Flatfish Species Research Articles

Evaluation of toxic metal contaminants in the demersal flatfishes (Order: Pleuronectiformes) collected from a marine biosphere reserve

In this study, we have evaluated the concentrations of heavy metals (Cu, Zn, Cd, and Pb) in 24 flatfish species (Order: Pleuronectiformes) collected from the Gulf of Mannar Biosphere Reserve, Tamil Nadu, India. All four metals were recorded in all flatfishes except for lead which was below detection limits in nine species. The order of metal concentrations in the flatfishes is Zn > Cu > Pb > Cd. Bioaccumulation factor (BAF), principal component analysis (PCA), and hierarchical cluster analysis (HCA) were carried out. BAFs of different metals follow the order Cd > Zn > Cu > Pb. A firm positive correlation was observed between the metal concentrations among the tissues of different flatfishes. PCA and HCA indicate that the metals originated mostly from the manmade activities. These heavy metals sink to the sediments of the sea floor and are bioaccumulated in the bottom-dwelling flatfishes. Continued surveillance of metal concentrations in sediments and flatfishes should be conducted to remediate the metal pollution effectively.

Vague labelling laws and outdated fish naming lists undermine seafood market transparency in Canada

Despite the expressed interest of Canadians in sustainable and comprehensively labelled seafood, the country’s seafood labelling requirements remain scant and naming conventions in the Canadian Food Inspection Agency (CFIA) ‘fish list’ allow the grouping of multiple species under single ‘umbrella’ terms. Here, we test the extent to which CFIA listings reflect current market availability and conceal biodiversity, using the flatfishes as a model. Accordingly, we compared CFIA-listed flatfish species with those documented in Canadian import records, those in production records of Canada and its flatfish suppliers, as well as those identified in DNA-based market surveys conducted across Canada. Of the 43 flatfish species on the CFIA list, only three have consistently shown up in Canadian imports, production records and market surveys, whereas almost a third (n = 15) failed to appear in any of the latter over at least a decade. Species have been detected on the market that are absent from this list, while overfished and/or threatened taxa have been found concealed under vague generic terms. The list’s many superfluous inclusions, outdated names, missing species and poor correspondence with trading partner’s naming conventions are inconsistent with the legal tenets of Canadian policy to uphold fair market practices and consumer choice, and instead result in a system inundated by numerous paths of misinterpretation, misclassification and substitution. Moreover, Canada’s official flatfish trade statistics lack sufficient taxonomic granularity to elucidate all species involved and track flatfish trade flows. Illuminating these loopholes should compel improvements in Canadian seafood labelling and traceability legislative frameworks.

Flatfish may be underestimated in the diet of gray seals (Halichoerus grypus)

The United States east coast population of the gray seal (Halichoerus grypus (Fabricius, 1791)) was once hunted to near extirpation, but the population has since rebounded due to protection by the Marine Mammal Protection Act of 1972. Although this population growth is seen as a success by conservationists, others are concerned about the economic and ecological impact of gray seals on New England fisheries. The study objective was to quantify flatfish presence in the diet of gray seals using an analysis of prey DNA in seal scat (molecular scatology). This may reduce a potential bias in other diet analysis methods since flatfish may not be swallowed whole, and therefore, their identifying otoliths may not be present. Scats were collected from Muskeget and Monomoy islands off Cape Cod, Massachusetts, USA, in 2016, 2017, and 2018 and analyzed for flatfish presence using species-specific polymerase chain reaction (PCR) assays and a hard parts analysis using otoliths. Frequency of occurrence for flatfish species from DNA was higher than estimated in previous literature on gray seal diet and a concurrent otolith analysis of the same samples, suggesting that previous analyses may have potentially underestimated the importance of flatfish in the diet.

