Pseudorasbora parva - Stone moroko

The Stone moroko is originally native to East Asia, specifically in Siberia, Korea, China, and Japan ^[2].

First observation in Belgium

The first observations in Belgium date back to 1992 ^[3]. In the Lower Scheldt Basin, the earliest sightings were from 1998 ^[4].

Distribution in Belgium

The Stone moroko is generally found in Belgian river systems (i.e., fresh water) north of the Sambre and Meuse ^[5]. In the Lower Scheldt and the Scheldt estuary, the species has been encountered multiple times at various locations since 1998 ^[5,6]. Further south, the species is established in several larger and smaller rivers but is less widespread ^[7,8]. This is primarily due to the Stone moroko's preference for slow-flowing and stagnant waters, resulting in less suitable habitat in Wallonia. Additionally, the stocking of fish for angling (particularly carp species) in Flanders, which were often infected with Stone moroko, has significantly contributed to its introduction and spread. In Wallonia, however, stocking efforts mainly involved salmonids, which were much less likely to be infected with Stone moroko. 
 

Distribution in neighbouring countries

In 1992, the Stone moroko was first observed in the Dutch Meuse ^[9]. Ten years later, it had colonised the entire course of the Meuse and spread rapidly, making the Stone moroko now widely distributed along all major river systems ^[10]. It has since become the most widespread non-native fish species in the Atlantic bioregion, found in every river basin ^[3,8,10,11], with the Iberian Peninsula being one of the few European regions not yet colonised ^[12]. However, in 2012, this changed as a study showed that the Stone moroko had also established itself there, specifically in the Guadiana River basin ^[13].

This fish was introduced to Europe as a contaminant (including eggs) of the breeding and transport of other fish species, primarily Asian carps (aquaculture) ^[2,7]. The first introduction occurred in the 1960s, in Romania and Hungary, from where the species colonised the Danube River basin ^[2]. The introduction to the Atlantic bioregion dates back to the early 1990s and also occurred via the aforementioned introduction vectors ^[5]. A significant secondary vector is natural dispersal ^[14], but for Belgium, it is certain that the species was introduced via contaminated fish transports ^[3,4].

The Stone moroko is not very selective in its habitat choice. It can be found in both stagnant and flowing waters (ponds, lakes, pools, ditches, streams, rivers, and canals). The species reaches its highest density in shallow, densely vegetated, stagnant waters, often located in floodplains ^[2,7,16]. The success of this exotic species can be attributed to its lifestyle: omnivorous diet, rapid generation turnover, multiple broods per year, parental care, and high resistance to new pathogens and parasites ^[8,15-17]. Additionally, this species tolerates temperatures ranging from 5 to 22°C ^[18].

The species is tolerant of extreme conditions, such as low water levels, high water temperatures, low oxygen concentrations, water pollution, and algal blooms ^[9]. Reproduction occurs mainly in stagnant waters, such as ponds and pools with relatively high water temperatures ^[9,16].

Because the Stone moroko adapts easily and can reach very high local densities, it is one of the most successful invasive freshwater fish species ^[3,9]. Several countries have reported adverse ecological impacts following the introduction of this fish ^[14]. The species causes negative effects on some native fish species through predation on eggs and larvae, competition for food, and the transmission of the harmful single-celled parasite Sphaerothecum destruens ^[9,19]. The Stone moroko itself is not affected by this parasite, but the pathogen increases mortality rates and decreases reproductive success among several native species ^[2]. In fish farms, this fish is considered a highly undesirable species due to its competition for food with other carp species ^[9].

Since August 2016, the Stone moroko has been listed on the EU list of invasive species. This means that there is a European ban on possession, trade, breeding, transport, and import of this species. Furthermore, member states are required to locate and remove populations present in the wild, or, if the species is already widespread, to manage it in a way that minimises further spread and damage. However, a 2010 study showed that the detection time (i.e., the time between introduction and first observation) for this species averages about four years, which is too long to prevent the further spread of such opportunistic species ^[14].

Control measures are known only for stagnant waters ^[8]. In northern England, an established population in a lake was successfully eradicated using a piscicide based on rotenone. Non-target species were captured before treatment and successfully reintroduced after the rotenone had degraded ^[20]. However, this treatment is difficult to apply in Belgium due to strict regulations on the use of biocides in aquatic environments ^[8]. No non-chemical treatment has proven effective for eradicating populations in rivers. The national (Belgium) eradication measures therefore only apply to stagnant water bodies and do not address river systems. These include a combination or separate application of drainage (with non-target species removed and quarantined beforehand) and/or biomanipulation (introducing specific native predatory fish) ^[8]. The latter technique has proven effective in some cases ^[21]. After eradication, follow-up should be carried out using eDNA technology ^[22] and/or capture methods (traps, electrofishing). The management strategy to limit further spread is mainly focused on preventing the spread of propagules ^[8].

