelity to summer feeding areas and to winter spawing areas was demonstrated. These results suggest that the population is spatially structured. The Iroise Sea is likely a mixing zone for different stocks or sub-populations, and may also shelter a resident population. At the population scale, such findings may impact ICES stock assessment and the resulting decisions from EU managers. At the local scale, conservation action could be taken by MPA managers. Besides, this study demonstrates the high potential of archival tags for investigating multi-year behavioural patterns such as site fidelity to offshore spawning areas. [ABSTRACT FROM AUTHOR]

Abstract The framework provided by the Dynamic Energy Budget (DEB) theory allows the quantification of metabolic processes and the associated biological rates that are of interest for aquaculture, such as growth and feeding. The DEB parameters were estimated for farmed European sea bass (Dicentrarchus labrax), a species of major importance for the Mediterranean aquaculture, using zero- and uni-variate literature data and achieving an overall good fit. The obtained parameter set was used to validate the model on sites representatively covering the geographic distribution of the aquaculture activity in Greece via comparison of model predictions to observations. Inter-individual variability of farmed fish was introduced through: 1) an individual initial weight and 2) a factor that acts as an individual-specific multiplier for some of the model parameters and produces scatter in maximum size, and age and size at puberty. Growth of E. sea bass was adequately predicted by the model while feeding tended to be underestimated, particularly during the period following the summer months when warmer temperatures promote high growth rates. The results suggest robustness of the model since it is able to simulate growth and food intake in several independent aquaculture production units, using a common parameter set. The accuracy of growth predictions supports the applicability of the model in variable environmental conditions in the context of climate change. Reconstruction of the feeding history from growth data revealed variations in the scaled functional response (f), i.e., the feeding rate as fraction of maximum possible one of an individual of a given size, throughout the production cycle. However, model simulations with constant f result in reasonably good predictions for growth and feeding in variable environmental conditions. Tendency of the model to underestimate the feeding process revealed both model weaknesses associated with higher temperatures as well as irregularities in the feeding protocols applied at the farm level. Our work demonstrates the capacity and potential of DEB theory for further development of tools that contribute to the assessment and improvement of feeding practices in aquaculture. Highlights • DEB parameter estimation for European sea bass and application to aquaculture • Model validation using production data from different aquaculture sites • Robustness of growth predictions allows simulation of climate change implications. • The model can provide insight towards improvement of food efficiency in aquaculture. [ABSTRACT FROM AUTHOR]

This report describes a study of the gonad differentiation in fingerlings of European sea bass (Dicentrarchus labrax) belonging to different size groups. Fishes were divided into four groups according to their weight: Group 1 (4.5 ± 0.7 g), Group 2 (9.2 ± 0.8 g), Group 3 (14.8 ± 1.8 g), and Group 4 (21.8 ± 2.3 g). In all groups, low percentages of undifferentiated or early sexually differentiated fish were found. Higher percentages of fully differentiated ovaries were found in Groups 1 and 3. Fully differentiated testes occurred in 90% of Group 4. Ninety percent of fish in Group 2 had gonads with intratesticular oocytes. This highlights the occurrence of intersexual cases and suggests that at this size, the fish is susceptible to phenotypic plasticity. The results of the present study show that sexual differentiation of the gonads is found in fish at 4.5 g weight. The ambiguous relationship between the observed gonad morpho-functional characteristics and fish size suggests a subject-dependent sexual differentiation. [ABSTRACT FROM AUTHOR]

Fish interferons are cytokines involved in its resistance to viral infections by inducing the transcription of several interferon-induced genes, such as isg15 . The aim of the present study was the genetic characterization of the European sea bass isg15 gene, describing the regulatory motifs found in its sequence. In addition, an in vivo analysis of transcription in response to betanodavirus (RGNNV genotype) and poly I:C has been performed. The analysis of the resulting sequences showed that sea bass isg15 gene is composed of two exons and a single 276-bp intron located at the 5′-UTR region. The full length cDNA is 1143-bp, including a 102-bp 5′-UTR region, a 474-bp ORF, and a 291-bp 3′-UTR region. Several mRNA-regulatory elements, including three unusual ATTTA instability motifs in the intron, and four ATTTA motifs along with a cytoplasmic polyadenylation element in the 3′-UTR region, have been found in this sequence. The in vivo analyses revealed a similar kinetics and level of transcription in fish brain and head kidney after poly I:C inoculation; however, the induction caused by RGNNV started earlier in brain, where the upregulation of isg15 gene transcription was high. The present study contributes to further characterize the European sea bass IFN I response against RGNNV infections. [ABSTRACT FROM AUTHOR]

Gamete activation in fish is an important step in terms of artificial fertilization of oocytes, cryopreservation studies and other experimental manipulations. Salinity and pH differences in activation media affect to sperm motility and fertilizing ability. These experiments were therefore designed to investigate the combined effects of pH (range 5.0–9.0) and salinity (20, 30, 37, and 45‰) of activation media on sperm motility of European sea bassDicentrarchus labrax. The best results were obtained at salinity 37‰ and a pH of 9.0. Our results also demonstrated that non-progressive motility at salinity 45‰ was observed in the range of 5.0–9.0 pH. In conclusion, spermatozoa can be motile at a wide range of pH and salinity values although the percent of motile spermatozoa and motility duration are negatively affected by low pH values. [ABSTRACT FROM PUBLISHER]

