First assessment of Rare Earth Element organotropism in Solea solea in a coastal area: The West Gironde Mud Patch (France).

Few studies exist on concentration and internal distribution of Rare Earth Elements (REEs) in marine fishes. REEs organotropism was determined in common sole (Solea solea) from the West Gironde Mud Patch (WGMP; N-E Atlantic Coast, France). The highest ∑REEs concentrations occurred in liver (213 ± 49.9 µg kg-1 DW) and gills (119 ± 77.5 µg kg-1 DW) followed by kidneys (57.7 ± 25.5 µg kg-1 DW), whereas the lowest levels were in muscles (4.53 ± 1.36 µg kg-1 DW) of Solea solea. No significant age- or sex-related differences were observed. The organotropism varied among groups of REEs. Light and heavy REEs preferentially accumulated in liver and gills, respectively. All considered organs showed different normalized REEs patterns, suggesting differences in internal distribution processes between organs. Further work should address: (1) baseline levels worldwide, and (2) factors controlling uptake and organ-specific concentration of REEs.

Morphological, ultrastructural, and molecular characterization of Livoneca redmanii (Leach, 1818) (Isopoda: Cymothoidae) infestation among Solea solea.

In the present investigation, we identified a cymothoid isopod species, Livoneca redmanii (Isopoda, Cymothoidae), in the branchial cavity, skin, and muscle pouch of the common sole (Solea solea) (Soleidae, Pleuronectiformes) from Qarun Lake, Egypt. The parasite was identified by morphometric and ultrastructural analysis, and molecular typing of the 16S rRNA gene. Out of 625 S. solea specimens collected, 8.16% were infested with the isopod. For the first time, the ultrastructural features of L. redmanii in different growth stages were described, revealing the fine characteristics of the body appendages, the eyes, the antennae, and the antennules of the female, male, and juvenile isopod, as well as the external layers of the ova. Additionally, the detailed structures of the mouth parts, the sensory microtriches, and the male organs (penis, appendex masculine, and the genital furrow) were elucidated. A histological examination of the infested gill revealed damaged gill lamellae, leukocyte infiltration, and epithelial hyperplasia. Besides, microscopic examination of the skin showed focal erosion and periodic acid stain-positive foci in the dermis. Phylogenetic analysis revealed the close relationship between the L. redmanii isolated in this study and those recovered from mugiliid fry in the Mediterranean Sea in 2017. Based on our findings, we recommend using hatchery-reared fry instead of wild fry for supplying lakes and fish farms. Also, a strict biosecurity program must be implemented to avoid the transmission and spread of these disease-causing parasites.

Spatiotemporal accumulation of fatal pharyngeal entrapment of flatfish in harbour porpoises (Phocoena phocoena) in the German North Sea.

The evolution of a permanent separation of the upper respiratory and digestive tract is one of the adaptions cetaceans evolved for their aquatic life. Generally, it prevents odontocetes from choking on either saltwater or foreign bodies during ingestion under water. Nevertheless, several sporadic single case reports from different parts of the world show that this separation can be reversed especially by overly large items of prey. This incident can have a fatal outcome for the odontocetes. The German federal state of Schleswig-Holstein has a year-round, permanent and systematic stranding network that retrieves stranded marine mammals from its shorelines and constantly enables post-mortem examinations. In 2016, with nine affected animals, a high incidence of fatal pharyngeal entrapment of flatfish in harbour porpoises (Phocoena phocoena) occurred during spring and early summer on the German North Sea island of Sylt. All flatfish were identified as common sole (Solea solea). A retrospective post-mortem data analysis over a 30-year period from the North and Baltic Sea revealed similar yearly and seasonally case accumulations on the same island in the 1990s as well as several single case events over the whole timespan. All cases except one were caused by flatfish. When flatfish speciation was performed, only common sole was identified. From 1990 to 2019, of all examined harbour porpoises, 0.3% (2/713) from the Baltic Sea and 5.5% (45/820) from the North Sea died due to fish entrapped in the pharynx. On the North Sea coast, the occurrence of fatal obstruction shows high yearly variations from 0 to 33.3%. Years that stand out are especially 1990 to 1992, 1995, as well as 2016. The majority of all cases generally occurred between April and July, indicating also a seasonality of cases. This study evaluates the occurrence of fatal pharyngeal entrapment of fish in two geographically separated harbour porpoise populations. Additionally, common sole is clearly identified as a potentially risky item of prey for these small odontocetes.

