Darkedged Splitfin

The dark-edged splitfin varies in shades of yellow, from a grey yellow to bright yellow. G. multiradiatus females reach about 3 inches and males 2.5 inches in length. The species is commonly called the "golden sailfin goodeid" due to their extended fins, especially the males. The males show a notch in the anal fin after the first shorter rays. Additionally, males have longer and broader dorsal and anal fins than the females. The fins of the females are typically clear while the males fins are yellow with a black band on the end. G. multiradiatus females have distinct stripes towards the posterior end of the body.

Girardinichthys multiradiatus can be found in still or slightly moving water in Mexico. The water in which they habitat are mainly considered small lakes, spring-fed ponds, and pools off of colder temperature streams. The dark-edged splitfin prefers bodies of water that range in clear to muddy visibility, and have a bottom of silt, mud, clay, sand, gravel, and rocks. They also prefer water depths to be less than 1 m. The habitat of the dark-edged splitfin also includes a variety of green algae. G. multiradiatus can be found in bodies of water with a pH ranging between 7 and 9, and a dissolved oxygen level between 7 and 10ppm. The preferred water temperature for the highs range from 20–25 degrees Celsius and for the lows range from 10–18 degrees Celsius.

G. multiradiatus tend to school with each other. They detect nearby movements using a mechanosensory system known as their lateral line system. They use this system to detect many behaviors such as schooling, rheotaxis, and predator-prey interaction. Not only do they use mechanosensory, they also use water movements to show social behaviors.