Poecilia sphenops Valenciennes, 1846

Size

Poecilia sphenops Valenciennes, 1846 can reach 8.4 cm (3.3 in) in standard length or 10 cm (3.9 in) in total length, though most individuals are smaller. This species is sexually dimorphic: females grow approximately 1 cm (0.39 in) larger than males.

Male Growth

Males, which display more intense coloration than females, stop growing almost entirely once their gonopodium finishes developing.

Native Range Overview

Poecilia sphenops is native to both the Atlantic and Pacific slopes of Mexico and northern Central America.

Atlantic Slope Distribution

On the Atlantic slope, its range extends from the Palma Sola River in the north south to the Coatzacoalcos River basin and the headwaters of the Grijalva River.

Pacific Slope Distribution

On the Pacific slope, it occurs from the middle of the Río Verde basin in the Mexican state of Oaxaca to western Honduras and northern Guatemala.

Co-occurrence with Related Species

It is often found living alongside Poecilia mexicana. In short coastal streams, P. sphenops typically occupies upstream habitats, while P. mexicana occupies downstream habitats.

Introduction Pathways

P. sphenops has been introduced outside its native range via escapes from aquarists and fish farms, as well as intentional releases.

Naturalized Non-native Range

It is considered naturalized in the U.S. states of Montana and Nevada, and also in Puerto Rico.

Non-native Population Uncertainty

Populations have also been reported in California and Arizona, but some or all of these non-native populations may actually belong to another species in the P. sphenops species complex. At the same time, some introductions previously attributed to P. mexicana may actually be P. sphenops.

Post-establishment Dispersal

After this species establishes in a new area, it disperses and colonizes new sites on its own without additional human assistance.

Habitat Types

P. sphenops lives in both freshwater and brackish habitats, including rivers, ponds, lagoons, roadside ditches, and creeks. It is especially widespread in creeks, and can be found in both lowland and upland areas.

Water Flow Requirements

It occurs in stagnant water as well as water with slight or moderate flow.

Water Characteristics

The water it inhabits can be clear, turbid, or muddy, and is typically no deeper than 1 m (3 ft 3 in).

Substrate Types

Habitat substrates can include marl, clay, silt, often deep mud, rock, or bedrock.

Aquatic Vegetation

Some of its habitats have no aquatic vegetation at all, while others have abundant algae (such as Chara) and plants including Lemna, Nasturtium, fine-leaved Potamogeton, Sagittaria, and Typha species.

Temperature Tolerance

When acclimated to temperatures between 20–35°C, P. sphenops can survive in temperatures ranging from 10.8–11.8°C to 38.8–39.5°C.

Reproductive Strategy

P. sphenops is a livebearing fish that produces up to 150 young after a one-month gestation period. Young P. sphenops have been recorded between January and August, which indicates the species reproduces through most of the year.

Habitat Segregation by Age

In rivers, adult P. sphenops gather near the banks, while fry remain in very shallow water.

Mating Behavior

Like other members of the P. sphenops species complex, this species does not perform courtship displays. Instead, males sneak up on females and force copulation.

Male Post-maturity Lifespan

Males do not live long after reaching sexual maturity.

Sex Ratio

As with other poeciliids, P. sphenops populations usually contain more females than males.

Male Mortality Drivers

Males are more prone to stress and metabolic aging, are less resistant to unfavorable environmental conditions, and are easier for predators to catch due to their smaller size and more conspicuous coloration.