Darkedged Splitfin, Girardinichthys multiradiatus
Darkedged Splitfin, Girardinichthys multiradiatus. Fish caught in a small lake within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 3.2 cm (1.3 inches). Catch, photograph, and identification courtesy of Ben Cantrell, Peoria, Illinois.
The Darkedged Splitfin, Girardinichthys multiradiatus, is a member of the Splitfin or Goodeidae Family, that is also known as the Golden Sailfin Goodeid and in Mexico as mexclapique de Zempoala. The Sailfin originates from the extended fins in males. Globally, there are three species in the genus Girardinichthys, all of which are found within the freshwater systems of Mexico.
The Darkedged Splitfin has a rectangular fusiform body that tapers gradually on both ends; they are deepest at the origin of their dorsal fin and have a depth that is 28% to 32% of standard length. They vary in color from gray-yellow to bright yellow dorsally and transition to light cream ventrally. Females are drab gold with limited markings. They have a dark spot ventrally just behind their gill openings and several bars on their upper sides that run from the gill cover to the caudal fin base and are more prominent posteriorly. Males are more highly colored than females. They have larger yellow and golden areas and dark anal, caudal, and dorsal fins. Their anal and dorsal fins are also dramatically larger than in females. Their pectoral and pelvic fins are clear. Their head has a deeply rounded snout, disproportionately large eyes set mid-body, and a small terminal mouth that opens in the front and is equipped with incisor-like bicuspid teeth.
The Darkedged Splitfin is a demersal species that is found in quiet, cool, clear, and slow-moving freshwater systems at depths up to 1 m (3 feet) and in temperatures between 12oC (53oF) and 18oC (64oF) over clay, gravel, mud, rock, sand, and silt substrates that are vegetated with numerous aquatic plants. Females reach a maximum of 5.5 cm (2.2 inches) in length while males reach only 3.5 cm (1.4 inches). This species is exceedingly temperature sensitive with only males being born in cold water environments; they produce very small broods with high mortality levels if the water temperature is too warm. They are herbivores and consume primarily vegetable materials. Reproduction is viviparous and involves internal fertilization followed by a sixty day gestation period. Each female gives birth to ten to thirty live young that are 1.2 cm (0.5 inch) in length.
The Darkedged Splitfin is a resident of Mexico’s freshwater systems but has a limited distribution being found within the Mexican Plateau in west-central Mexico in the states of Mexico, Michoacán, and Morelos at elevations above 2,800 m (9,200 feet). The Darkfin Splitfin is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.
The Darkedged Splitfin is most likely confused with the Chapultepec Splitfin, Girardinichthys vivIparus (darker color; smaller mouth).
From a conservation perspective the Darkedged Splitfin is currently considered to be Vulnerable. They have disappeared from several known sites and are now found only in a few small and isolated locations. It is believed that excessive pollution and the introduction of non-native species within their range, including Black Bass and Guppies, has caused their demise. They also suffer from lack of regular monitoring and historical site-specific population data. They are a popular fish with freshwater aquarists due to their beauty and peacefulness and the fact that they are fairly easy to maintain in clean, cool, and neutral to hard water. In tropical temperatures, they are known to become listless, stop breeding, and sometimes expire. During mating they are sexually dimorphic with males exhibiting dramatic showy displays. They will reproduce in captivity.
