Topmouth gudgeon (Pseudorasbora parva)

Topmouth gudgeon
IUCN Red List species status – Least Concern LEAST

Top facts

  • The topmouth gudgeon is a small freshwater fish which has been widely introduced outside of its native East Asian range.
  • The topmouth gudgeon has been described as Europe’s most invasive fish species.
  • The female topmouth gudgeon can lay several batches of eggs each year, sticking them to a variety of surfaces.
  • The male topmouth gudgeon guards the eggs until they hatch.
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Topmouth gudgeon fact file

Topmouth gudgeon description

GenusPseudorasbora (1)

The topmouth gudgeon (Pseudorasbora parva) is a small East Asian fish which has been widely introduced outside of its native range and which has been described as Europe’s most invasive fish species (5) (6).

This freshwater fish has an elongated body, slightly flattened sides and an upturned mouth (2) (3) (4) (7). The dorsal and anal fins of the topmouth gudgeon are relatively short, but its tail fin is large and is deeply forked (2) (4). Although it may potentially grow to 11 centimetres in length, this species usually only reaches lengths of 8 to 9 centimetres (3) (4).

The topmouth gudgeon has a largely grey back, with paler sides and a paler belly which pass from yellowish-green through to silver (2) (3) (4). Each scale of this species is dark on the rear edge (2) (4) (7). The topmouth gudgeon’s fins are pale, and the dorsal fin is marked with a darker stripe (2) (4). Juveniles can be distinguished from adults by a dark stripe along the side of the body (2) (4) (7).

The male and female topmouth gudgeon differ in appearance during the breeding season, with the male becoming darker, particularly on the fins, while the female becomes paler. The male also develops tubercles on the head (2) (4) (7) (8). The male topmouth gudgeon is generally larger than the female (7) (9).

The topmouth gudgeon is reported to vary considerably in its external morphology across its range, and several subspecies have been described (8).

Also known as
clicker barb, false harlequin, false rasbora, false razbora, stone moroco, stone moroko, topmouth minnow.
Fundulus virescens, Leuciscus parvus, Leuciscus pusillus, Micraspius mianowskii, Pseudorasbora altipinna, Pseudorasbora depressirostris, Pseudorasbora fowleri, Pseudorasbora monstrosa.
Length: up to 11 cm (2) (3) (4)
17 - 19 g (3) (4)

Topmouth gudgeon biology

The topmouth gudgeon’s diet is quite varied, but usually consists of small insects, crustaceans and other aquatic invertebrates, as well as occasional fish eggs and larvae and some plant material (1) (7) (8) (10). This species sometimes takes food from the water’s surface, where its feeding activity is accompanied by an audible clicking sound that gives the topmouth gudgeon its alternative name of ‘clicker barb’ (7).

In its native range, the topmouth gudgeon typically breeds between May and August, but it may start breeding slightly earlier in parts of Europe (2) (3) (4). During the breeding season, male topmouth gudgeons establish territories which are aggressively defended. Larger males are likely to be more successful at defending a territory and attracting females (7).

In most members of the Cyprinidae family, females only spawn once a year, scattering large numbers of eggs which are left unguarded and vulnerable to predators (7). However, the female topmouth gudgeon lays several batches of eggs over the breeding season, and the eggs are guarded by the male until they hatch. Each female can lay from a few hundred to a few thousand eggs and may spawn with several different males, laying small batches of a few dozen eggs at a time (2) (3) (4) (7).

The eggs of the topmouth gudgeon are yellowish and very sticky (4) (7), and are laid on a range of substrates, including plants, stones, shells, sand and even boats and plastic pipes (2) (3) (4) (7) (8). The female topmouth gudgeon cleans the substrate before the eggs are laid (2) (3) (4). At temperatures of 20 degrees Celsius, the eggs take about 7 days to hatch. The young topmouth gudgeons initially hide beneath and between stones, only later moving into open water (7). The topmouth gudgeon reaches sexual maturity much faster than most cyprinid species (7), being able to breed at just a year old (2) (3) (4) (8).

The lifespan of the topmouth gudgeon is only around three to four years (4) (7) (8). However, by guarding its eggs this species increases their hatching success, and laying batches of eggs over an extended period makes the young fish less vulnerable if environmental conditions change. Combined with its early sexual maturity, this means that the topmouth gudgeon can reproduce rapidly, which is likely to have contributed to its success as an invasive species (7) (8).


Topmouth gudgeon range

The topmouth gudgeon is native to East Asia, where it occurs from the Amur River basin in Siberia, through the Korean Peninsula and Mongolia to the Pearl River (Zhujiang) basin in southeast China. It also occurs in Taiwan and on some Japanese islands (1) (2) (3) (4) (8) (9).

This small fish has been extensively introduced to areas outside of its natural range, both accidentally and intentionally. The topmouth gudgeon was first recorded in Europe in the 1960s, and has since spread to many European countries (1) (3) (4) (7) (9). It has been introduced to North Africa and parts of central Asia, including Iran, Kazakhstan and Uzbekistan (1) (4) (9), and has also spread to new locations across China and Japan (8).