Muscular activity patterns in red and white muscles linked to oxygen consumption were studied during critical swimming tests in the sea bass (Dicentrarchus labraxLinnaeus 1758). The species is one of the most important for Mediterranean Sea aquaculture. A sigmoid model was used to fit both the oxygen consumption and red muscle activity while the white muscle activity pattern was described by an exponential model. Red muscle reaches an activation plateau close to critical swimming speed mostly due to the oxygen diffusion velocity in tissues. The exponential activation of white muscle appears to be linked to short and sudden periods of great energy need to cope with adverse conditions such as predation and escape. Both oxygen consumption and muscular activity were found to be size dependent. The bioenergetics of sea bass was modelled based on fish mass and swimming speed to predict the minimum and maximum speed as well as the mass-specific active metabolic rate and standard metabolic rate. An important finding was that contrary to other well-known species, swimming at subcritical speeds in sea bass involves both red and white muscle in different proportions. [ABSTRACT FROM PUBLISHER]

Dicentrarchus labrax were fed from 10 to 40 days posthatching with six microdiets differing in the inclusion level (60 g kg-1 and 120 g kg-1) and type of protein hydrolysate ( PH; yeast, YPH; pig blood, PBPH; pig red blood cells, PRBCPH). A microdiet containing 120 g kg-1 fish PH ( FPH) was used as a control. PH differed in their amino acid ( AA) profile and molecular weight distribution and therefore the tested microdiets too. The estimated content in FAA and di- and tripeptides in the FPH microdiet was 2 g kg-1 and 44 g kg-1, respectively. FAA estimated levels in YPH and PBPH microdiets were 26 g kg-1 and 53 g kg-1, whereas levels of di- and tripeptides were 30 g kg-1 and 60 g kg-1, respectively. The estimated levels of FAA in PRBCPH microdiets were 8 g kg-1 and 17 g kg-1, whereas estimated levels of di- and tripeptides were 11 g kg-1 and 22 g kg-1, respectively. Results revealed that FPH may be replaced by alternative PH from yeast and pig blood products, as fish fed those diets performed, in terms of growth, survival, digestive function and incidence of skeletal deformities, as well as those fed the FPH microdiet. Using YPH, PBPH and PRBCPH, the inclusion level of PH in microdiets might be reduced to a half with respect to current practices using FPH. [ABSTRACT FROM AUTHOR]

Sea bass is a major species in Mediterranean aquaculture, but has a distribution area ranging from North Atlantic to South Mediterranean, with a population structure previously revealed by population genetics. To test the farming performances of wild sea bass populations, we produced a partial diallel cross mating scheme, using sires originating from North Atlantic (NAT), South Atlantic (SAT), West Mediterranean (WEM), North-East Mediterranean (NEM) and South-East Mediterranean (SEM). Fifteen sires per origin were mated in a full-factorial design using artificial fertilization with 9 NAT dams and 17 WEM dams, producing 10 population crosses and 1950 potential full-sib families. All fish were reared together, then tagged at an average weight of 20g and distributed to four different sites (1800 fish per site). They were grown to an objective of 200g mean weight, where 737 to 775 fish were slaughtered in each site, and their parentage was recovered using 6 to 7 microsatellite loci, resulting in 98.9% unique assignments. All populations had similar growth rates until tagging size (20g), but differences appeared later on. No heterosis appeared for growth rate, and genotype by environment interaction (G×E) at the population level was limited, with a significant re-ranking only in one rearing site, while strong G×E for growth rate was observed within populations. Populations were different in shape, muscular fat content, and carcass yield, but not in fillet yield. In general, heterosis was absent and G×E was very limited between populations. No “ideal” population combining all favorable traits was identified. Differences between extreme populations ranged between 3 and 49% of the mean, depending on the traits. Interestingly, in almost all cases, these differences were within the reach of one generation of intense (5%) phenotypic selection. [ABSTRACT FROM AUTHOR]

Abstract: The European sea bass, Dicentrarchus labrax is a key species in fisheries and aquaculture in Europe and Africa. In fish farming, genetic tracking of broodstock and progenies, as well as artificial fertilization, is recommended in order to avoid genetic erosion in founder populations. Here we examined the performance of F1 fish from an artificially reproduced broodstock of European sea bass over a complete production cycle aimed at initiating a genetic program for growth improvement. Microsatellite multiplex data revealed that parental contributions were uneven in females but generally not in males. There were no indications of severe genetic bottlenecks over the entire production cycle and the artificial selection process. All data, along with an estimated h2 =0.49±0.15 for weight, confirm the suitability of the F1 adults to form a broodstock for initiating the genetic program. This study revealed two critical points that can seriously affect the success of seed production. First, at the larval stage, when families of progeny are mixed to start the production cycle, a balanced parental contribution should be attained. Second, the distribution of the F1-selected breeders into spawning batches should be designed using coancestry data, in order to maintain optimal levels of genetic variability in the next generation. Both procedures practiced over successive generations should help to sustain the genetic health of European sea bass stocks over many production cycles. [Copyright &y& Elsevier]