A high-quality genetic reference database for European commercial fishes reveals substitution fraud of processed Atlantic cod (Gadus morhua) and common sole (Solea solea) at different steps in the Belgian supply chain.

Seafood is an important component of the human diet. With depleting fish stocks and increasing prices, seafood is prone to fraudulent substitution. DNA barcoding has illustrated fraudulent substitution of fishes in retail and restaurants. Whether substitution also occurs in other steps of the supply chain remains largely unknown. DNA barcoding relies on public reference databases for species identification, but these can contain incorrect identifications. The creation of a high quality genetic reference database for 42 European commercially important fishes was initiated containing 145 Cytochrome c oxidase subunit I (COI) and 152 Cytochrome b (cytB) sequences. This database was used to identify substitution rates of Atlantic cod (Gadus morhua) and common sole (Solea solea) along the fish supply chain in Belgium using DNA barcoding. Three out of 132 cod samples were substituted, in catering (6%), import (5%) and fishmongers (3%). Seven out of the 41 processed sole samples were substituted, in wholesale (100%), food services (50%), retailers (20%) and catering (8%). Results show that substitution of G. morhua and S. solea is not restricted to restaurants, but occurs in other parts of the supply chain, warranting for more stringent controls along the supply chain to increase transparency and trust among consumers.

Metazoan Parasites of Common Sole (Solea Solea) and Scaldfish (Arnoglossus Laterna) (Pleuronectiformes) from Sinop Coast of Black Sea.

The metazoan parasites were investigated of two flatfish the common sole, Solea solea (n:140) and the scaldfish, Arnoglossus laterna (n: 22) in the Sinop coast of Black Sea from June 2015 to June 2017. A total of 15 metazoan parasite species belonging to Digenea (6), Cestoda (3), Acanthocephala (1), Nematoda (4) and Isopoda (1) taxonomic groups were identified. Solea solea was found to be infected by Condylocotyla pilodora, Proctoeces maculatus, Opecoelidae gen. sp., Metadena sp., Stephanostomum sp., Progrillotia sp., Capillaria gracilis, Cucullanus campanae, Solearhynchus rhytidotes and Nerocila orbignyi. Arnoglossus laterna was found to be infected by Lecithochirium musculus and Grillotia erinaceus. Scolex pleuronectis, Hysterothylacium aduncum and Dichelyne minutus were determined in both flatfish. Infection prevalence and mean intensity values were recorded for each parasite species. Infection values for each parasite species in relation to season and fish size were also determined and compared as comparatively. This study is the first one assessing the metazoan parasites both of S. solea and A. laterna collected from the Turkish coast of Black Sea. While Condylocotyle pilodora and Capillaria gracilis are new parasite records for S. solea, Grillotia erinecaus is new parasite record for A. laterna. Moreover, this paper is the first report on occurrence of Opecoelidae gen. sp., Metadena and Stephanostomum genera in S. solea.

Complex effect of projected sea temperature and wind change on flatfish dispersal.

