Large-scale sequencing of flatfish genomes provides insights into the polyphyletic origin of their specialized body plan

The evolutionary and genetic origins of the specialized body plan of flatfish are largely unclear. We analyzed the genomes of 11 flatfish species representing 9 of the 14 Pleuronectiforme families and conclude that Pleuronectoidei and Psettodoidei do not form a monophyletic group, suggesting independent origins from different percoid ancestors. Genomic and transcriptomic data indicate that genes related to WNT and retinoic acid pathways, hampered musculature and reduced lipids might have functioned in the evolution of the specialized body plan of Pleuronectoidei. Evolution of Psettodoidei involved similar but not identical genes. Our work provides valuable resources and insights for understanding the genetic origins of the unusual body plan of flatfishes.

The proportion of flatfish recruitment in the North Sea potentially affected by offshore windfarms

Understanding the influence of man-made infrastructures on fish population dynamics is an important issue for fisheries management. This is particularly the case because of the steady proliferation of offshore wind farms (OWFs). Several flatfish species are likely to be affected because areas with OWFs in place or planned for show a spatial overlap with their spawning grounds. This study focuses on six commercially important flatfish species in the North Sea: common sole (Solea solea), European plaice (Pleuronectes platessa), turbot (Scophthalmus maximus), brill (Scophtalmus rhombus), European flounder (Platichthys flesus), and common dab (Limanda limanda). We used a particle-tracking model (Larvae&Co) coupled to a 3D hydrodynamic model to assess the effects of spatial overlap of OWFs with the species’ spawning grounds on the larval fluxes to known nursery grounds. An important overlap between planned areas of OWFs and flatfish spawning grounds was detected, with a resulting proportion of settlers originating from those areas varying from 2% to 16%. Our study suggests that European plaice, common dab, and brill could be the most affected flatfish species, yet with some important local disparities across the North Sea. Consequently, the study represents a first step to quantify the potential impact of OWFs on flatfish settlement, and hence on their population dynamics.

External morphology, postcranial and appendicular osteology of three southwestern Atlantic flatfishes ( Paralichthys , Paralichthyidae), and comparisons with other congeneric species

ABSTRACT Comparisons of the external morphology and analysis of osteological features of the postcranial and appendicular skeletons of three southwestern Atlantic flatfish species of the genus Paralichthys (P. isosceles, P. orbignyanus and P. patagonicus) were carried out. Bones are described, and detailed morphological, morphometric and meristic characteristics of these flounders are given in order to provide information about the external and internal morphology of three species of Paralichthys occurring in the south-west Atlantic waters that add new information and will help regarding within the framework of a phylogenetic study of the group. Interspecific differences were found in the number of vertebrae and intermuscular bones, as well as in the morphology and morphometry of vertebrae, caudal skeletons, pectoral and pelvic girdle bones. Relationships between bones are discussed and bone characteristics compared with those found in other species of Paralichthys and in other pleuronectiform species. The position of Paralichthys isosceles within Paralichthys is discussed, along with other congeners such as P. triocellatus and P. oblongus.

FLEXSELECT: counter-herding device to reduce bycatch in crustacean trawl fisheries

FLEXSELECT is a simple counter-herding device that aims at reducing the bycatch of fish by scaring them away from the trawl path without affecting the catches of the target species. FLEXSELECT was tested in the Norway lobster (Nephrops norvegicus) directed trawl fishery, as this includes bycatch of both roundfish and flatfish. Length-based data were collected for Nephrops, four roundfish species (cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and hake (Merluccius merluccius)), and two flatfish species (plaice (Pleuronectes platessa) and lemon sole (Microstomus kitt)), and length-based catch comparisons were performed. No significant effect on the target species, Nephrops, was detected, whereas a reduction of 39% (CI: 29%–46%) was obtained for the overall number of fish. Catches of all the six fish species examined were significantly reduced by FLEXSELECT, with the efficiency varying considerably among species and over length classes. No significant diel differences were found for either roundfish or flatfish species. FLEXSELECT prevents bycatch species from interacting with the trawl, thus most likely enhancing their survival and fitness. Moreover, its fast attachment system makes FLEXSELECT a flexible tool, adaptable to different fisheries and catch goals.