The Stone moroko is primarily a freshwater fish but can also be found in brackish water environments ^[23], such as the floodplains of the Scheldt estuary or the Lower Scheldt ^[2,6,7]. It is a small carp-like fish, growing to about 8-10 cm in length (maximum 12.5 cm ^[17]), with a small, upward-facing mouth (the lower jaw extends beyond the upper jaw) and without barbels. The fish has a silver-gray color with a dark stripe running along the flank, although this stripe is not always visible. Its body is covered with distinctly visible black-edged scales. The fish has 35 to 38 scales along the lateral line ^[7]. Like all other carp species, the Stone moroko has one dorsal fin, two pectoral fins, and two pelvic fins that are not fused ^[24].

The Stone moroko lives for up to three years and becomes sexually mature after one year. Spawning occurs in the spring (March-June). During this period, a female can spawn three to four times. The male keeps the eggs clean and guards them until they hatch ^[16]. The eggs are deposited on aquatic plants, branches, or stones ^[9]. The species is omnivorous and feeds on a broad range of invertebrates and plant material ^[16,25].

[1]          World Register of Marine Species (WoRMS) (2024). Pseudorasbora parva (Temminck & Schlegel, 1846) https://www.marinespecies.org/aphia.php?p=taxdetails&id=465541 (2024-10-18). 

[2]          Nederlandse Voedsel- en Warenautoriteit (2019). Factsheet Blauwband (Pseudorasbora parva). Ministerie van Landbouw, Natuur en Voedselkwaliteit: De Hague. 4 pp. [https://www.vliz.be/en/imis?module=ref&refid=393992] 

[3]          Verreycken, H.; Anseeuw, D.; Van Thuyne, G.; Quataert, P.; Belpaire, C. (2007). The non-indigenous freshwater fishes of Flanders (Belgium): review, status and trends over the last decade. J. Fish Biol. 71(suppl. D): 160-172. [https://www.vliz.be/nl/imis?module=ref&refid=194615] 

[4]          Verreycken, H. (2024). Persoonlijke mededeling.

[5]          waarnemingen.be. Pseudorasbora parva (Temminck & Schlegel, 1846). https://waarnemingen.be/species/2196/ (2024-02-27)

[6]          Bauwens, F.; Van den Neucker, T. (2023). Een speurtocht naar niet-inheemse soorten in het Galgeschoor en het Doeldok te Antwerpen. De Strandvlo 43(2): 39-50. [https://www.vliz.be/nl/imis?module=ref&refid=380571] 

[7]          (2019). Invasieve uitheemse soorten van de unielijst: informatiegids voor België. Editie 2019. Nationaal Wetenschappelijk Secretariaat voor Invasieve Uitheemse Soorten/Koninklijk Belgisch Instituut voor Natuurwetenschappen: Brussels. 149 pp. [https://www.vliz.be/nl/imis?module=ref&refid=319775]  

[8]          Adriaens, T; Branquart, E.; Gosse, D.; Reniers, J.; Vanderhoeven, S. (2019). Feasibility of eradication and spread limitation for species of Union concern sensu the EU IAS Regulation (EU 1143/2014) in Belgium. Report prepared in support of implementing the IAS Regulation in Belgium. Institute for Nature and Forest Research/Service Public de Wallonie/National Scientific Secretariat on Invasive Alien Species/Belgian Biodiversity Platform: [s.l.]. 222 pp. [https://www.vliz.be/en/imis?module=ref&refid=393990] 

[9]          Spikmans, F. Blauwband Pseudorasbora parva. Nederlands Soortenregister – overzicht van de Nederlandse biodiversiteit. https://www.nederlandsesoorten.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=138736&cat=147 (2024-02-27)

[10]        GBIF. Pseudorasbora parva (Temminck & Schlegel, 1846). https://www.gbif.org/species/2362868 (2024-02-27)

[11]        Copp, G.H.; Garthwaite, R.; Gozlan, R.E. (2005). Risk identification and assessment of non-native freshwater fishes: a summary of concepts and perspectives on protocols for the UK. J. Appl. Ichthyol. 21(4): 371-373. [https://www.vliz.be/en/imis?module=ref&refid=393988] 

[12]        Caiola, N.; de Sostoa, A. (2002). First record of the Asiatic cyprinid Pseudorasbora parva in the Iberian Peninsula. J. Fish Biol. 61(4): 1058-1060. [https://www.vliz.be/en/imis?module=ref&refid=393987] 

[13]        Aparico, E.; Peris, B.; Torrijos, L.; Prenda, J.; Nieva, A.; Perea, S. (2012). Expansion of the invasive Pseudorasbora parva (Cyprinidae) in the Iberian Peninsula: first record in the Guadiana River basin. Cybium 36(4): 585-586. [https://www.vliz.be/en/imis?module=ref&refid=393986]  

