A specimen of the invasive Callinectes sapidus was recently found in the catchment basin of the Baltic Sea (Lake Dąbie, Poland). The discovery is significant because it indicates a widening of the crab's biogeographic range in northern Europe and confirms its expansion along European estuaries. The captured juvenile specimen from Lake Dąbie (estuary of the Oder River) had a carapace width (CW) of 125.58 mm, carapace length (CL) of 53.23 mm, and weight (w) of 100.19 g. This is the first record of this species in this part of the Baltic Sea catchment basin, following the discovery of a female caught in a plaice net northeast of Copenhagen (1951) and an adult male caught off Skagen, Northern Jutland, between the Kattegat and the Skagerrak (2007).
For the last few decades there have been reports not only of the occurrence of new invasive species of European watercourses, but also their increasing expansion. One of such species is the Amur sleeper (Perccottus glenii). The present work contains assessment of age and length distribution, condition as well as growth rate and analysis of the parasite fauna of the Amur sleeper from the waters of the Vistula River tributary in its middle course (the Habdziński Canal). During the catch performed in 2017 and 2019, the total of 177 Amur sleepers were recorded in the studied watercourse and a statistically significant sex structure disproportion was observed. Among the specimens caught in 2017 dominant were fishes with lengths of 50.1–60.1 mm whereas in 2019 the majority of the Amur sleeper specimens measured 30.1–50.0 mm. Six age groups were recorded among the caught fish with a clear prevalence of specimens aged 1+ (70.06%). The most frequently recorded parasite of P. glenii was non-quantifiable Trichodina rostrata ciliate for which the Amur sleeper from the Polish waters appeared to be a new host. Moreover, the presence of an acanthocephalan Acanthocephalus lucii, not recorded in Poland in this host before, was observed in the chyme. Also, accidental presence of larvae of the Opisthioglyphe ranae tremadote, which is a parasite typical of amphibians, was also recorded. Despite unfavourable habitat conditions and increased volumes of biogenic substances in the waters of the Habdziński Canal, the Amur sleeper found convenient conditions to reside in this small watercourse.
Monitoring studies of ichthyofauna, in particular non-indigenous species, are an important element of research on aquatic ecosystems. This information is essential for modelling population growth and predicting rates of expansion, quantifying ecological impacts and assessing the efficacy of removal and control strategies. Actually, the most compelling fish invasion in Polish freshwaters is arguably the accidental introduction of the topmouth gudgeon (Pseudorasbora parva). Age and lengths structure, condition factor and growth rate of the invasive populations of the topmouth gudgeon from small Polish rivers was examined. The samples were collected from the rivers: Molnica (n = 41), Myśla (n = 21) and Wardynka (n = 101) soon after the invasion was recorded (2017). Estimated ages of topmouth gudgeon ranged from 1+ to 3+ for the Myśla River, from 1+ do 4+ for the Molnica River, and from 1+ to 5+ for the Wardynka River. The fish from the Molnica River was characterised by the lowest total and standard length (TL, SL), weight, and highest condition. The results of back-calculations and the parameters of von Bertalanffy’s growth equation revealed distinct disproportions in the standard length (mm) in individual age groups (Molnica River: Lt = 54.94 [1 – e–0.68885 (1 – 0.003404)], Myśla River: Lt = 55.39 [1 – e–0.74921 (1 – 0.030962)], Wardynka River: Lt = 66.33 [1 – e–0.69348 (1 – 0.369505)]). The introduction of the topmouth gudgeon occurred in the upper and medium sectors of small rivers, but in subsequent years the species migrated to new sites further downstream and this may have affected the native ichthyofauna.
PL
Badania monitoringowe ichtiofauny, w szczególności gatunków nierodzimych, są ważnym elementem badań nad ekosystemami wodnymi. Informacje te są niezbędne do modelowania wzrostu populacji i przewidywania tempa ekspansji, ilościowego określania skutków ekologicznych i oceny skuteczności strategii eliminacji tych ryb z wód rodzimych oraz ich kontroli. Jednym z najbardziej interesujących gatunków inwazyjnych w świecie ryb w polskich słodkowodnych wodach jest prawdopodobnie przypadkowe wprowadzenie czebaczka amurskiego (Pseudorasbora parva). W pracy analizowano strukturę wieku i długości, współczynnik kondycji i tempo wzrostu inwazyjnych populacji czebaczków amurskich z małych cieków w Polsce. Ryby złowiono w 2017 r. z rzek: Molnica (n = 41), Myśla (n = 21) i Wardynka (n = 101). Szacowany wiek czebaczków amurskich wynosił od 1+ do 3+ (Myśla), od 1+ do 4+ (Molnica) i od 1+ do 5+ (Wardynka). Ryby z Molnicy cechowały się najmniejszą długością całkowitą i długością ciała (TL, SL) oraz masą osobniczą. Odczyty wsteczne i parametry równania wzrostu von Bertalanffy’ego ujawniły wyraźne dysproporcje w długości całkowitej w poszczególnych grupach wiekowych (rzeka Molnica: Lt = 54,94 [1 – e–0,68885 (1 – 0,003404)], rzeka Myśla: Lt = 55,39 [1 – e–0,74921 (1 – 0,030962)], rzeka Wardynka: Lt = 66,33 [1 – e–0,69348 (1 – 0,369505)]). Wprowadzenie czebaczka amurskiego miało miejsce w górnej i środkowej strefie małych cieków, ale w kolejnych latach gatunek ten może migrować do nowych miejsc zlokalizowanych w dolnych odcinkach rzek i może wpływać na rodzimą ichtiofaunę.
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