The present study examined the influence of early-rearing temperature—which favors the development of male-dominant or female-dominant populations—in European sea bass Dicentrarchus labrax on haemal lordosis and growth performance until harvest time (mean body weight>400g). European sea bass were reared at 15 or 20°C from egg to metamorphosis (~17mm in total length), which lasted for 66 and 55days post spawning (dps), or 990 and 1100°C-days, respectively. Thereafter, rearing until harvest time (715dps) followed a common temperature regime, ranging between 14.5°C in February and 26.5°C in August. As expected from previous studies, the effect of early-life rearing temperature was significant on mean (±SEM) sex ratio (78±2% females at 15°C vs. 29±2% females at 20°C) and there was a highly significant (P<0.01) growth advantage in favor of the 20°C fish at the end of the first year. However, there was no significant difference in body weight between the two temperature groups by harvest time, indicating the expression of compensatory growth in the 15°C group. The mean occurrence of haemal lordosis incidence was evaluated using X-rays at the end of the nursery phase (145dps) and was shown to be significantly higher in the 20°C group (90±0.4%) compared to the 15°C group (41±0.8%). The occurrence of haemal lordosis upon external image evaluation at harvest time decreased to 0% in the 15°C group compared to 36±7% in the 20°C group. Almost half of these latter fish with haemal lordosis were considered unmarketable due to heavy deformation. These findings demonstrated that rearing European sea bass at low temperatures during early life can result in significant gains for aquaculture industry, through increases in female proportion—and therefore growth performance—and reductions in skeletal abnormalities. The study also demonstrated that even fish with heavy haemal lordosis could grow as well as normal fish, thus competing for food with normal fish and resulting in financial loss for the industry due to their unmarketability. [ABSTRACT FROM AUTHOR]

Abstract: Mx proteins are key components of the antiviral state triggered by interferon type I in response to viral infections. In this study, two different Mx genes have been identified in European sea bass (Dicentrarchus labrax), and their sequences were cloned and characterized. MxA cDNA consists of 1881bp coding for a putative 626 aminoacids protein, while MxB cDNA has 1920bp and results in a protein with 639 residues. Their corresponding genomic sequences contain 3538bp and 5326bp, respectively, and both present 12 exons and 11 introns. The expression patterns of the two Mx genes after an in vivo challenge with the viral nervous necrosis virus (VNNV), a serious pathogen in farmed European sea bass, have been characterized by real-time PCR. The results showed interesting differences in the transcription profile of both Mx, thus suggesting a differential role for each Mx isoform in the immune response of European sea bass to VNNV, and most likely in the general viral response of this species. [Copyright &y& Elsevier]

Skeletal deformities are important traits for aquaculture as they induce slow growing and low market value. We studied their genetic determinism and their interactions with the environment at the ongrowing stage in 5839 European sea bass from a partial factorial mating of 33 sires and 23 dams, reared in four sites. All families were mixed, and fish were first reared in one site (site B) until 35 g mean weight, then distributed to the four sites. A posteriori reconstruction of pedigree with microsatellites was used. Deformities were scored internally at slaughtering, and externally from photographs. Site B, where all fish were initially stocked until 35 g and exposed to forced swimming because of fast water current showed the highest rate of deformities with 83% and 65% from internal and external scoring respectively. Heritability on the underlying scale was h2 = 0.25 ± 0.03 across all sites, and varied little between sites, while genetic correlations of deformities between sites were always high (>0.85). Genetic correlations between deformities and daily growth coefficient were variable between sites( rA = 0.50 ± 0.09, 0.43 ± 0.10, 0.32 ± 0.10, 0.18 ± 0.10 for sites A, B, C, D respectively) and were positively linked with the average growth rate in each site. These results pointed out that there could be a relation between growth rate and the evolution of deformities at the grow-out stage. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effect of freshwater rearing on the fatty acid profiles of the whole body and muscle tissue of the European sea bass ( Dicentrarchus labrax). Half of initial fish were gradually acclimated to freshwater (FW) kept at the same temperature to salt water and grown in same conditions as their counterparts in saltwater (SW). The decrease in salinity caused an increase in the percentages of 18:1 n − 9, 24:1 n − 9, 18:3 n − 3, 18:2 n − 6 and decrease in the percentages of 14:0, 15:0, 20:0, 21:0, 20:5 n − 3 and 22:6 n − 3 both in the whole body and in the muscle tissue fatty acid profiles. The lipids of FW-reared fish contained significantly ( P < 0.01) higher percentages of 18:2 n − 6 and 18:3 n − 6 than that of SW-reared fish. However, percentages of 20:5 n − 3 and 22:6 n − 3 fatty acids decreased significantly ( P < 0.05) compared with those of salt water-reared European sea bass. There was a clear trend of decrement in the percentages of n − 3 PUFA fatty acids due to the decrease in water salinity. However, the percentages of n − 6 PUFA fatty acids were also increased with the decrease in water salinity. We concluded that the FW acclimation is followed by changes in certain lipid classes of sea bass muscle tissue and whole body samples. n − 3/ n − 6 PUFA ratios were characteristic to previously reported ratios for both FW- and SW-reared European sea bass. In addition, EPA/DHA ratios were basically similar for the fish reared in both SW and FW indicating the equal nutritional value of the final products in terms of providing PUFA's for human nutrition. [ABSTRACT FROM AUTHOR]

