European seabass

The long term effects of moderate elevation ORP (oxidation-reduction potential) around 300-320 mV on the growth, hematological parameters and the ability of European seabass (Dicentrarchus labrax) to react against bacterial infection was studied in recirculating aquaculture systems (RASs). Two RASs, one with a moderate ozonation (RAS-O-3) and a control (RAS-C) were used in this experiment. After 60 days, seabass reared in the RAS-O-3 were more able to react against a Vibrio anguillarum infection. It was in spite of the fact that seabass in the RAS-O-3 showed decreased feed intake, feed conversion rate, growth rate and modified hematological parameters compared with the fish in RAS-C. It is obvious that an ORP level of 300-320 mV is too high for seabass to adapt in terms of the growth performance and the hematological parameters. However the increased ORP resulted in a better ability of the fish to react against bacterial infection. Our results strongly suggest that ORP for seabass i...

The relationships among 15 morphometric measurements in 219 aliquots of European seabass (Dicentrarchus labrax) were examined with respect to sexual dimorphism. The ratio of females to males was determined as 1:5.1 and gonadosomatic indices (%) were found for males (2.13 ± 0.86) and females (3.63 ± 1.18). There were 4 morphometric characteristics that differed between genders: ventral margin of cleithrum (VMC), postanal fin length (post-AFL), postdorsal fin length (post-DFL), and preanal fin length (pre-AFL). Although there were significant differences between morphometric characteristics (post-AFL, post-DFL, pre-AFL) and total length, no significant differences were found in the VMC. These average ratios were determined as pre-AFL to TL 0.61 ♀, 0.71 ♂; post-AFL to TL 0.72 ♀, 0.84 ♂; post-DFL to TL 0.68 ♀, 0.81 ♂, respectively. The aim of this study was to investigate if sexual differences could affect external morphology in cultured seabass and, additionally, to determine sexual dimorphism related to morphological differences during the maturation and spawning seasons in this species.

The relationships among 15 morphometric measurements in 219 aliquots of European seabass (Dicentrarchus labrax) were examined with respect to sexual dimorphism. The ratio of females to males was determined as 1:5.1 and gonadosomatic indices (%) were found for males (2.13 ± 0.86) and females (3.63 ± 1.18). There were 4 morphometric characteristics that differed between genders: ventral margin of cleithrum (VMC), postanal fin length (post-AFL), postdorsal fin length (post-DFL), and preanal fin length (pre-AFL). Although there were significant differences between morphometric characteristics (post-AFL, post-DFL, pre-AFL) and total length, no significant differences were found in the VMC. These average ratios were determined as pre-AFL to TL 0.61 ♀, 0.71 ♂; post-AFL to TL 0.72 ♀, 0.84 ♂; post-DFL to TL 0.68 ♀, 0.81 ♂, respectively. The aim of this study was to investigate if sexual differences could affect external morphology in cultured seabass and, additionally, to determine sexual dimorphism related to morphological differences during the maturation and spawning seasons in this species.

Our study reports the first data on mercury (Hg) isotope composition in marine European fish, for seven distinct populations of the European seabass, Dicentrarchus labrax. The use of δ 202 Hg and Δ 199 Hg values in SIBER enabled us to estimate Hg isotopic niches, successfully discriminating several populations. Recursive-partitioning analyses demonstrated the relevance of Hg stable isotopes as discriminating tools. Hg isotopic values also provided insight on Hg contamination sources for biota in coastal environment. The overall narrow range of δ 202 Hg around Europe was suggested to be related to a global atmospheric contamination while δ 202 Hg at some sites was linked either to background contamination, or with local contamination sources. Δ 199 Hg was related to Hg levels of fish but we also suggest a relation with ecological conditions. Throughout this study, results from the Black Sea population stood out, displaying a Hg cycling similar to fresh water lakes. Our findings bring out the possibility to use Hg isotopes in order to discriminate distinct populations, to explore the Hg cycle on a large scale (Europe) and to distinguish sites contaminated by global versus local Hg source. The interest of using Hg sable isotopes to investigate the whole European Hg cycle is clearly highlighted.

The Barfray project aimed at improving the knowledge on the essential habitats of the European sea bass (Dicentrachus labrax) on the French Atlantic coast (English Channel and Bay of Biscay). One of the research need concerns the diversity of feeding areas contributing to the main spawning grounds. Here we present the analysis of the diffusion of tagged individuals towards the feeding areas, which follows a pilot operation of conventional tagging on spawning grounds. As of 25/03/2021, twenty-six recaptures had been recorded, corresponding to a recapture rate of 8.1%. The diffusion of the fish is rather rapid from the Gironde to the tip of Brittany (Pointe du Raz), although the fish had been tagged in a relatively coastal area. The coastal location of the tagging site raises the question of whether the tagged fish were spawning or not. From a methodological point of view, the number of recaptures is too low to be able to draw conclusions on the type of tag to be preferred. Regarding ...

