Stone moroko (Pseudorasbora parva)

Common Names: Topmouth gudgeon

Description: Introduced into ponds in the 1960s throughout Europe. They are the carrier of a parasite (Sphaerothecum destruens) that can negatively impact native fish populations.

Identification: Elongate body, slightly flattened on sides, resembling the Gobio species. Up to 110 mm. , mouth in top position with short dorsal and anal fins. Caudal fin is large and deeply incised. Grey back, pale sides/belly. Characteristic lunate spots in caudal part of scales. Fins pale with a darker stripe running obliquely backwards on dorsal fin.

Habitat: Native to east Asia, western and southern parts of the Korean Peninsula and Taiwan. Prefers well vegetated small channels, ponds and small lakes. Adults occur in cool, shallow water, either still or slow-flowing.

Reproduction: Spawning takes place at 1 year of age, requiring water temps of 60-66 degrees F. Females produce a few hundred to a few thousand eggs. Spawning can take place 3-4 times per season. Eggs are laid on plants, sand, stones, and mollusk shells which the female cleans prior to egg-laying. Several dozen eggs are laid at once and the males guard the eggs until they hatch.

Impact and Damage: Competes for food with native and farmed fish species, plus competition for space and spawning habitat. It is a vector of infectious diseases such as Spherotecum destruens, Anguillicola crassus and Clinostomum complanatum as well as a carrier of Pike Fry Rhabdovirus (PFR). It also consumes large amounts of zooplankton which results in an increase in phytoplankton abundance, and subsequent increase in eutrophication.

Monitoring and rapid response: One population in England was eradicated using rotenone.

Credits: The information provided in this factsheet was gathered from the NNSS: GB Non-native Species Secretariat.

Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).

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