The Little Colorado River Basin contains a variety of aquatic habitat types and is prone to dramatic seasonal and yearly fluctuations in water quality and quantity. As would be expected for a species adapted to fluctuating physical conditions, the spinedace occurs in a variety of habitats. It is unclear whether occupancy of these habitats reflects the local preferences of the species or its ability to tolerate less-than-optimal conditions. Spinedace use both mountain streams and lower-gradient streams and rivers. Residual pools and spring areas are important refuges during periods of normal low water or drought.

Optimal habitat for the Little Colorado spinedace includes clear, flowing pools with slow to moderate currents, moderate depths and gravel substrates. Spinedace use undercut banks, and or, boulders for cover. Water temperatures in occupied habitats ranged from 14.5 to 25.6 degrees Celsius (58 to 78 degrees Fahrenheit).
 

Spinedace are omnivorous, and food items include chironomid larvae, commonly known as midges, flies, filamentous green algae and crustaceans.

Little Colorado spinedace have large eyes and a shortened rounded snout. The pectoral fin on males is larger than females, but both males and females are generally the same size. The spinedace gets its name from the moderately high and acute dorsal, or back fin that is also referred to as the spine.

Sexual dimorphism is minimal, with males and females reaching generally the same length. Spinedace are 6 to 8 millimeters (0.24 to 0.31 in) total length when they hatch and reach 25 millimeters (less than 1 in) in one month. After 10 weeks, fish are 50 to 60 millimeters (2 to 2.4 in), reaching 75 to 80 millimeters (3 to 3.1 in) by the end of their first year.

Measurements

Length: Generally less than 100 millimeters (roughly 4 in) total length, but can be larger. 
 

There are minimal color differences between male and female Little Colorado spinedace. Generally, the fish has an olive-green, bluish or lead gray back and olive-green upper sides. The underside is watery-yellow to white. Irregularly distributed, fine, black puncticulations, meaning that they give a pepper-like effect, overlie the silvery sides. Except for pigmentation along the fin rays and on the interradial membranes, or membranes connecting rays and spines in the fins, near the bases of the fins, both paired and unpaired fins are largely clear. There is a conspicuous, cream-colored spot at both the origin of the dorsal, or back, fin and near the bases of the terminal rays of this fin.

During spawning the bases of the paired fins in males turn an intense reddish-orange or appear to have a wash of weak yellow or orange. Females develop a watery yellowish or reddish-orange at the bases of the paired fins.
 

Spinedace are late-spring to early-summer spawners although some females contain mature eggs as late as October. Spinedace spawn in slow currents over cobbles with roughly, four to eight, males attending each female. Female fish randomly deposit eggs over the stream bottom or on aquatic vegetation or other organic debris.

Little Colorado spinedace generally live about three years.