Topmouth gudgeon habitat

The topmouth gudgeon inhabits a wide variety of freshwater habitats, including ponds, small channels, shallow lakes, irrigation canals, ditches and slow-moving parts of rivers (1) (2) (3) (4) (7) (8). It generally prefers well-vegetated areas with cool, shallow water, which may be either still or slow-flowing (1) (2) (7) (8).


Topmouth gudgeon status

The topmouth gudgeon is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Topmouth gudgeon threats

The topmouth gudgeon is abundant and widespread, and is not known to be facing any major threats (1). Outside its native range, the topmouth gudgeon is regarded as a highly invasive pest species which may potentially compete with and spread diseases to native and farmed fish (2) (3) (4) (7) (8) (9). It may also alter aquatic habitats by preying on invertebrates which normally keep phytoplankton in check, thereby causing an increase in eutrophication of the water (2) (4).

Introductions of the topmouth gudgeon in Europe are likely to have occurred accidentally when the species was inadvertently brought in alongside carp imported from China (3) (4) (7) (8) (9), or when it was introduced as an ornamental species (2) (4) (7). Its adaptability and rapid reproductive rate allow the topmouth gudgeon to spread quickly, while its small size makes it easier for this species to escape into other water bodies (2) (4) (7) (8) (9). The topmouth gudgeon can also spread via eggs laid on boats and angling equipment, or by the escape of individuals used as live bait (2) (4) (7).


Topmouth gudgeon conservation

No known conservation measures are currently in place for this small fish (1). Where it has been introduced and is considered invasive, the topmouth gudgeon may be subject to control measures. For example, in the United Kingdom some populations have been eradicated using the chemical rotenone, while others have been reduced or eliminated by physically removing individuals (2) (5) (6) (11). Other proposed management measures include increasing public awareness of the risks posed by this species, locating all known populations, and undertaking further research into its biology and its effects on other species (4) (11).

Due to the potential threat the topmouth gudgeon poses to native wildlife, keeping or releasing this species without a licence is prohibited in England and Wales (7) (9). In most European countries, it is also illegal to introduce any foreign fish species into open waters (4). Where the topmouth gudgeon has been removed, an increase in the growth and reproduction of native fish has been noted (2) (6).


Find out more

Find out more about the topmouth gudgeon:

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Anal fin
In fish, an unpaired fin on the under surface of a fish, behind the anus.
Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
Dorsal fin
The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).
A process in which a water body is enriched with excessive nutrients (such as nitrogen and phosphorus) resulting in the excessive growth of aquatic plants and the depletion of oxygen, creating unfavourable conditions for other organisms, such as fish.
Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones) and echinoderms.
Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Referring to the visible or measurable characteristics of an organism.
Aquatic plants, usually tiny, that drift passively with water movements.
The production or depositing of eggs in water.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
An area occupied and defended by an animal, a pair of animals or a colony.
A small, rounded, wart-like bump on the skin or on a bone.


  1. IUCN Red List (September, 2013)
  2. GB Non-native Species Secretariat (NNSS): Factsheet - Topmouth gudgeon (September, 2013)
  3. Delivering Alien Invasive Species Inventories for Europe (DAISIE) - Pseudorasbora parva (September, 2013)
  4. NOBANIS: Invasive Alien Species Fact Sheet - Pseudorasbora parva (September, 2013)
  5. Britton, J.R., Davies, G.D. and Brazier, M. (2010) Towards the successful control of the invasive Pseudorasbora parva in the UK. Biological Invasions, 12: 125-131.
  6. Britton, J.R., Davies, G.D. and Brazier, M. (2009) Eradication of the invasive Pseudorasbora parva results in increased growth and production of native fishes. Ecology of Freshwater Fish, 18(1): 8-14.
  7. Pinder, A.C. and Gozlan, R.E. (2003) Sunbleak and topmouth gudgeon - two new additions to Britain’s freshwater fishes. British Wildlife, 15(2): 77-83.
  8. Gozlan, R.E. et al. (2010) Pan-continental invasion of Pseudorasbora parva: towards a better understanding of freshwater fish invasions. Fish and Fisheries, 11(4): 315-340.
  9. Invasive Species Compendium: Datasheets - Pseudorasbora parva (topmouth gudgeon) (September, 2013)
  10. Yalçın-Özdilek, Ş., Kırankaya, Ş.G. and Ekmekçi, F.G. (2013) Feeding ecology of the topmouth gudgeon Pseudorasbora parva (Temminck and Schlegel, 1846) in the Gelingüllü Reservoir, Turkey. Turkish Journal of Fisheries and Aquatic Sciences, 13: 87-94.
  11. GB Non-native Species Secretariat (NNSS) (2013) Invasive Species Action Plan: Topmouth gudgeon (Pseudorasbora parva). GB Non-native Species Secretariat, York. Available at:

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Topmouth gudgeon  
Topmouth gudgeon

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