Natural mating and mass spawning in the European sea bass ( Dicentrarchus labrax L., Moronidae, Teleostei) complicate genetic studies and the implementation of selective breeding schemes. We utilized a two-step experimental design for detecting QTL in mass-spawning species: 2122 offspring from natural mating between 57 parents (22 males, 34 females and one missing) phenotyped for body weight, eight morphometric traits and cortisol levels, had been previously assigned to parents based on genotypes of 31 DNA microsatellite markers. Five large full-sib families (five sires and two dams) were selected from the offspring (570 animals), which were genotyped with 67 additional markers. A new genetic map was compiled, specific to our population, but based on the previously published map. QTL mapping was performed with two methods: half-sib regression analysis (paternal and maternal) and variance component analysis accounting for all family relationships. Two significant QTL were found for body weight on linkage group 4 and 6, six significant QTL for morphometric traits on linkage groups 1B, 4, 6, 7, 15 and 23 and three suggestive QTL for stress response on linkage groups 3, 14 and 23. The QTL explained between 8% and 38% of phenotypic variance. The results are the first step towards identifying genes involved in economically important traits like body weight and stress response in European sea bass. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a survey of sea bass, Dicentrarchus labrax, for amoebae and scuticociliatidia infections was carried out to evaluate their effects on the aquaculture of this fish species. The study was conducted in two different fish farms, one using seawater and the other brackish water. Infection with parasitic amoebae was found to be fairly high (prevalence: 43–73%), being more frequent in sea bass from the brackish water system. Although it was never found to cause outbreaks of disease or mortality in the surveyed fish, amoebic gill disease (AGD) histopathological signs, i.e., hyperplasia, secondary lamellae fusion and cavity formation (interlamellar vesicles), were observed in fish manifesting no macroscopic lesions. Furthermore, some evidence was found that amoebae affects the fish''s general state of health and growth rate. These results indicate that cautious and detailed surveys to detect this sort of infection, and thus carefully plan its control, are fully justified. Compared with amoebic infection, the prevalence of scuticociliatosis was found to be low (7–13%). No outbreaks of disease or mortality were ever recorded, even when scuticociliatidia was present in turbot raised in the same water system, leading to serious outbreaks of disease and mortalities in that species. This suggests that sea bass is far more resistant than turbot to such infections, and if this is the case, the former fish may be a good farming alternative when scuticociliatidia is present. [Copyright &y& Elsevier]

A method of geometric morphometrics was used to characterize body shape variation in meiotic gynogenetic and triploid sea bass in comparison with diploid controls. A total of 13 coordinate landmark data were recorded on the profile of 34-month-old control (n = 81), gynogenetic (n = 117) and triploid (n = 131) siblings generated from two females (A and B). Three main axes of morphometric variation were consistent, and these accounted for 60.8 and 57.6% of the total variability in females A and B, respectively. There were significant shape deviations of triploid and gynogenetic fish relative to the controls, and differences were particularly evident in the progeny of one female. Overall, triploids displayed a more slender shape than diploids, whereas gynogenetic fish were deeper bodied and had flexed caudal peduncles and cranial features. The results are discussed especially in relation to the characterization of triploid fish for commercial purposes. [ABSTRACT FROM PUBLISHER]

Abstract: Selective breeding to improve residual feed intake (RFI) in sea bass (Dicentrarchus labrax) is a major goal that would optimize economic gain while minimizing the environmental impact of production. Due to the difficulty in accurately measuring individual feed intake, no selective breeding program has yet been started. In a previous study, we identified a criterion phenotypically related to RFI variations: the loss of weight during feed deprivation, FD. Moreover, an additional composite criterion (CC) integrating both FD and weight gain during subsequent re-feeding (RF) was closely related to RFI, even though the relationship was only close to significance (P =0.06). The aim of the present study was to estimate the heritability of these two traits, in order to complete the analysis of their pertinence as indirect criteria for use in a selective breeding program to improve RFI. We set up a full factorial mating design combining 41 sires and eight dams to produce mixed families offspring, which were all raised in the same tank. At 50g, 1300 individuals were individually tagged and a fin clip was sampled for DNA extraction and parentage reassignment using five to six microsatellite loci, which showed they originated from 261 families. The evolution of individual body weight was recorded during a growth period of three weeks, followed by successive periods of three weeks feed deprivation and three weeks ad libitum re-feeding, repeated twice. Phenotypic and genetic correlations between the two feed deprivation periods or the two re-feeding periods were moderate (r =0.45–0.51, and 0.71–0.73 respectively for phenotypic and genetic correlations) indicating that FD and RF are relatively repeatable. FD, RF and CC heritabilities were of the same magnitude (0.23±0.04, 0.19±0.04 and 0.22±0.04, respectively), and sufficient to consider the use of such criteria in a future breeding program. [Copyright &y& Elsevier]

The article discusses a study which investigated the isolation of Shewanella putrefaciens from cultured European sea bass in Turkey. According to the author, the sick fish showed lethargy, loss of appetite, exophthalmus, and ulcers on the dorsal part of the body, and liver haemorrhages as well as spleen enlargement were observed. The gram-negative, cytochrome oxidase and catalase positive and hydrogen sulfide (H2S) producing rods, which was identified as Shewanella putrefaciens, were isolated from skin ulcers, kidney, spleen, liver, and blood. It notes that sea bass infected with Shewanella putrefaciens shows depletion of white and red pulpas.

