Butterfly Splitfin

As its common name implies, it is indeed quite an attractive fish. In a dominant mature male specimen the large dorsal fin is like the caudal fin washed with black. A yellow band stretches along the caudal's back margin. The body of both sexes is ochre, with silvery sides and a brownish back, which in males usually have numerous glittering metallic scales. Females and immatures having black dots on the sides and ochre fins. The fins of males intensify in color when they are excited, and depending on their mood, they can show more or less strongly a black band along the side. For the first two weeks or so after birth, the young are entirely silvery. Males can also be told apart from females because their anal fin's front part splits off and transforms to a blunt, flexible andropodium used for mating. As usual in live-bearers, males are the smaller sex, reaching some 3 in (7–8 cm) total length at best, with females being able to grow up to 4 in (10 cm) under good conditions.

In its former natural habitat, the bedrock is limestone, resulting in a hard and alkaline water with a general hardness of 6-10 dGH, while the temporary (carbonate) hardness is usually between 7 and 11°. The pH is around 8, and temperature varies little between the seasons, but ranges between about 70 and 85 °F (20 and 30 °C) between day and night. The vegetation is largely limited to algae and Ceratophyllum hornworts. The remnant wild population coexists with the native blackfin goodea (Goodea atripinnis) and Lerma live-bearer (Poeciliopsis infans), as well as with the common molly (Poecilia sphenops), Oreochromis tilapias, and the bluegill (Lepomis macrochirus) which presumably have all been introduced. Among groups of A. splendens, a loose dominance hierarchy develops, in particular in confined environments. Males chase each other about, with the dominant male(s) showing the most splendid coloration. Submissive males will try to retreat from attacks, typically towards the surface, and may shake their head as a calming signal.

Like other Goodeidae, butterfly splitfins mate by internal fertilization and spawn fully developed young. The females become sexually mature at about six months of age and can give birth every six to 10 weeks according to the water temperature and the condition of the fish. …