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

[8][5] P. sphenops frequently occurs together with P. mexicana, but in short coastal streams the former tends to occupy upstream and the latter downstream habitats.

[9][10] It is considered naturalized in the US states of Montana and Nevada as well as in Puerto Rico and reported from California and Arizona, but some or all of these populations may turn out to represent another species of the P. sphenops complex.

Some of the habitats are devoid of vegetation, while in others algae (e.g. Chara) and plants such as Lemna, Nasturtium, fine-leaved Potamogeton, Sagittaria, and Typha species are abundant.

[11] P. sphenops is highly adaptable in terms of diet, utlizing a variety of food sources in different habitats.

[5] Different populations of the species have been recorded browsing on filamentous algae, filtering phytoplankton, rotifers, and crustaceans, preying on protozoa and insect larvae, or feeding chiefly on detritus.

[5] As with other members of its species complex, P. sphenops does not exhibit courtship display; instead, males sneak up to females and force copulation.

Males are more susceptible to stress and metabolic aging, less resistant to adverse environmental conditions, and predated on more easily due to their smaller size and more conspicuous colors.

[18] The fish are exploited in artesian fisheries for human consumption in parts of the state of Oaxaca, and are suitable for aquaculture because of their thermal adaptability.