Abstract: Malformations in farmed fish are a prime research topic as it has a major impact on fish welfare and on the economical value of the product. In this study, the genetic component of spine deformities was estimated in European sea bass, a major species of Mediterranean aquaculture, with the use of a posteriori reconstruction of pedigree with microsatellites. Our population exhibited a very high malformation rate (81%), probably due to intense swimming of fish during pre-growing. The heritability of global spine deformities was evaluated to be 0.21±0.04 on the underlying scale (0.33±0.06 for lordosis, 0.13±0.04 for scoliosis). Deformities scored by an internal or external examination turned out to be genetically the same trait (genetic correlations>0.9), although phenotypic correlations were moderate to high (0.45±0.04 to 0.92±0.01) due to difficulties in scoring the less severe deformities. Along time (from 100 to 800g mean weight), lordosis had a constant heritability, with very high genetic correlations between stages (>0.9). Its incidence increased from 39 to 53% indicating that the malformation was probably present from the beginning of the rearing period but that its expression increased over time. A positive linkage between spine deformities and growth rate was demonstrated both by the higher early weight of affected fish and by the positive genetic correlation between weight and malformation (from 0.21±0.15 to 0.40±0.14), although deformities have a negative phenotypic impact on growth. However, heritabilities of malformation traits calculated here are only estimates that may indirectly describe the sensitivity of fish to the particular pre-growing environment as a function of different body weight genotypes. A quantification of realised heritability would therefore be necessary before concluding on the existence of a genetic basis for spinal malformations such as lordosis and scoliosis. Nevertheless and by precaution, selection for fast growth rate needs careful monitoring of deformities, and selection against malformations may counteract impacts of selection for fast growth. [Copyright &y& Elsevier]

Abstract: Selective breeding of European sea bass (Dicentrarchus labrax) receives a growing interest, as the estimated heritability of growth is medium to high. In this study, we compared the offspring of four groups of sea bass sires, mated with the same wild dams: wild (W), first generation of domestication (D), first generation of mass selection for length (M), first generation of PROSPER-like selection for length (P). The comparison was done both in replicated tanks (separate rearing) and in mixed tanks (mixed rearing) where sire origins were recovered by genotyping of eight microsatellite markers. Weight, length and growth rate were measured from day 238 post-fertilization (69 g mean weight) to day 611 post-fertilization (390 g mean weight). Both in mixed and separate tanks, both selected groups (P, M) were larger than unselected groups (W, D). No difference was seen at any time between W and D, nor between M and P. The selection response estimate on weight was larger in mixed tanks when compared to separate tanks (+42% in mixed tanks, +23% in separate tanks at day 611), yielding realized heritability estimates of 0.60 and 0.34, respectively, and confirming the excellent potential of the species for growth improvement through selective breeding. Both selection response and the amplification effect between mixed and separate tanks decreased as rearing density increased. Our hypothesis is that selection response is magnified by competition in mixed tanks, while sub-optimal rearing conditions lower the observed selection response, more in separate tanks (where selected thus larger fish are at a higher density than unselected ones) than in mixed tanks (where all fish experience the same density effects). [Copyright &y& Elsevier]

Total lipid amount and fatty acid composition were determined and compared for cultivated European sea bass (Dicentrarchus labrax) from Turkey, which were fed with pellet and extruded commercial feed two or three times a day. Fatty acid analyses were carried out by gas chromatography-mass spectrometry. Among total fatty acids, palmitic (16:0), palmitoleic (16:1 n-7), oleic (18:1 n-9), linoleic (18:2n-6), eicosapentaenoic acid = EPA (20:5n-3) and docosahexaenoic acid = DHA (22:6n-3) were found to be the predominant fatty acids. The fish which received extruded feed (three times a day) had a slightly higher n- 3/n-6 ratio of 1.41 compared to the other feeding types. It was found that the extruded feed given two times a day as fish diet resulted in the highest amounts of EPA, DHA, and total n-3 fatty acids. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we investigate the interleukin-10 (IL-10) expression and 3D modelling of the European sea bass (Dicentrarchus labrax L.). IL-10 is a regulatory cytokine that has been intensively studied in mammals and has been found mainly involved in the suppression or deactivation of activated immune responses. The full-length sea bass IL-10 cDNA consists of 1015 bp and is translated in a predicted molecule of 187 amino acids. A multiple alignment of this peptide with other known sequences showed the conservation of fundamental IL-10 family characteristics. Expression analysis by real-time PCR in control fish showed a high basal expression in the head kidney (HK), followed by gut and brain. In vitro treatment of HK leucocytes with LPS showed an intense increase of IL-10 expression at 4 h and a significant decrease at 24 h, with PHA-L no differences were evidenced. A 3D model for sea bass IL-10 was obtained by accurate homology procedures and putative interaction residues with the IL-10 receptor described. The results suggested that sea bass IL-10 could be involved in anti-inflammatory responses, but further experiments are needed to assess its importance in response to pathogenic agents, vaccinations and immunostimulants. [Copyright &y& Elsevier]

