Reaching the steady state: 30 years of Anguillicola crassus infection of European eel, Anguilla anguilla L., in Northern Germany.

A 30 years long data series on the infection dynamics of European eel (Anguilla anguilla L.) with the non-native invasive nematode Anguillicola crassus Kuwahara, Niimi & Hagaki, 1974 is presented. Parasite burden was evaluated for 30 years in inland and coastal waters in Mecklenburg-Western Pomerania from 1991 to 2020. The total prevalence, mean intensity and damage status of the swim bladders were very high during the first decade (1991­2000), and significantly decreased in both marine and freshwater eel populations in the following decades (2001­2010, 2011­2020). The parasite intensity of eels in coastal waters was significantly lower compared with the freshwater systems (61.3% vs 79.5% in the first decade), indicating the vulnerability of the parasites to brackish water conditions and the fact that the life cycle of A. crassus cannot be completed under high saline conditions. Eel caught in the western part of the Baltic Sea (west of Darss sill) had the lowest mean infection (51.8% in first decade) compared to the eastern part with 63.8%. Thus, besides different infection patterns caused by the environmental conditions, a temporal trend towards a reduced parasite intensity and a more balanced parasite­host relationship developed in the 30 years of interaction after the first invasion. Possible reasons and mechanisms for the observed trends in parasite­host interactions are discussed.

Parasitation of sea trout (Salmo trutta trutta L.) from the spawning ground and German coastal waters off Mecklenburg-Western Pomerania, Baltic Sea.

A total of 52 sea trouts, Salmo trutta trutta, were studied for parasites, originating from German freshwater streams and coastal waters of the Baltic Sea. While 35 specimens were caught mainly close to the shoreline in the Baltic Sea, 17 were sampled during their spawning migration in Warnow River and other neighboring rivers in Mecklenburg-Western Pomerania. A total of 12 different metazoan parasite species were found in sea trout originating from the Baltic Sea, including five digeneans, two cestodes, three nematodes, and two acanthocephalans. Marine and freshwater species were found. In the migratory trout, seven different parasite species were recorded (one digenean, two cestodes, one nematode, and one acanthocephalan), demonstrating lower parasite diversity and load during the spawning migration compared with the fish from the Baltic Sea. The anisakid nematodes Anisakis simplex (sensu stricto), Contraceacum rudolphii, and Hysterothylacium aduncum were identified by molecular analyses of the ITS-1, 5.8S, ITS-2, and flanking sequences of the rDNA. Together with the digenean Derogenes varicus, Hemiurus communis and H. luehei, and the cestode Diphyllobothrium dendriticum seven new host records for sea trout from the German part of the Baltic Sea are made.

Fish Parasite Community of Three Lakes with Different Trophic Status in Mecklenburg-Western Pomerania, Germany.

PURPOSE: The present study investigates the fish parasite fauna from Lake Tollense, Mecklenburg-Western Pomerania, Germany. METHODS: A total of 117 perch (Perca fluviatilis), bream (Abramis brama) and roach (Rutilus rutilus) were sampled for parasites during 2018 and 2019 from Lake Tollense and compared with earlier data from Lake Malchin and Lake Hohen Sprenz in 2011 and 2014, respectively. Parasites were identified based on morphological and molecular characters. RESULTS: A total of 32 parasite species were isolated from fishes of Lake Tollense, predominated by digeneans. Diplostomum baeri was found only in perch while D. spathacaeum was isolated from bream and roach. Parasite comparison of similar hosts between lakes revealed highly abundant Ichthyocotylurus spp. in perch and bream of Lake Malchin while Aspidogaster limacoides was most common in roach from Lake Tollense. Diversity indices of roach showed significant variation between localities. However, NMDS graph revealed separation of the three freshwater habitats based on the parasite fauna of perch, bream and roach. CONCLUSION: Based on the multivariate statistical analysis, the three natural inland water bodies could be distinguished based on the parasite communities of perch, bream and roach. The potential to utilise fish parasites as biological indicators in freshwater ecosystem is discussed.

