How to Identify Goodeid

To identify Goodeid (Girardinichthys viviparus), look at these key features.

Physical Characteristics

Body shape

elongated

Coloration

Males typically exhibit more vibrant coloration, often with iridescent blue, green, or yellow hues on their flanks and fins, especially during breeding. Females are generally duller, with a silvery-brown to olive-green body. Both sexes may have faint vertical bars or spots. The caudal fin often has a dark margin.

Scale type

cycloid

Mouth position

superior

Distinctive features

Sexual dimorphism: Males are smaller and more colorful, with a modified anal fin (andropodium) for internal fertilization. Females are larger and plumper., Relatively large eyes., Small, upturned mouth.

Dorsal fin

Single, relatively short-based dorsal fin positioned posteriorly, often with 10-12 rays.

Tail fin

Rounded to slightly emarginate caudal fin.

Pectoral fin

Small, rounded pectoral fins.

Distinctive fins

Males possess a highly modified anal fin (andropodium) where the anterior rays are separated and thickened, used for sperm transfer. Females have a normal anal fin.

Identification Tips

1. 1

   Sexual Dimorphism

   Males are smaller (up to 5 cm TL) and more brightly colored, with a distinct, modified anal fin (andropodium). Females are larger (up to 7 cm TL), plumper, and less colorful, with a normal anal fin.

2. 2

   Body Shape and Coloration

   Robust, somewhat elongated body. Males often show iridescent blues/greens/yellows, especially on fins and flanks. Females are olive-brown to silvery. Both may have subtle barring.

3. 3

   Mouth Position

   Small, upturned mouth, indicating a surface-feeding habit.

4. 4

   Geographic Location

   If encountered in the wild, its presence in the Central Mexican Plateau, particularly the Lake Pátzcuaro region, is a strong indicator.

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