1. Stable isotope data are widely used to track the origins and transformations of materials in food webs. Reliable interpretation of these data requires knowledge of the factors influencing isotopic fractionation between diet and consumer. For practical reasons, isotopic fractionation is often assumed to be constant but, in reality, a range of factors may affect fractionation. 2. To investigate effects of temperature and feeding rate on fractionation of carbon and nitrogen stable isotopes in a marine predator, we reared European sea bass Dicentrarchus labrax on identical diets at 11 and 16 °C on three ration levels for 600 days. 3. Nitrogen trophic fractionation (Δδ15N) was affected by temperature. Bass Δδ15N was 4·41‰ at 11 °C and 3·78‰ at 16 °C. 4. Carbon fractionation (Δδ13C) was also affected by temperature. Bass Δδ13C was 1·18‰ at 11 °C and 1·64‰ at 16 °C. The higher lipid content in the tissues of bass reared at cooler temperatures accounted for the temperature effect on Δδ13C. When Δδ13C was determined using mathematically defatted values, there was a direct effect of ration size and Δδ13C was 2·51, 2·39 and 2·31‰ for high, medium and low rations, respectively. 5. Reported Δδ15N for all treatments exceeded the mean of 3·4‰ widely used in ecological studies of fish populations and communities. This would confound the interpretation of δ15N as an indicator of trophic level when comparing populations that are exposed to different temperatures. 6. The Δδ13C of 0–1‰ commonly applied in food web studies did not hold under any of the temperature or feeding regimes considered and a value of 2‰ would be more appropriate. [ABSTRACT FROM AUTHOR]

In order to study the effects of bath vaccination against vibriosis in European sea bass fingerlings, Dicentrarchus labrax L. 1758, reared in Sardinia in land-based concrete tanks and sea cages, a commercial preparation was used. The achievement of the immune response, the presence of the disease and the growth performances were determined monthly in a one year study. The results showed an increase of antibody titers in immunized fish when compared to the controls. Moreover, although vibriosis spreads every year in the farms, and also during the trials year, no disease outbreaks were observed in the immunized fish. Regarding growth performances, a significant difference on body weight's increase was recorded only in off-shore cultured immunized fish when compared to the controls. Furthermore, a better “general condition” of immunized fish was recorded; therefore a higher production, at least 10%, was estimated. [ABSTRACT FROM PUBLISHER]

Abstract: The effects of abrupt transfer to lower salinity (8, 18, 28‰ and ambient) of European sea bass, Dicentrarchus labrax, and gilthead sea bream, Sparus aurata, juveniles on their behaviour, daily rates of growth and feeding, maintenance requirement and food conversion efficiency were studied. Both species showed similar behaviour during the acclimation period regardless the salinity. During the first day, the fish show sharp reactions to the feeding stimuli and the presence of the researcher who provides the food. In the next 2–3 days the fish show smoother reactions and from the 7th day and on compete for food. Daily growth rates of sea bass were found higher at salinities above 28‰ while for gilthead sea bream were found higher between 18‰ and 28‰. Maximum growth rates were found higher for gilthead sea bream than sea bass at each salinity. Maintenance requirement was found to increase with decreasing salinity. European sea bass showed higher maintenance requirements than the gilthead sea bream. The highest values of food conversion efficiency were obtained for salinities above 28‰ for sea bass and between 18 and 28‰ for gilthead sea bream. The optimum salinity conditions for sea bass are above 30‰ while for gilthead sea bream, are between 18‰ and 20‰. [Copyright &y& Elsevier]

In an 83-day-nutrition trial, effects of feed production technique and feeding frequency on feed intake, growth and nutrient utilization were determined in European sea bass (Dicentrarchus labrax). Three thousand six hundred fish (170 ± 2.6 g) were randomly allocated to experimental sea cages (approx. 5800 l) according to a 2 x 2 experimental plan [2 processing techniques: steam pelleted diet (P) vs. extruded diet (E); 2 feeding frequencies: twice (2) vs. 3 times (3)]. The P3 group consumed significantly (P < 0.05) more feed than the fish fed extruded diets, irrespective of feeding frequency. Growth rates of all groups did not display any significant difference (P > 0.05) in terms of final weight (FW) or specific growth rate (SGR), although there was a decreasing trend in final weight (E3 > E2 > P3 > P2). Feed efficiencies (FE) of E2 and E3 fish were higher than P2 and P3 treatments (P < 0.05). No significant difference (P > 0.05) was evident for the hepatosomatic index (%), mesenteric fat index (%), viscerasomatic index (%), or dress-out (%) parameters in all treatments. The carcass and muscle components (protein, lipid, and ash) did not reveal any significant difference (P > 0.05). According to the results, feeding sea bass twice or 3 times daily with steam pelleted or extruded diet did not influence the growth; however, extruded diet improved the feed efficiency of sea bass irrespective of feeding frequency. [ABSTRACT FROM AUTHOR]

Abstract: The aims of the present study were (a) to compare sperm quality (percentage of motile spermatozoa, motility duration, density and fertility after cryopreservation) between precocious and normally maturing male European sea bass Dicentrarchus labrax, (b) to examine the potential of human chorionic gonadotropin (hCG) to increase spermiation in precocious males and (c) to examine the potential of hCG to induce spermatogenesis and spermiation in non-precocious 1-year-old males. One hundred precocious and 100 non-precocious fish were each randomly divided in two groups each: control (precocious saline-treated and non precocious saline-treated) and treated (precocious hCG-treated and non precocious hCG-treated). Treated groups were administered weekly with 1000 IU hCG kg−1 body weight while control groups were injected with physiological solution. Milt volume produced, sperm concentration, motility duration and fertilising ability were assessed every week in each group. The effect of the hormonal treatment on gonadal development was examined based on the gonadosomatic index and testicular histology. The results demonstrate that sperm produced by precocious fish has characteristics (mean value of motility class, mean maximum motility duration, concentration and fertility after cryopreservation) similar (P >0.05) to those produced by 2-year-old fish. Human chorionic gonadotropin treatment in precocious fish resulted in a significant increase (P <0.05) of milt volume, without affecting sperm quality. In non-precocious fish, hCG treatment resulted in greater percentage of spermiation (P <0.05) compared to non-precocious saline-treated group. At the end of the trial (three weeks), 29 out of 50 non-precocious hCG-treated fish were spermiating and, within these 23 produced >200 μl per fish of milt. No differences were observed in terms of sperm concentration, motility class, motility duration and fertilizing capacity due to hCG treatment in either precocious, or non-precocious fish. In addition, analysis of the testicular histology of fish that did not spermiate after hCG treatment, shows a significant (P <0.05) enhancement of testicular development stages. The present study demonstrated that (a) precocious European sea bass males produce milt of comparable sperm characteristics to adult individuals, (b) treatment of non-precocious males with hCG induced spermatogenesis and spermiation and (c) treatment of precocious males with hCG enhanced milt volume without affecting other sperm characteristics, including fertilizing ability. [Copyright &y& Elsevier]