Allopodocotyle palmi sp. nov. and Prosorhynchus maternus Bray & Justine, 2006 (Digenea: Opecoelidae & Bucephalidae) from the Orange-Spotted Grouper Epinephelus coioides (Hamilton, 1822) off Bali, Indonesia, Described Using Modern Techniques.

BACKGROUND: The most convincing species of Allopodocotyle Pritchard, 1966 (Digenea: Opecoelidae) are known overwhelmingly from groupers (Serranidae: Epinephelinae). Six species of Allopodocotyle have been reported, collectively, from species of Cromileptes Swainson, 1839, Epinephelus Bloch, 1793 and Plectropomus Oken, 1817. These are A. epinepheli (Yamaguti, 1942), A. heronensis Downie & Cribb, 2011, A. manteri (Saoud & Ramadan, 1984), A. mecopera (Manter, 1940), A. plectropomi (Manter, 1963) and A. serrani (Yamaguti, 1952). In addition, a not yet fully described and unnamed seventh species, morphologically and phylogenetically close to A. epinepheli, was isolated from the orange-spotted grouper Epinephelus coioides (Hamilton, 1822) off Bali, Indonesia in 2016. An eighth species, again from E. coioides off Bali is described herein. METHODS: Morphological and phylogenetic analyses justify the recognition of A. palmi sp. nov., which is also genetically different from the as yet unnamed congener from the same host and locality. For the first time, 3D confocal laser scanning microscopy was applied to study and distinguish Digenea taxonomically. We introduce the 'Palm pattern', a new simplified way to visualise morphometric differences of related digenean taxa. RESULTS: Allopodocotyle palmi sp. nov. is distinguished from its congeners that infect groupers by its elongate body with a size > 2.7 mm and diagonal testes. The ovary is located mainly, and the anterior testis completely, in the posterior half of the body; the uterine coils are in the fourth eighth of the body. The cirrus-sac is 0.75-1.4 (1.1) mm long, its posterior extremity is well separated from the anterior extent of the vitelline fields, just reaching the anterior border of uterine coils. In addition, Prosorhynchus maternus Bray & Justine, 2006 (Bucephalidae) was isolated from E. coioides, representing the first record in Indonesia and the third record for this fish species. CONCLUSION: The biodiversity research in Indonesia is enhanced with a new species description based on modern and newly applied techniques.

Parasites of pufferfish, Lagocephalus spp. and Torquigener flavimaculosus of the Israeli Mediterranean: A new case of Lessepsian endoparasites.

With the opening of the Suez Canal as a link between the Red Sea and the Mediterranean Sea in 1869, the biogeographical event of the Lessepsian migration has been starting. Aided by beneficial conditions in the new habitat, almost 500 marine species have immigrated and often established themselves in the Mediterranean Sea, including several pufferfish species, with all of them extending their range and becoming important components of the local fauna. The parasitic fauna of these pufferfish has scarcely been examined in the Mediterranean Sea or in their native range, which provides the opportunity to study host-parasite interaction in a new habitat. The present study describes the parasitic fauna in four alien invasive pufferfish species (Lagocephalus guentheri, L. sceleratus, L. suezensis, and Torquigener flavimaculosus) of various sizes and ages on the Israeli Mediterranean coast. The parasite fauna of these species was diverse (Maculifer dayawanensis Digenea; Calliterarhynchus gracilis, Nybelinia africana and Tetraphyllidea larvae Cestoda; Hysterothylacium reliquens, Hysterothylacium sp. and Raphidascaris sp. Nematoda; Trachellobdella lubrica Hirudinea and Caligus fugu and Taeniacanthus lagocephali Copepoda) and consisted of mostly generalist species, most likely acquired in the new habitat, and specialist copepod ectoparasites, having co-invaded with the pufferfish. Additionally, the oioxenic opecoelid digenean Maculifer dayawanensis was found in two pufferfish species. The genus was previously only known from the Indo-Pacific Ocean, representing the eighth reported case of a Lessepsian endoparasite so far. Our results suggest a change in parasite fauna to native Mediterranean species in the pufferfish like previously reported in other Lessepsian migrant predatory fish species and a wider spread of co-invasion of fish endoparasites to the Mediterranean Sea than previously assumed. The study also provides several new host records and the first report for parasites in T. flavimaculosus.

