How to Identify Mexican Tetra

To identify Mexican Tetra (Astyanax mexicanus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Surface forms are silvery with a prominent dark lateral stripe extending from the operculum to the caudal peduncle. Fins are typically translucent. Cave forms are depigmented, appearing pinkish-white, and lack eyes (anophthalmic).

Scale type

cycloid

Mouth position

terminal

Distinctive features

Presence or absence of eyes (surface vs. cave forms), Pigmentation (present in surface forms, absent in cave forms), Adipose fin present, Lateral line system highly developed, especially in cave forms

Dorsal fin

Single dorsal fin, typically with 10-11 rays.

Tail fin

Forked caudal fin, symmetrical.

Pectoral fin

Paired pectoral fins, relatively small.

Distinctive fins

Adipose fin present between the dorsal and caudal fins, characteristic of Characidae.

Identification Tips

1. 1

   Eyes and Pigmentation

   The most obvious distinguishing feature is the presence of eyes and silvery pigmentation in surface forms versus the complete absence of eyes and pigmentation (pinkish-white color) in cave forms.

2. 2

   Lateral Stripe

   Surface forms possess a distinct dark lateral stripe. This is absent in cave forms due to depigmentation.

3. 3

   Adipose Fin

   The presence of a small, fleshy adipose fin between the dorsal and caudal fins is a key characteristic of the Characidae family, to which Astyanax mexicanus belongs.

4. 4

   Body Shape

   Both forms have a moderately compressed, fusiform body shape, typical of many characins.

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