How to Identify Topmouth Gudgeon

To identify Topmouth Gudgeon (Pseudorasbora parva), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Dorsal side is typically olive-brown to grey, fading to silvery-white on the belly. A distinct dark lateral stripe often runs from the snout to the caudal fin base, sometimes with a series of dark spots above it. Fins are generally translucent or slightly dusky. Breeding males may develop nuptial tubercles on the head and snout.

Scale type

cycloid

Mouth position

superior

Distinctive features

Small, slender body, typically reaching 8-12 cm (3-5 inches) in length, with a maximum recorded length of about 15 cm., Relatively large eyes., Superior (upward-pointing) mouth, adapted for surface feeding., A single, short dorsal fin., Lateral line usually complete, with 34-39 scales., Absence of barbels.

Dorsal fin

Single, short dorsal fin with 3 unbranched and 7 branched rays.

Tail fin

Forked caudal fin.

Pectoral fin

Pectoral fins are relatively short, with 1 unbranched and 11-13 branched rays.

Distinctive fins

Pelvic fins are abdominal, with 1 unbranched and 7 branched rays. Anal fin has 3 unbranched and 5 branched rays.

Identification Tips

1. 1

   Mouth Position

   The most distinguishing feature is its superior (upward-pointing) mouth, which is unique among many small cyprinids in its introduced range.

2. 2

   Lateral Stripe

   Look for a prominent dark lateral stripe running along the flank, often with a series of darker spots above it.

3. 3

   Absence of Barbels

   Unlike true gudgeons (Gobio gobio), the Topmouth Gudgeon lacks barbels around its mouth.

4. 4

   Size and Body Shape

   Small, slender body, typically not exceeding 15 cm in length.

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