[14]        Gozlan, Rodolphe E; Andreou, Demetra; Asaeda, Takashi; Beyer, Kathleen; Bouhadad, Rachid; Burnard, Dean; Caiola, Nuno; Cakic, Predrag; Djikanovic, Vesna; Esmaeili, Hamid R; Falka, Istvan; Golicher, Duncan; Harka, Akos; Jeney, Galina; Kováč, Vladimír; Musil, Jiří; Nocita, Annamaria; Povz, Meta; Poulet, Nicolas; Virbickas, Tomas; Wolter, Christian; Serhan Tarkan, A; Tricarico, Elena; Trichkova, Teodora; Verreycken, Hugo; Witkowski, Andrzej; Guang Zhang, Chun; Zweimueller, Irene; Robert Britton, J (2010). Pan-continental invasion of Pseudorasbora parva: towards a better understanding of freshwater fish invasions. Fish Fish. 11(4): 315-340. [https://www.vliz.be/en/imis?module=ref&refid=393985] 

[15]        Spikmans, F.; van Kessel, N.; Dorenbosch, M.; Kranenbarg, J.; Bosveld, J.; Leuven, R. (2010). Plaag Risico Analyses van tien exotische vissoorten in Nederland. Nederlands Centrum voor Natuuronderzoek/Stichting Bargerveen/Radboud Universiteit Nijmegen/Stichting RAVON/Natuurbalans - Limes Divergens: Nijmegen. 84 pp. [https://www.vliz.be/en/imis?module=ref&refid=393983] 

[16]        Kottelat, M.; Freyhof, J. (2007). Handbook of European freshwater fishes. Publications Kottelat: Cornol. ISBN 978-2-8399-0298-4. 646 pp. [https://www.vliz.be/en/imis?module=ref&refid=393982] 

[17]        Froese, R.;  Pauly, D. (Eds.). (2023). FishBase. World Wide Web electronic publication. www.fishbase.org. (10/2023)

[18]        Baensch, H.A.; Riehl, R. (1985). Aquarien atlas. Band 2. Mergus, Verlag für Natur-und Heimtierkunde GmbH: Melle. ISBN 3-88244-011-2. 1216 pp. [https://www.vliz.be/en/imis?module=ref&refid=393980] 

[19]        Spikmans, F.; van Tongeren, T.; van Alen, T.; van der Velde, G.; Op den Camp, H. (2013). High prevalence of the parasite Sphaerothecum destruens in the invasive topmouth gudgeon Pseudorasbora parva in the Netherlands, a potential threat to native freshwater fish. Aquat. Invasions 8(3): 355-360. [https://www.vliz.be/en/imis?module=ref&refid=393977] 

[20]        Britton, J.R.; Brazier, M. (2006). Eradicating the invasive topmouth gudgeon, Pseudorasbora parva, from a recreational fishery in northern England. Fish. Manage. Ecol. 13(5): 329-335. [https://www.vliz.be/en/imis?module=ref&refid=393976] 

[21]        Lemmens, P.; Mergeay, J.; Vanhove, T.; De Meester, L.; Declerck, S.A.J. (2015). Suppression of invasive topmouth gudgeon Pseudorasbora parva by native pike Esox lucius in ponds. Aquat. Conserv. 25(1): 41-48. [https://www.vliz.be/en/imis?module=ref&refid=393975] 

[22]        Davison, P.I.; Copp, G.H.; Creach, V.; Vilizzi, L.; Britton, J.R. (2017). Application of environmental DNA analysis to inform invasive fish eradication operations. Naturwissenschaften 104(3-4): 35. [https://www.vliz.be/en/imis?module=ref&refid=393970] 

[23]        Gavriloaie, C.; Burlacu, L.; Bucur, C.; Berkesy, C. (2014). Notes concerning the distribution of Asian fish species, Pseudorasbora parva, in Europe. AACL Bioflux 7(1): 43-50. [https://www.vliz.be/en/imis?module=ref&refid=393969]  

[24]        (S.d.). Project Invasieve Exoten – Herkenningsfiche. Blauwbandgrondel Pseudorasbora parva. Natuurpunt/INBO/Natagora/Leefmilieu Brussel/Agentschap Natuur en Bos (ANB): [s.l.]. 2 pp. [https://www.vliz.be/en/imis?module=ref&refid=393968] 

[25]        Billard, R. (1997). Les poissons d’eau douce des rivières de France: identification, inventaire et répartition des 83 espèces. Delachaux et Niestlé: Paris. ISBN 2603010468. 192 pp. [https://www.vliz.be/en/imis?module=ref&refid=393967]

VLIZ Alien Species Consortium (2024). Pseudorasbora parva – Stone moroko. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 6 pp.