The Barfray project aimed at improving the knowledge on the essential habitats of the European sea bass (Dicentrachus labrax) on the French Atlantic coast (English Channel and Bay of Biscay). One of the research need concerns the diversity of feeding areas contributing to the main spawning grounds. Here we present the setting up of a conventional tagging pilot operation on spawning ground, a prerequisite to carry out this research. The operation initially aimed to tag 2,000 adult sea bass by mobilising a pair of pelagic trawlers for 10 days of fishing on an offshore spawning ground in the Bay of Biscay. This operation had to be reorganised and reduced in duration as no pelagic trawlers agreed to participate. Ifremer therefore carried out a sea bass spawning tagging campaign with the help of two longliners from La Cotinière (Oléron Island) from 20 to 24 February 2019 off the Gironde. This campaign allowed the tagging of 321 adult sea bass with one or two external tags. The weather co...

The relationships among 15 morphometric measurements in 219 aliquots of European seabass (Dicentrarchus labrax) were examined with respect to sexual dimorphism. The ratio of females to males was determined as 1:5.1 and gonadosomatic indices (%) were found for males (2.13 ± 0.86) and females (3.63 ± 1.18). There were 4 morphometric characteristics that differed between genders: ventral margin of cleithrum (VMC), postanal fin length (post-AFL), postdorsal fin length (post-DFL), and preanal fin length (pre-AFL). Although there were significant differences between morphometric characteristics (post-AFL, post-DFL, pre-AFL) and total length, no significant differences were found in the VMC. These average ratios were determined as pre-AFL to TL 0.61 ♀, 0.71 ♂; post-AFL to TL 0.72 ♀, 0.84 ♂; post-DFL to TL 0.68 ♀, 0.81 ♂, respectively. The aim of this study was to investigate if sexual differences could affect external morphology in cultured seabass and, additionally, to determine sexual dimorphism related to morphological differences during the maturation and spawning seasons in this species.

Infectious diseases and fish feeds management are probably the major expenses in the aquaculture business. Hence, it is a priority to define sustainable strategies which simultaneously avoid therapeutic procedures and reinforce fish immunity. Currently, one preferred approach is the use of immunostimulants which can be supplemented to the fish diets. Arginine is a versatile amino acid with important mechanisms closely related to the immune response. Aiming at finding out how arginine affects the innate immune status or improve disease resistance of European seabass (Dicentrarchus labrax) against vibriosis, fish were fed two arginine-supplemented diets (1% and 2% arginine supplementation). A third diet meeting arginine requirement level for seabass served as control diet. Following 15 or 29 days of feeding, fish were sampled for blood, spleen and gut to assess cell-mediated immune parameters and immune-related gene expression. At the same time, fish from each dietary group were chall...

The present work aimed to study the role of dietary tryptophan supplementation in modulating the European seabass (Dicentrarchus labrax) immune condition during stressful rearing conditions (i.e., 15 days exposure to high density), as well as the immune response to acute inflammation after intraperitoneal injection of a bacterial pathogen. Stress alone did not compromise seabass health indicators. In contrast, a clear peripheral and local inflammatory response was observed in response to the inoculated bacteria. Moreover, exposure to a high stocking density seemed to exacerbate the inflammatory response at early sampling points, compared to fish stocked at a lower density. In contrast, stressed fish presented some immune-suppressing effects on the T-cell surface glycoprotein receptor expressions at a late sampling point following inflammation. Regarding the effects of dietary tryptophan, no changes were observed on seabass immune indicators prior toinflammation, while a small number of immunosuppressive effects were observed in response to
inflammation, supporting tryptophan’s role in the promotion of immune-tolerance signals during in-flammation. Nonetheless, tryptophan dietary supplementation improved the inflammatory response against a bacterial pathogen during stressful conditions, supported by a reduction of plasma cortisol levels, an up-regulation of several immune-related genes at 48 h, and an inversion of the previously observed, stress-induced T-cell suppression. Finally, the involvement of tryptophan catabolism in macrophages was confirmed by the up-regulation of genes involved in the kynurenine pathway. The present study brings new insights regarding the immune modulatory role of tryptophan during stressful conditions in fish, thus allowing for the development of novel prophylactic protocols during vaccination by intraperitoneal injection in the European seabass.

Infectious diseases and fish feeds management are probably the major expenses in the aquaculture business. Hence, it is a priority to define sustainable strategies which simultaneously avoid therapeutic procedures and reinforce fish immunity. Currently, one preferred approach is the use of immunostimulants which can be supplemented to the fish diets. Argi-nine is a versatile amino acid with important mechanisms closely related to the immune response. Aiming at finding out how arginine affects the innate immune status or improve disease resistance of European seabass (Dicentrarchus labrax) against vibriosis, fish were fed two arginine-supplemented diets (1% and 2% arginine supplementation). A third diet meeting arginine requirement level for seabass served as control diet. Following 15 or 29 days of feeding, fish were sampled for blood, spleen and gut to assess cell-mediated immune parameters and immune-related gene expression. At the same time, fish from each dietary group were challenged against Vibrio anguillarum and survival was monitored. Cell-mediated immune parameters such as the extracellular superoxide and nitric oxide decreased in fish fed arginine-supplemented diets. Interleukins and immune-cell marker transcripts were down-regulated by the highest supplementation level. Disease resistance data were in accordance with a generally depressed immune status, with increased susceptibility to vibriosis in fish fed arginine supplemented diets. Altogether, these results suggest a general inhibitory effect of arginine on the immune defences and disease resistance of European seabass. Still, further research will certainly clarify arginine immunomodulation pathways thereby allowing the validation of its potential as a prophylactic strategy.