Nematode Parasites in Baltic Sea Mammals, Grey Seal (Halichoerus grypus (Fabricius, 1791)) and Harbour Porpoise (Phocoena phocoena (L.)), from the German Coast.

PURPOSE: Endoparasitic nematodes of six harbour porpoises Phocoena phocoena and four grey seals Halichoerus grypus, stranded at the eastern coast of the Baltic Sea in Germany in winter 2019, were analysed in order to identify nematode parasites and to compare with recent studies from the same area. METHODS: Endoparasitic nematodes were identified by using both morphological and molecular characters. The successfully obtained sequences of the rDNA marker regions ITS-1, 5.8S, ITS-2 from 29 anisakid and the rDNA marker region ITS-2 of 11 pseudalid nematodes were amplified. RESULTS: Analyses revealed the presence of three parasite species, the anisakid nematode Contracaecum osculatum from grey seals and the pseudalid nematodes Pseudalius inflexus and Stenurus minor from the harbour porpoises. Other anisakid nematodes regularly occurring in the Baltic Sea, e.g. Anisakis simplex or Pseudoterranova decipiens, were not found. CONCLUSIONS: The prevalence of 100% and a severe parasite load in grey seals demonstrated a very high C. osculatum infection of Baltic Sea fish as their regular prey. Prevalence of 33% for parasites in harbour porpoises and minor infection rates, combined with a distinct lack of anisakid nematodes, are typical for the current situation of the porpoise parasite fauna in the Baltic Sea. Invasive parasite species as possible indicators for climate change could not be detected.

Metazoan parasite fauna of migrating common garfish, Belone belone (L.), in the Baltic Sea.

A total of 35 common garfish, Belone belone (Linnaeus, 1761), were studied for metazoan parasites on their spawning grounds in the western Baltic Sea. Nine parasite species were found, and six new locality records could be established for German coastal waters (Axine belones, Monogenea; Proteocephalus sp., Cestoda; Anisakis simplex (s.s.), Contracaecum rudolphii A and Hysterothylacium aduncum, Nematoda; Echinorhynchus gadi, Acanthocephala). For the first time, the marine ectoparasite A. belones was recorded from the gills of garfish inside the Baltic Sea, indicating its ability to survive the spawning migration as well as the brackish water conditions at its reproduction grounds. This is alike the endohelminth A. simplex (s.s.), that was identified by molecular analyses of the internal transcribed spacer (ITS-1, 5.8S, ITS-2) region. Almost all isolated metazoans were parasites commonly recorded from the northeast Atlantic Ocean and the North Sea. The lower number of typical generalist Baltic Sea parasites indicates the rapid migration of common garfish onto the spawning grounds, reducing the access and uptake of these species.

Metazoan parasites from herring (Clupea harengus L.) as biological indicators in the Baltic Sea.

Zoographical distribution of metazoan fish parasites in herring, Clupea harengus, from the Baltic Sea was analysed in order to use them as potential biological indicators. A total of 210 herring from six different sampling sites were investigated, harbouring 12 different parasite species [five digeneans (D), one cestode (C), three nematodes (N) and three acanthocephalans (A)]. The distribution of the parasite species differed according to region, with a distinct gradient of decreasing species richness towards the east of the Baltic Sea. The western localities at Kiel Bay, Rügen and Poland had the highest parasite diversity, including the marine parasite species Anisakis simplex (s.s.) (N), Brachyphallus crenatus and Hemiurus luehei (both D). The eastern localities had low parasite species richness, predominated by the freshwater digenean Diplostomum spathaceum. We could identify three different Baltic herring stocks, the spring-spawning herring of the western Baltic reaching from the Kattegat to the German and Polish coast, the stock of the central Baltic proper and the northern stock of C. harengus var. membras of the Gulf of Finland. The limited distribution of the herring parasites within the Baltic Sea enables their use as biological indicators for migration patterns and stock separation. The acanthocephalan Pomphorhynchus laevis that has already been used as an accumulation bioindicator for heavy metals was only recorded for the western herring stocks. However, the presence of mainly generalistic parasites and their uneven distribution patterns make their use as indicators for regional environmental and global change more difficult.