Butterfly Splitfin

Butterfly Splitfin, Ameca splendens

The Butterfly Splitfin, Ameca splendens, whose common Spanish name is mexclapique mariposa, is a member of the Splitfin or Goodeidae Family, known collectively as mexclapiques in Mexico. This fish is also known as the Butterfly Goodeid. It is the sole global species in the genus Ameca.

The Butterfly Splitfins have elongated and narrow bodies with a pointed snout and an elongated caudal peduncle. They are sexually dimorphic. Males are olive-brown dorsally and transition to golden yellow ventrally; they are brilliantly colored with metallic bluish to turquoise reflections on their scales; their anal, caudal, and second dorsal fins have a wide black stripe mid-fin and a wide yellow-orange margin. Females are drab in color; they are greenish-yellow and have blue reflections on their scales; they have pale fins and numerous rows of brown spots that form random lines along their sides. Juveniles have a row of two to seven spots below the mid-line on their sides and a large spot at the base of their caudal fin. Their head has a short pointed snout and a large terminal mouth equipped with bifid teeth. They have mid-sized eyes set on the mid-line and multiple gill rakers. Their anal and dorsal fins are set well back on the body and their caudal fin is rounded.

The Butterfly Splitfins are found demersal in clear warm springs with slight current flows and consistent year-round temperatures between 20oC (70oF) and 30oC (85oF); they are found at depths up to 5 feet in gravel, mud, rock, and sand substrate, and where aquatic plants proliferate. Females, which can become massive when pregnant, reach a maximum length of 12.0 cm (4.7 inches); they are larger than males, which reach a maximum length of 8.0 cm (3.1 inches). They are diurnal herbivores and feed on algae, bloodworms, diatoms, insects, and invertebrates. Reproduction is viviparous and involves internal fertilization followed by a gestation period lasting 55 to 60 days. Each female gives birth to 5 to 30 live young measuring 1.5 cm (0.75 inch), which are able to survive on their own.

In Mexican waters the Butterfly Splitfins have historically had an exceedingly limited distribution being found in a ten square mile area west of Guadalajara in the freshwater systems within the Mexican Plateau in west-central Mexico such as the Río Ameca and Río Teuchitlán in the state of Jalisco.

The male Butterfly Splitfin is straightforward to identify and cannot easily be confused with other species. The female Butterfly Splitfin is very similar to the Jeweled Splitfin, Xenotoca variata and the Polka-dot Splitfin, Chapalichthys pardalis, however, both lack the black caudal fin stripe.

The Butterfly Splitfins were once a popular aquarium fish but they require large tanks, frequent water changes, strictly controlled temperatures, and the presence of green algae. They are strong swimmers that can be found in groups of three to five males and three to seven females. They are prolific breeders that generate an overabundance of offspring quickly generating overcrowded conditions. They are also unfriendly and attack tank mates that are different from them, however, they are not cannibalistic. They are one of the few Splitfins that breeders have been able to manipulate to produce lighter colored white-finned males. From a conservation perspective, they are currently listed as Extinct In The Wild, which is not 100% correct, as evidenced by the catches below and by a documented feral population living in southeast Nevada presumably originating from an aquarium escape. They have disappeared from several known sites and are now found only in a few small and isolated new locations. The water habitat in some parts of their range has experienced a staggering amount of degradation during the 20th century and they are heavily preyed upon by various birds and recently introduced non-native fish including Black Bass, Guppies, Largemouth Bass, Sunfish, and Tilapia.

Butterfly Splitfin, Ameca splendens, Female. Fish caught in the Rio Teuchitlán within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 8.5 cm (3.3 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.

Butterfly Splitfin, Ameca splendens, Male. Fish caught in the Rio Teuchitlán within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 6.5 cm (2.6 inches). Catch, photo, and identification courtesy of Ben Cantrell, Peoria, IL.

Butterfly Splitfin, Ameca splendens, Male. Fish caught in a small lake within the Mexican Plateau in west-central Mexico, Michoacán, February 2017. Length: 7.0 cm (2.8 inches). Catch, photo, and identification courtesy of Ryan Crutchfield, Tampa, FL.