Causal links between North Sea fish biomass trends and seabed structure

Distinct areas of seabed, called seascapes, are known to shape benthic habitats and communities, yet little is known about the extent to which they affect the dynamics of marine fish populations. We explored the relationship between seascapes and trends in the biomass density of several North Sea fish species. We divided the North Sea into 10 seascapes using standardized methods. Time series of fish biomass density were derived from the North Sea International Bottom-Trawl Survey (NS-IBTS) and aggregated to the seascape level. We analysed the interdependencies between these time series using a causal association network and found independent biomass density trends between adjacent seascapes at a time interval of 0 yr in all species assessed. Long-term causal dependencies in biomass density occurred at time lags of 1-2 yr across different gradients of exchange: (1) both directions from North to South; (2) unidirectional, North-South; (3) unidirectional, South-North; (4) unidirectional, East-West; and (5) no clear direction. Our findings indicate that the separation in (a)biotic conditions between North Sea seascapes can represent relevant barriers to the processes determining the observed fish biomass density. We found that non-fusiform morphology and demersal habitat preferences best explained short-term causal dependencies. This combination is particular to the flatfish and ray species included in the present study. Contrarily, the movement of large, long-lived, benthopelagic species best explained long-term causal dependencies. Our work highlights how causal association networks can be used to study the temporal dependencies between spatial time series in ecology.

Greater exposure of nearshore habitats in the Bering Sea makes fish early life stages vulnerable to climate change

Marine fish species with complex life cycles undergo ontogenetic changes in their physiological and habitat requirements. Therefore, predicting how warming ocean conditions are likely to impact fish populations requires size-(age-) and habitat-specific analyses. We determined the habitat exposure and scope of adaptability of 4 shelf-oriented flatfish species in the Bering Sea to projected climate-driven warming. We quantified present day and end-of-century habitat exposure based on hindcasts and forecasts of regional ocean circulation models and quantified fish adaptability based on changes in depth distribution and from published thermal tolerances of northern rock sole Lepidopsetta polyxystra, yellowfin sole Limanda aspera, Alaska plaice Pleuronectes quadrituberculatus, and flathead sole Hippoglossoides elassodon. These 4 species complete their life cycle within the Bering Sea shelf but have different depth preferences and thermal tolerances throughout ontogeny. We found that species or size ranges that occupy the inner shelf, such as northern rock sole, yellowfin sole, and Alaska plaice, are exposed to higher seasonal variability compared to outer shelf species. While these inner shelf species are likely adapted to large seasonal changes in temperature, the future range of seasonal variability was projected to exceed their thermal tolerances. Therefore, we expect species that reside inshore during part of their life cycle and have high temperature sensitivity and limited mobility to be particularly vulnerable to climate change.

Influence of temperature on growth and survival of juvenile winter flounder, Pseudopleuronectes americanus (Walbaum) reared under continuous light

AbstractWinter flounder, Pseudopleuronectes americanus, has emerged as a promising candidate flatfish for cold‐water aquaculture and restocking. Here, juveniles were reared for 8 weeks at three temperatures: 10, 15, and 20°C under 24‐hr light. All fish were imaged at stocking and at 2‐week intervals, where growth was measured as changes in standard length (SL) and body area (BA). By week 2, fish reared at 15 and 20°C were larger than those grown at 10°C. At weeks 4 to 6, fish at 15°C were larger than fish at 20°C. Linear regressions were used to model growth dynamics over time at each temperature. Highly significant linear growth trajectories were detected over time for SL and BA. SL and BA regressions also showed a significant difference among the slopes across temperatures, where comparing slopes showed the best temperature to rear the flounder was 15°C. Weights of fish held at 15°C and 20°C were greater than at 10°C at the termination of the experiment. Within each temperature, the growth rate of malpigmented fish was not different from that of the normally pigmented fish. Overall, growth of winter flounder was comparable to that of other commercially produced flatfish species, providing strong evidence for this flatfish species as a potential species for aquaculture.

