No abstract

The Baltic is a semi-enclosed sea characterised by decreasing salinity in the eastern and northern direction with only the deeper parts of the southern Baltic suitable as spawning grounds for marine species like cod. Baltic cod exhibits various adaptations to brackish water conditions, yet the inflow of salty North Sea water near the bottom remains an influence on the spawning success of the Baltic cod. The eastern Baltic population has been very weakly studied in comparison with the western population. The aim of this study is to demonstrate for the first time genetic differentiation by the use of a large number of SNPs between eastern and western Baltic populations existing in differentiated salinity conditions. Two cod samples were collected from the Bay of Gdańsk, Poland and one from the Kiel Bight, Germany. Samples were genotyped using a cod derived SNP-array (Illumina) with 10 913 SNPs. A selection of diagnostic SNPs was performed. A set of 7944 validated SNPs were analysed to assess the differentiation of three samples of cod. Results indicated a clear distinctness of the Kiel Bight from the populations of the eastern Baltic. FST comparison between both eastern samples was non-significant. Clustering analysis, principal coordinates analysis and assignment test clearly indicated that the eastern samples should be considered as one subpopulation, well differentiated from the western subpopulation. With the SNP approach, no differentiation between groups containing 'healthy' and 'non-healthy' cod individuals was observed.

Anisakids of Scomber japonicus, Trachyrincus scabrus, Sardina pilchardus, Merluccius polli, Trachurus trachurus, and Hoplostethus cadenati from African shelf are reported. Parasites were extensively studied with respect to their morphology and sequence analysis of the rDNA fragment (containing internal transcribed spacer [ITS]-1, 5.8S subunit and ITS-2); all of them are approximately 1,000 base pairs. Digestion of the amplified region and its sequencing revealed the presence of a sibling species (A. simplex s.s. and A. pegreffii). Still other sequences represented closely related, but not sibling, species, i.e., Anisakis brevispiculata, A. ziphidarum, and A. physeteris; there were also 2 undescribed anisakid species. These species were temporarily described as Anisakis sp. HC-2005 and Anisakis sp. MP-2005 (found, respectively, in Hoplostethus cadenati and Merluccius polli). The study shows that the parasitic fauna of fishes reflects not only the geographic range of anisakid nematodes but also the feeding behavior of the hosts serving as links in the parasites' life cycles.

Kijewska, A., Burzyński, A., and Wenne, R. 2009. Molecular identification of European flounder (Platichthys flesus) and its hybrids with European plaice (Pleuronectes platessa). – ICES Journal of Marine Science, 66: 902–906. European flounder (Platichthys flesus) and plaice (Pleuronectes platessa) are commercially important marine fish species inhabiting the continental shelf waters of Europe. Morphological similarity between the two makes it difficult to identify their hybrids, so species misclassification can generate errors in defining stocks in terms of their conservation and management. Flounder and plaice populations from the North Sea and the Baltic Sea were studied. Mitochondrial DNA (mtDNA) was used to confirm the morphological species identification. The set of molecular markers, two mitochondrial (cytochrome b and D-loop) and two nuclear (the ribosomal marker ITS and parathyroid hormone-related protein gene), was constructed to identify the two flatfish species and their hybrids. “Pure” flounder (P. flesus) were observed in the Bay of Gdańsk, Baltic Sea, and off the coast of Denmark in the North Sea. The fishing area near Bornholm in the Baltic is rich in P. flesus × P. platessa hybrids. The length difference of the amplified D-loop fragment was used for species identification. The characteristics of heteroplasmy in the control region (D-loop) can be useful as a population marker in the European flounder. Our studies demonstrate the utility of mtDNA polymorphism combined with nuclear molecular markers for correct identification of the morphologically similar and hybridized European flounder and plaice.