Abstract: In this paper we describe the cloning, expression and structural study by modelling techniques of the CD8α from sea bass (Dicentrarchus labrax L.). The sea bass CD8α cDNA is comprised of 1490bp and is translated in one reading frame to give a protein of 217 amino acids, with a predicted 26 amino acids signal peptide, a 88bp 5′-UTR and a 748bp 3′-UTR. A multiple alignment of CD8α from sea bass with other known CD8α sequences shows the conservation of most amino acid residues involved in the peculiar structural domains found within CD8α''s. Cysteine residues that are involved in disulfide bonding to form the V domain are conserved. In contrast, an extra cysteine residue found in most mammals in this region is not present in sea bass. The transmembrane and cytoplasmic regions are the most conserved regions within the molecule in the alignment analysis. However, the motif (CXCP) that is thought to be responsible for binding p56lck is missing in the sea bass sequence. Phylogenetic analysis conducted using amino acid sequences showed that sea bass CD8α grouped with other known teleost sequences and that three different clusters were formed by the mammalian, avian and fish CD8α sequences. The thymus was the tissue with the highest CD8α expression, followed by gut, gills, peripheral blood leukocytes and spleen. Lower CD8α mRNA levels were found in head kidney, liver and brain. It was possible to create a partial 3D model using the human and mouse structures as template. The CD8α 11–120 amino acid region was taken into consideration and the best obtained 3D model shows the presence of ten β-strands, involving about 50% of the sequence. The global structure was defined as an immunoglobulin-like β-sandwich made of two anti-parallel sheets. Two cysteines were present in this region and they were at a suitable distance to form an S seen in the template human and mouse structures. [Copyright &y& Elsevier]

Continuous cell lines represent an important tool both for biological studies and for their applications in marine biotechnology. In this article we describe the production and characterization of a continuous adherent cell line, named DLEC, derived from early embryos of the European sea bass Dicentrarchus labrax L. (Actinopterygii, Moronidae). Cells were obtained by disrupting 2- to 12-hour-old embryos and culturing resulting cells at 18°C in RPMI medium containing 5% fetal calf serum (FCS) and 10% supernatant fraction of the embryo homogenate. After 8 weeks culture medium was replaced with Liebovitz's L15 medium containing 10% FCS and DLEC cells started proliferation. Subsequently, they were continuously cultured until the 50th passage without evident changes in their morphology. DLEC cells show a fibroblast-like shape and a modal chromosome number of 48, as do the wild-type cells; conversely the constant presence of six to nine meta-submetacentric elements in the karyotype (vs. zero to two in the wild-type) indicates the occurrence of chromosomal rearrangements during stabilization. DLEC cells are sensitive to substances known to induce differentiation of mammalian cells such as retinoic acid and phorbol esters. They have been transfected using liposomes with a commercial plasmid vector containing a reporter gene, thus suggesting a possible importance as an alternative expression system of recombinant vertebrate proteins in teleost cells. [ABSTRACT FROM AUTHOR]

Abstract: Reproduction by mitotic gynogenesis was carried out in European sea bass, Dicentrarchus labrax L., by fertilizing eggs from three normal and one meiotic gynogenetic females with UV-irradiated sperm. The haploid chromosome set was then doubled by applying a pressure shock at 81 or 91 MPa for 4 min at the time of the onset of the first cleavage furrow in order to obtain four progenies of mitotic gynogenetic double haploid (G2N) fish. Haploids, tetraploids and normal diploids were also produced as controls. Survival of G2N prelarvae was 7–18% of that of normal diploids. The diploid status of G2Ns was verified by flow cytometry, while maternal chromosome inheritance was confirmed by unilocus analysis of six microsatellites amplified by hexaplex PCR and by the precocious death of haploid controls. Two progenies were found to be completely homozygous for the heterozygous maternal microsatellite alleles while, in the other two progenies, only 92% and 95% of the fish were fully homozygous, as 7 fishes were heterozygous at one locus, 6 at two, and 1 at three loci. Similar small percentages of triploid fish were found within the corresponding tetraploid controls. No increment of heterozygous or triploid fish was observed in successive samplings. In the most numerous progeny, 100 fish have been raised for 2 years and some of them are essentially of normal appearance. In these G2Ns, 16 double haplotypes were found on the basis of the 6 microsatellite loci analyzed. The possible use of G2Ns as clonal founders for sex control and performance improvement is discussed. [Copyright &y& Elsevier]