Development of whole-genome multiplex assays and construction of an integrated genetic map using SSR markers in Senegalese sole

The Senegalese sole (Solea senegalensis) is an economically important flatfish species. In this study, a genome draft was analyzed to identify microsatellite (SSR) markers for whole-genome genotyping. A subset of 224 contigs containing SSRs were preselected and validated by using a de novo female hybrid assembly. Overall, the SSR density in the genome was 886.7 markers per megabase of genomic sequences and the dinucleotide motif was the most abundant (52.4%). In silico comparison identified a set of 108 SSRs (with di-, tetra- or pentanucleotide motifs) widely distributed in the genome and suitable for primer design. A total of 106 markers were structured in thirteen multiplex PCR assays (with up to 10-plex) and the amplification conditions were optimized with a high-quality score. Main genetic diversity statistics and genotyping reliability were assessed. A subset of 40 high polymorphic markers were selected to optimize four supermultiplex PCRs (with up to 11-plex) for pedigree analysis. Theoretical exclusion probabilities and real parentage allocation tests using parent–offspring information confirmed their robustness and effectiveness for parental assignment. These new SSR markers were combined with previously published SSRs (in total 229 makers) to construct a new and improved integrated genetic map containing 21 linkage groups that matched with the expected number of chromosomes. Synteny analysis with respect to C. semilaevis provided new clues on chromosome evolution in flatfish and the formation of metacentric and submetacentric chromosomes in Senegalese sole.

An improved de novo assembling and polishing of Solea senegalensis transcriptome shed light on retinoic acid signalling in larvae

Senegalese sole is an economically important flatfish species in aquaculture and an attractive model to decipher the molecular mechanisms governing the severe transformations occurring during metamorphosis, where retinoic acid seems to play a key role in tissue remodeling. In this study, a robust sole transcriptome was envisaged by reducing the number of assembled libraries (27 out of 111 available), fine-tuning a new automated and reproducible set of workflows for de novo assembling based on several assemblers, and removing low confidence transcripts after mapping onto a sole female genome draft. From a total of 96 resulting assemblies, two “raw” transcriptomes, one containing only Illumina reads and another with Illumina and GS-FLX reads, were selected to provide SOLSEv5.0, the most informative transcriptome with low redundancy and devoid of most single-exon transcripts. It included both Illumina and GS-FLX reads and consisted of 51,348 transcripts of which 22,684 code for 17,429 different proteins described in databases, where 9527 were predicted as complete proteins. SOLSEv5.0 was used as reference for the study of retinoic acid (RA) signalling in sole larvae using drug treatments (DEAB, a RA synthesis blocker, and TTNPB, a RA-receptor agonist) for 24 and 48 h. Differential expression and functional interpretation were facilitated by an updated version of DEGenes Hunter. Acute exposure of both drugs triggered an intense, specific and transient response at 24 h but with hardly observable differences after 48 h at least in the DEAB treatments. Activation of RA signalling by TTNPB specifically increased the expression of genes in pathways related to RA degradation, retinol storage, carotenoid metabolism, homeostatic response and visual cycle, and also modified the expression of transcripts related to morphogenesis and collagen fibril organisation. In contrast, DEAB mainly decreased genes related to retinal production, impairing phototransduction signalling in the retina. A total of 755 transcripts mainly related to lipid metabolism, lipid transport and lipid homeostasis were altered in response to both treatments, indicating non-specific drug responses associated with intestinal absorption. These results indicate that a new assembling and transcript sieving were both necessary to provide a reliable transcriptome to identify the many aspects of RA action during sole development that are of relevance for sole aquaculture.

A holistic investigation of tracers at population and individual scales reveals population structure for the common sole of the Eastern English Channel

The sustainable exploitation of sea resources is based on the understanding of population distribution, structure and functioning. The mismatch between stock units and fish populations can dramatically bias the assessment and lead to irrelevant or even detrimental management measures. The common sole of the Eastern English Channel (EEC; ICES division VIId) is a flatfish species of high interest that has been overexploited over the last decades. Low connectivity induced by early life stages across the stock was previously known, but gaps remained regarding the role of adults in population connectivity and spatial structure. In this study we have filled these gaps by (1) gathering all the information on stock identity through five population- and individual-based approaches, and (2) combining this information in a semi-quantitative framework, i.e. the Stock Differentiation Index (SDI). Regarding the population-based approaches, growth and abundance-at-age analyses highlighted a lasting signal of population structure, with three population subunits. Regarding the individual-based approaches, genetic analysis highlighted low but significant genetic differentiation between the three subunits over an evolutionary time scale. Besides, a mark-recapture study demonstrated a low level of exchange between these subunits. Finally, an analysis of otolith shape pinpointed spatial variation between the three subunits. Overall, the SDI = 0.93 suggested evidence of spatial structure. The misalignment of the current stock definition with the underlying biological metapopulation now requires the improvement of the assessment-management to ensure its sustainable exploitation.