Climate change not only alters ocean physics and chemistry but also affects the biota. Larval dispersal patterns from spawning to nursery grounds and larval survival are driven by hydrodynamic processes and shaped by (a)biotic environmental factors. Therefore, it is important to understand the impacts of increased temperature rise and changes in wind speed and direction on larval drift and survival. We apply a particle-tracking model coupled to a 3D-hydrodynamic model of the English Channel and the North Sea to study the dispersal dynamics of the exploited flatfish (common) sole (Solea solea). We first assess model robustness and interannual variability in larval transport over the period 1995-2011. Then, using a subset of representative years (2003-2011), we investigate the impact of climate change on larval dispersal, connectivity patterns and recruitment at the nursery grounds. The impacts of five scenarios inspired by the 2040 projections of the Intergovernmental Panel on Climate Change are discussed and compared with interannual variability. The results suggest that 33% of the year-to-year recruitment variability is explained at a regional scale and that a 9-year period is sufficient to capture interannual variability in dispersal dynamics. In the scenario involving a temperature increase, early spawning and a wind change, the model predicts that (i) dispersal distance (+70%) and pelagic larval duration (+22%) will increase in response to the reduced temperature (-9%) experienced by early hatched larvae, (ii) larval recruitment at the nursery grounds will increase in some areas (36%) and decrease in others (-58%) and (iii) connectivity will show contrasting changes between areas. At the regional scale, our model predicts considerable changes in larval recruitment (+9%) and connectivity (retention -4% and seeding +37%) due to global change. All of these factors affect the distribution and productivity of sole and therefore the functioning of the demersal ecosystem and fisheries management.

Ultrastructural morphology of the envelope of Dover sole Solea solea eggs from fertilization until hatching with emphasis on sample preparation.

This study is the first to describe the ultrastructural morphology of the envelope of Solea solea eggs from fertilisation until hatching. Defining the ultrastructural morphology of fish eggs is important for species identification and may assist in predicting the effect of external influences on these early life stages. In first instance, various fixation and embedding protocols were assessed to explore the morphology of the egg envelope, whereby the encountered difficulties were highlighted. The successful protocol for SEM proved to be combined fixation with 4% glutaraldehyde in 0.1M cacodylate buffer for minimum 4h with post-fixation of 2h with 1% OsO4 in 0.1M cacodylate buffer. For TEM, puncturing the egg envelope during the first steps of the fixation protocol was necessary to allow the embedding medium to penetrate through the egg envelope. Based on both scanning and transmission electron microscopical examination, three distinct layers were discerned in the egg envelope. During the development of the fish embryo, a change in the outer structure of the egg was observed. Scanning electron microscopical examination of one day post-fertilisation eggs (DPF) revealed a homogeneous outer layer, displaying a large number of pores uniformly distributed on the surface of the egg envelope. Starting from 2 DPF parts of the outermost layer or two outer layers peeled off. The second deeper layer showed larger pores, with less defined edges. In the third innermost layer irregular indentations were noted. On transmission electron microscopy the first outermost layer of 1 DPF eggs clearly folded into the pores. The second layer was more electron dense, had a uniform appearance and did not cover the surface of the pores. The third innermost layer was much thicker and possessed indentations. A total number of 12 undulating zones were discriminated based on different degrees of electron density. Prior to hatching, the compact structure of the innermost layer was distorted by dispersed holes and tears.

In- and outdoor reproduction of first generation common sole Solea solea under a natural photothermal regime: Temporal progression of sexual maturation assessed by monitoring plasma steroids and gonadotropin mRNA expression.

Reproduction of many temperate fishes is seasonal and maturation and spawning of gametes are under photothermal control. Reproductive success of first generation (G1) common sole Solea solea in captivity has been low. In this study, the sexual maturation status has been assessed during the prespawning months in G1 sole that were housed (a) outdoor under the natural photoperiod and temperature, or (b) indoor under artificial photothermal induction. Maturation was assessed in male and female G1 broodstock in November as controls, after which the remaining population was divided over two outdoor flow-through tanks placed in a pond and two indoor recirculating aquaculture system (RAS) tanks. Subsequently, maturation status (gonadosomatic index GSI and plasma levels of testosterone T and 17ß-estradiol E2) was assessed in one tank for each condition in January, February and during spawning in early April, while fish in the other tank were not disturbed in achieving reproductive success. Quantitative real-time PCR was performed to determine species-specific gonadotropin mRNA expression in females. Successful G1 spawning and egg fertilisation occurred in all experimental tanks. Gonadal development was similar under both conditions. Higher E2 and T levels were found in indoor housed females. Gonadotropin expression revealed similar profiles between outdoor and indoor housed females. G1 sole could be reproduced in the outdoor tanks under the natural photoperiod and in the indoor tanks under artificial simulation of this regime that includes a potentially crucial chilling period of 2-3 months at 5-7 °C.