Three practical isoproteic (54% protein) diets were formulated to contain graded levels of crude fat (diet L: 10%, diet M: 20% and diet H: 30%). Each diet was assigned unrestrictedly to three and restrictedly to two replicate groups of fish (IBW 243 g). In unrestricted groups, increasing the dietary lipid level led to a significant decrease in voluntary feed intake without affecting growth rate. In the feed-restricted groups, daily growth rates increased with increasing dietary fat levels. There was a significant and inverse effect of the dietary fat content on whole body moisture and fat levels, with highest lipid (ca. 20%) and lowest moisture (ca. 58%) contents in sea bass fed diet containing the highest lipid level; muscle lipid concentration was however not affected. Nitrogen retention was significantly increased by an increase in lipid concentration in the diets, with better efficiencies observed in unrestricted (ca. 31%) than in restricted groups (ca. 27%). Nitrogen loss was significantly affected by both the feeding level and the diet composition, with lowest values (ca. 60 g kg−1) in groups fed diet H unrestrictedly and highest values (ca. 90 g kg−1) in groups fed diet L at a restricted level. Soluble phosphorus excretion in H groups was less than half that in L groups, regardless of the feeding level. [Copyright &y& Elsevier]

Two experiments were conducted in triplicate in order to study the effect of stocking densities on survival (highlighting sibling cannibalism), growth and feeding of intensively cultured sea bass larvae (50, 100, 150 and 200 fish l−1) and post-larvae (5, 10, 15 and 20 fish l−1). Experimental populations were reared under controlled conditions in 50-l cylindroconical tanks. Dead fish were counted daily and classified into cannibalised and non-cannibalised. Total length and weight were measured weekly. Results indicate that stocking density did not affect survival and growth of larvae. No cannibalistic phenomena were observed at this stage. On the other hand, survival of post-larvae was higher at 5 and 10 fish l−1 than at 15 and 20 fish l−1, while growth performance fluctuated between the lowest value recorded in the group of 10 fish l−1 and the highest value in that of 5 fish l−1. Feed intake in post-larvae was independent of stocking density. Cannibalism was the main cause of death in post-larvae. Two types of cannibalism were detected: type I, attack from tail (observed at the beginning of this stage) and type II, attack from head (observed at the end of the stage). [Copyright &y& Elsevier]

Cytochrome P450arom, a key enzyme in the hormonal steroidogenic pathway, mediates the conversion of androgens to estrogens. This work describes the molecular cloning of the cDNA encoding the European sea bass (Dicentrarchus labrax L.) cytochrome P450arom by means of reverse transcriptase and polymerase chain reaction (RT–PCR) and 5′ and 3′-rapid amplification of cDNA ends (RACE) analyses. The cDNA is 1822 bp in length and encodes a putative protein of 517 amino acids. Northern blot analysis revealed that the ovary expressed a transcript of about 2.2 kb in size. Analysis of the deduced amino acid sequence indicated 62–86% identity with ovarian P450arom of other teleost fish, the highest identity being found with the Japanese flounder, Paralichthys olivaceous. Identity was lower (56–65%) with the P450arom forms first reported in teleost brain. Only 52% identity was observed with the corresponding fragment of the cartilaginous fish, Dasyatis sabina. RT–PCR revealed that the sea bass P450arom mRNA was also expressed, at low levels, in testis and brain. Between the 5′ and 3′-untranslated terminal regions (UTR), the sea bass CYP19 gene contains eight introns. All introns conform to the GT/AG rule for RNA splicing and are inserted in exactly the same positions as those found in Oryzias latipes and the human CYP19 gene. [Copyright &y& Elsevier]

Two 40-day feeding trials using extruded diets were conducted to assess the effect of a dietary phospholipid (PL) supplementation on growth, survival and fatty acid composition of European sea bass (Dicentrarchus labrax) and turbot (Scophthalmus maximus) from weaning onwards. Two dietary treatments (FO and PL) were tested; both had an identical extruded basis (92.5% total diet weight) coated with a different lipid fraction (7.5% total diet weight). Diet PL contained 2% egg yolk PL (69% pure). In diet FO the PL was replaced by hydrogenated coconut oil. The isolipidic diets contained an equal amount of fish oil ethyl esters providing 1.6% (% diet dry weight) of n-3 highly unsaturated fatty acids (HUFA). A diet water stability test showed no effect of the PL supplementation on the leaching of the dietary fatty acids. In both fish species weight, but not survival, significantly increased as a result of PL supplementation. Weaning onto the experimental diets resulted in similar changes in the relative percent levels of fatty acids in both species. In general, the percentage of saturated fatty acids levelled off after a rapid increase, while monoenes increased after an initial decrease. Total n-3 polyunsaturated fatty acids (PUFA) decreased and total n-6 PUFA remained almost constant. The major effect of the dietary PL on fish fatty acid composition was a 50% increase in n-6 and n-3 HUFAs compared to the PL-free FO diet. The rise in n-6 HUFA may have reflected the higher moiety in the dietary PL. On the other hand this was not the case for the n-3 HUFA since they represented only low levels in the PL fraction (0.1%) compared to that provided by the ethyl esters (1.6%) suggesting a more efficient incorporation of the PL n-3 HUFA than of the ethyl ester n-3 HUFA. A second hypothesis is that the dietary PL may have favored the incorporation of the dietary ethyl ester n-3 HUFA. [ABSTRACT FROM AUTHOR]