Reconciling seascape genetics and fisheries science in three codistributed flatfishes.

Uncertainty hampers innovative mixed‐fisheries management by the scales at which connectivity dynamics are relevant to management objectives. The spatial scale of sustainable stock management is species‐specific and depends on ecology, life history and population connectivity. One valuable approach to understand these spatial scales is to determine to what extent population genetic structure correlates with the oceanographic environment. Here, we compare the level of genetic connectivity in three codistributed and commercially exploited demersal flatfish species living in the North East Atlantic Ocean. Population genetic structure was analysed based on 14, 14 and 10 neutral DNA microsatellite markers for turbot, brill and sole, respectively. We then used redundancy analysis (RDA) to attribute the genetic variation to spatial (geographical location), temporal (sampling year) and oceanographic (water column characteristics) components. The genetic structure of turbot was composed of three clusters and correlated with variation in the depth of the pycnocline, in addition to spatial factors. The genetic structure of brill was homogenous, but correlated with average annual stratification and spatial factors. In sole, the genetic structure was composed of three clusters, but was only linked to a temporal factor. We explored whether the management of data poor commercial fisheries, such as in brill and turbot, might benefit from population‐specific information. We conclude that the management of fish stocks has to consider species‐specific genetic structures and may benefit from the documentation of the genetic seascape and life‐history traits.

Characterization of a novel spexin gene (spx2) in the half-smooth tongue sole and regulation of its expression by nutritional status

Spexin (SPX) is a newly identified peptide hormone of 14 amino acids (aa) with pleiotropic functions in vertebrates, and recently a second paralog of SPX (named SPX2) has been only found in some non-mammalian species (the previous form of SPX is now designated as SPX1). Results of previous studies have revealed the existence of a functional SPX1 in the half-smooth tongue sole. To clarify the divergence of the spexin family, we further isolated the spx2 gene from the same flatfish species in the current study. The open reading frame of tongue sole spx2 was 378 nucleotides in size that encoded a 125-aa preprohormone, and the tongue sole SPX2 precursor included a 17-aa mature peptide that may be amidated at the C-terminus, rather than a tetradecapeptide reported in most other vertebrates. Tissue distribution analysis showed that spx2 transcripts were found in a wide array of tissues of both sexes with the highest expression in the ovary. In addition, the spx2 mRNA abundance was also ubiquitously detected in different brain regions. Food deprivation for 4 weeks stimulated spx2 mRNA levels at the brain-pituitary-ovary axis, and refeeding of starved fish restored the spx2 mRNA levels back to normal. Taken together, this study provides initial evidence for the existence of a novel spexin gene (spx2) in Pleuronectiformes and suggest its possible involvement in the regulation of energy balance in the female tongue sole.

Only a few key prey species fuel a temperate coastal fish food web

The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are present in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.

Efficiency changes in bottom trawling for flatfish species as a result of the replacement of mechanical stimulation by electric stimulation

AbstractAlthough fishing with electricity is illegal in the European Union, a number of temporary licences allowed converting beam trawlers to pulse trawling. To analyse how the adaption of pulse trawling changed this fishery, we studied fishing speeds and landings per unit effort as proxies for catch efficiencies for the main target species. Compared to conventional tickler chain beam trawls, pulse trawls were towed at lower speeds (small vessels −10%, large vessels −23%). Large vessels that switched from conventional beam trawls to pulse trawls at the end of 2009 gradually increased catch efficiency for sole over the period of almost 1 year. While pulse trawling was found to have higher catch rates (kg/h) for sole (small vessels +74%, large vessels +17%), lower catch rates were observed for plaice (small vessels −31%, large vessels −32%). Vessels that switched later achieved immediate gains in catch efficiency for sole. The change in catch efficiency is likely due to the difference in cramp response between the species.

Population genetic structure of turbot (Scophthalmus maximus L., 1758) in the Black Sea.

