Pseudoxiphophorus bimaculatus (Heckel, 1848)

Taxonomic Classification

Pseudoxiphophorus bimaculatus is a small freshwater livebearing fish species belonging to the Poeciliidae family.

General Coloration

In terms of coloration, individuals of this species often have green iridescence around their operculum, subtle black and yellow tones on their scales and fins, and a distinct black spot on the upper portion of the caudal fin.

Caudal Fin Spot

This black spot is a characteristic feature of the species, and it is present in both males and females.

Caudal Fin Structure

Unlike many other Poeciliidae species, P. bimaculatus has no sword-like extension or protrusion on its caudal fin.

Sexual Dimorphism Gonopodium

The only clear sexual dimorphism between male and female P. bimaculatus is the modified anal fin found in males, called a gonopodium.

Male Coloration Risk

Males may sometimes have brighter coloration than females, which can make them more vulnerable to predation.

Female Size Average

Females typically grow larger and heavier than males, with an average standard length of approximately 6.6 cm.

Female Size Maximum

Larger female individuals have been recorded, reaching a total length of around 9.1 cm and a maximum weight of 9.96 g.

Native Range Overview

P. bimaculatus is native to Central America and southern Mexico.

Central America Native Distribution

It is confirmed native to Belize, Guatemala, Nicaragua, and Honduras.

Mexico Regional Status Variation

In Mexico, its status as native, non-native, or invasive varies by region.

Mexico Confirmed Native States

The IUCN Red List officially recognizes it as native to the Mexican states of Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz, and Yucatán.

Mexico Introduced Range

It has been introduced to the Mexican states of Guerrero, Jalisco, and Michoacán, and has also been reported in Guanajuato, Querétaro, and the more northerly state of Tamaulipas.

Reproduction Organ Use

Reproduction in Pseudoxiphophorus bimaculatus is carried out using the male gonopodium.

Mating Behavior

The species does not perform courtship displays; instead, males make quick reproduction attempts, transferring sperm to females via gonopodial thrusts.

Spawning Period

Spawning occurs year-round, but is most common during the summer months and rainy season.

Average Fecundity

Female P. bimaculatus produce an average of around 31 fertilized eggs.

Fertility Drivers

Fertility is linked to environmental conditions including pH, dissolved solid content, and vegetation presence, as well as female size: larger females typically produce more embryos.

Reproductive Strategy

P. bimaculatus is iteroparous, meaning it can reproduce repeatedly and continuously throughout its lifespan.

Sexual Maturity Size Thresholds

In populations of this species, females grow larger but reach sexual maturity later than males: females reach sexual maturity at a standard length of around 27 mm, while males reach it at around 22 mm.

Population Sex Ratio Range

Population sex ratios are usually female-biased, ranging from 2 females per 1 male to 6 females per 1 male.

Sex Ratio Skew Drivers

This skew is often caused by environmental conditions, as males are more vulnerable in areas with higher predation and higher temperatures.

Sex Ratio Balance Conditions

Sex ratios are more balanced in habitats where these risks are lower.

Environmental Reproduction Tolerance

P. bimaculatus is able to reproduce across a wide range of environmental conditions.

Invasion Success Factors

Combined with its iteroparous life history and naturally female-biased population ratios, this ability has allowed the species to become established and thrive in ecosystems outside its native range.