Montana Field Guide

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Montana Field Guides

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- Kingdom - Animals - Animalia
  - Phylum - Vertebrates - Craniata
    - Class - Fish - Actinopterygii
      - Order - Killfish / Mollies - Cyprinodontiformes
        
        Family - Livebearers (Mosquitofish / Mollies / Swordtails) - Poeciliidae
        
        Species - Shortfin Molly - Poecilia mexicana

Shortfin Molly - Poecilia mexicana

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Non-native Species

Global Rank: G5
State Rank: SNA

Agency Status
USFWS:
USFS:
BLM:

External Links

General Description

This tropical aquarium fish is an illegally released pet fish. The native range is southeastern United States, Mexico, and Central America.

Diagnostic Characteristics

Specimens from Montana waters have been nearly all black or heavily blotched with black on body and fins. Some have orange on tail fin.

Observations in Montana Natural Heritage Program Database

Number of Observations: 5

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Relative Density

Recency

(Observations spanning multiple months or years are excluded from time charts)

Habitat

Can exist in Montana only in warm springs of ponds and streams resulting from these.

Food Habits

Diet varied. Feeds on both plant and animal matter. Vascular plants and mosquito larvae are important items in the diet.

Reproductive Characteristics

Reaches Sexual maturity at 1.5 - 2 in. in length. Under suitable conditions may produce several broods a year. Fertilization internal; young born alive.

Stewardship Responsibility

References

Additional ReferencesLegend: View Online Publication
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- Joslin, Gayle, and Heidi B. Youmans. 1999. Effects of recreation on Rocky Mountain wildlife: a review for Montana. [Montana]: Montana Chapter of the Wildlife Society.
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Ferns and allies

Conifers

Flowering Plants (Dicots)

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Citation for data on this website:
Shortfin Molly — Poecilia mexicana. Montana Field Guide. Montana Natural Heritage Program and Montana Fish, Wildlife and Parks. Retrieved on November 3, 2025, from https://FieldGuide.mt.gov/speciesDetail.aspx?elcode=AFCNC04030