Turbot, Scophthalmus maximus, is a commercially important demersal flatfish species distributed throughout the Black Sea. Several studies performed locally with a limited number of specimens using both mitochondrial DNA (mtDNA) and microsatellite markers evidenced notable genetic variation among populations. However, comprehensive population genetic studies are required to help management of the species in the Black Sea. In the present study eight microsatellite loci were used to resolve the population structure of 414 turbot samples collected from 12 sites across the Black Sea. Moreover, two mtDNA genes, COI and Cyt-b, were used for taxonomic identification. Microsatellite markers of Smax-04 and B12-I GT14 were excluded from analysis due to scoring issues. Data analysis was performed with the remaining six loci. Loci were highly polymorphic (average of 17.8 alleles per locus), indicating high genetic variability. Locus 3/20CA17, with high null allele frequency (>30%), significantly deviated from HW equilibrium. Pairwise comparison of the FST index showed significant differences between most of the surveyed sampling sites (P < 0.01). Cluster analysis evidenced the presence of three genetic groups among sampling sites. Significant genetic differentiation between Northern (Sea of Azov and Crimea) and Southern (Turkish Black Sea Coast) Black Sea sampling sites were detected. The Mantel test supported an isolation by distance model of population structure. These findings are vital for long-term sustainable management of the species and development of conservation programs. Moreover, generated mtDNA sequences would be useful for the establishment of a database for S. maximus.

Flatfish (Pleuronectiformes) species richness and depth distribution in the Gulf of Nicoya, Golfo Dulce, and two adjacent areas on the Pacific coast of Costa Rica

Abstract: Flatfish diversity and depth distribution in the Gulf of Nicoya, Golfo Dulce, and two adjacent areas on the Pacific coast of Costa Rica. Introduction. Information on flatfish diversity and depth distribution is scarce for the Eastern Tropical Pacific. Historical data is important to evaluate changes in ecosystems due to local, regional and global stressors. Objective. To provide information on the presence, depth distribution and lengths of flatfish species collected by trawl nets. Methods. Fish studies were conducted by trawling at four sites along the Pacific coast of Costa Rica by the survey vessels Skimmer (1979-1989), Nishin Maru (1987-1988) and Victor Hensen (1993-1994). The published lists of species were consulted, museum specimens were accessed, and a list of flatfishes assembled. Results. A total of 36 species were found at the four sites over a depth range of 8 to 359 m. The family Paralichthyidae included 13 species followed by the Cynoglossidae with 12 species. Achiridae had six and Bothidae had five. The most speciose genus was Symphurus with 12 species. Thirty-five species were collected at depths from 10 to 235 m in the Gulf of Nicoya and Golfo Dulce. The Gulf of Nicoya estuary yielded 27 species during the Skimmer expedition and over a depth range of 8 to 60 m, while 31 species were found there during the V. Hensen survey at depths from 10 to 228 m. The V. Hensen survey in Golfo Dulce (20 to 235 m) captured 19 species, and 17 in Coronado Bay (21 to 187 m). Off the Nicoya Peninsula (56 to 359 m) 13 species were collected by the Nishin Maru shrimp trawler. A total of 21 species (58 %) were found at depths greater than 100 m and were probably exposed the low oxygen concentrations characteristic of hypoxia. During the V. Hensen survey Symphurus chabanaudi and S. elongatus were captured more frequently in the Gulf of Nicoya, while S. leei was so in Golfo Dulce. Cluster analyses based on presence-absence data for the Gulf of Nicoya and Golfo Dulce revealed low station similarity indicating habitat partitioning among the species. The size (Total length) of 33 species measured from both the Gulf of Nicoya and Golfo Dulce ranged from 8 cm (Syacium cf longidorsale, Trinectes xanthurus) to 50 cm (S. ovale). Only 12 species were found with lenghts over 20 cm. Of the species collected, A. mazatlanus (30 cm) and S. ovale (50) appear to be length records for the region. Data on flatfish landings by the semi-industrial fishing fleet for the period 2000-2016 indicates that this group represents less than 1% of the total landings (shrimp and bycatch), with a minimum of 365 kg in 2001 and a maximum of 13.414 kg in 2013. Conclusions. The diversity of the flatfish fauna of the Pacific coast of Costa Rica appears relatively high but comparable to that found in other tropical regions. The number of trawling ships has declined significantly on the Pacific coast of Costa Rica after 2014. This reduced fishing impact on the populations provides a good opportunity for updating the trophic models available for both the Gulf of Nicoya and Golfo and their use as tools for better management of the ecosystems.

The Teleost Thymus in Health and Disease: New Insights from Transcriptomic and Histopathological Analyses of Turbot, Scophthalmus maximus.

The thymus is a primary lymphoid organ that plays a pivotal role in the adaptive immune system. The immunobiology of the thymus in fish is considered to be similar to that of mammals, but it is actually poorly characterized in several cultured teleost species. In particular, while investigations in human and veterinary medicine have highlighted that the thymus can be affected by different pathological conditions, little is known about its response during disease in fish. To better understand the role of the thymus under physiological and pathological conditions, we conducted a study in turbot (Scophthalmus maximus), a commercially valuable flatfish species, combining transcriptomic and histopathological analyses. The myxozoan parasite Enteromyxum scophthalmi, which represents a major challenge to turbot production, was used as a model of infection. The thymus tissues of healthy fish showed overrepresented functions related to its immunological role in T-cell development and maturation. Large differences were observed between the transcriptomes of control and severely infected fish. Evidence of inflammatory response, apoptosis modulation, and declined thymic function associated with loss of cellularity was revealed by both genomic and morphopathological analyses. This study presents the first description of the turbot thymus transcriptome and provides novel insights into the role of this organ in teleosts’ immune responses.

Effect of Halomonas storage poly‐β‐hydroxybutyrates on survival, growth and vibriosis resistance of half‐smooth tongue sole Cynoglossus semilaevis juveniles

Half-smooth tongue sole Cynoglossus semilaevis is a high-value marine fish species. The intensive farming of this flatfish species has been suffered from disease outbreak. Poly-β-hydroxybutyrate (PHB) is a carbon storage compound accumulated by a wide variety of prokaryotes and is considered biocontrol agent applied in aquaculture. In this study, the dietary effect of PHB-accumulating Halomonas (HM.PHB) was investigated on survival, growth, resistance on Vibrio anguillarum and intestine microbial composition of C. semilaevis juveniles. Halomonas was fermented, which contained 76% PHB on cell dry weight. The fish juveniles were fed formulated feeds containing 1% HM.PHB, 3% HM.PHB and 5% HM.PHB, and 3% particle PHB (Par.PHB) and 3% Halomonas containing no PHB (HM) for 6 weeks. The basal feed feeding was considered as the control. The results revealed that both Halomonas-PHB and particle PHB significantly improved the survival and growth of the juveniles than the control (p < .05), while HM was in between. When challenged with V. anguillarum, the survival rate in 1% HM.PHB, 3% HM.PHB and 5% HM.PHB was significantly improved than the control. Moreover, the increased intestine fold, epithelium height and surface were also observed in 3% HM.PHB. PCoA based on high-throughput sequencing of 16S rRNA gene fragment indicated that dietary Halomonas-PHB and particle PHB modified and stabilized the intestine microbial community of the fish. Our study demonstrated that Halomonas-PHB is an effective feed additive for C. semilaevis juvenile culture. The outcome of this study facilitates the application of Halomonas-PHB in C. semilaevis and other marine fish aquaculture.

Relating groundfish diversity and biomass to deepsea corals and sponges using trawl survey catch data

Deep-sea corals and sponges (DSCS) inhabit the world’s oceans and are often associated with high fish abundance. However, the precise nature and extent of any association is difficult to quantify and remains poorly understood. We investigated associations between DSCS and demersal fish using data from the Northwest Fisheries Science Center’s bottom trawl survey (2003-2015). General linear mixed models showed that average species density of groundfish was slightly higher and groundfish biomass slightly lower in tows with DSCS. Multivariate analyses were used to examine relationships among fish community structure, DSCS biomass, and environmental parameters (depth, latitude, bottom temperature). No strong correlations occurred between the community structure of groundfish and DSCS biomass; instead, bottom temperature and depth were the primary drivers of community composition. However, indicator species analysis also showed various species-specific associations with DSCS. Specifically, some flatfish species exhibited relationships with coral and sea pen biomass, whereas some rockfishes were associated with high sponge biomass. Our results provide information on the broad-scale associations among DSCS and demersal fishes that may be useful for developing studies focused on the functional value of DSCS as essential fish habitat and the role they play in groundfish life history and ecology.

Dietary bioaccumulation of persistent organic pollutants in the common sole Solea solea in the context of global change. Part 2: Sensitivity of juvenile growth and contamination to toxicokinetic parameters uncertainty and environmental conditions variability in estuaries

The amount of potentially toxic chemicals in a fish depends on various environmental factors, such as temperature and feeding ecology, which can be affected by Global Changes (GC). The main objective of the present work was to study the relative influence of temperature, food quality and food availability on the growth and contamination of juveniles of common sole (Solea solea), a marine flatfish species known to be a relevant indicator of the nursery quality. It focuses on two Persistent Organic Pollutants (CB153 and L-PFOS) of legacy and emerging concern, respectively. To achieve this, we used a toxicokinetic (TK) model in which toxicant flows are mechanistically predicted using a bioenergetic model based on the Dynamic Energy Budget (DEB) theory. This modelling framework was applied to juvenile sole from the Gironde estuary (SW France) and allows accounting for the influence of environmental conditions on fish biological processes involved in toxicant fluxes. To compare their respective influence on model predictions of age, length, and contamination at puberty, we included in a global sensitivity analysis: (1) environmental variability gathered from literature for this particular estuary and (2) TK parameters (i.e. assimilation efficiency AE and elimination rate k˙e) variability and uncertainty gathered from literature about each contaminant but for different fish species and experimental conditions. Then, model predictions were confronted to fish contamination measurements from the Gironde Estuary with different combinations of TK parameter values from literature. Results highlighted a key role of diet composition on fish contamination and growth while water temperature only affected growth. It stressed the need to focus on GC impact on benthic communities and their consequences on juvenile fish diet for future work on GC scenarios. Furthermore, for both chemical, the range of variability of TK parameters from experiments led to underestimated fish contaminations. The best model fits were obtained using TK parameter values from model applications: from Mounier et al. (n.d.) for CB153 (Solea solea, experiment, AE=0.8 and k˙e=0 d−1) and from de Vos et al. (2008) for PFOS (food chain of the Western Scheldt estuary, The Netherlands, AE=0.8 and k˙e=0.8 10−2.d−1).

Novel insights into the selective breeding for disease resistance to vibriosis by using natural outbreak survival data in Chinese tongue sole (Cynoglossus semilaevis)

As an important farmed flatfish species, Chinese tongue sole (Cynoglossus semilaevis) is heavily threatened by vibriosis in recent years. Genetic selection for disease resistance is a sustainable and effective approach to reduce frequent outbreaks. To verify whether the resistance of vibriosis (caused by co-infections of different Vibrio spp. in natural outbreak) can be included in breeding programs, in this study, genetic analysis of resistance to vibriosis based on natural outbreak survival data was carried out by using four statistical models (three cross-sectional models and one longitudinal model). The magnitude of the genetic variation in the resistance of vibriosis was estimated through a 56-day natural outbreak test of 15,912 individuals from 78 full-sib families (the offspring of 77 sires and 78 dams). Variance components and heritabilities were estimated at two cut-off points respectively, i.e. day 35 with 49.2% cumulative mortality and day 56 with 71.6% finial cumulative mortality. Heritabilities of resistance to vibriosis were low to moderate, where values at day 56 (0.04–0.21) were significantly different from zero, while values at day 35 (0.03–0.10) were not significantly different from zero in each corresponding model. The Spearman rank correlations between family EBVs for different models were high (> 0.98), indicating a nearly identical ranking of families. Compare to three simpler cross-section models, the longitudinal model taken the time until death into account demonstrated the highest accuracy of family selection. These results confirmed the existence of genetic variation for resistance to vibriosis and provided novel insights into the selective breeding for disease resistance to vibriosis by using natural outbreak survival data in tongue sole.