Mexican stoneroller
The Mexican Stoneroller belongs to family Cyprididae, and its scientific name is the Campo stoma ornatum. There are three species in this genus, which all have morphologically similar characteristics: the anomalum, the oligolepis, and the ornatum. The ornatum is the only fish from this group endemic to Arizona waters.
Description
The Mexican Stoneroller has a very stout body throughout its life with a very large head and snout. The mouth is very unique containing cartilaginous sheaths behind its teeth, but the size of the mouth is usually very small. The fish’s length can range anywhere from 12.7 to 15cm, however 15cm is rare. They have small scales that run along the lateral line, much like the Gila and Yaqui Longfin Daces. Stoneroller scales can sometimes form arches on its back. Sexual selection has dictated exaggerated male characteristics, which include larger heads and pre-dorsal areas of more successful mating animals. These fish have color patterns with lighter bottoms and darker backs, with a distinct black stripe along the lateral line. They also have a somewhat blotched appearance.
Distribution in Arizona
The Stoneroller has a very wide distribution ranging from Rucker Canyon, all the way to the Chircahua Mountains. Several specimens were also introduced at San Bernadino Creek for ecological reasons. The San Bernadino Wildlife Refuge is trying to preserve the endangered Stoneroller by reintroducing it at Whitewater Creek near Black Draw. They have been found as far as the Rio Yaqui drainage in Mexico and the Rio Grande River in Texas. Elevation preferences range from 2600 to 6500 feet; these fish are ecological restricted to these altitudes.
Habitat
Stonerollers prefer shallow waters near gravel and stone substrates, and larger adults can be found in sandy-bottomed streams. They will use under-covered banks to protect themselves from predators and humans. The biotic community of the fish is primarily the Montane Conifer Forest in the Chiricahua Mountains. They are restricted to higher elevations because of their restricted diet of detritus and algae that thrive in colder waters. Aquatic insects are also part of the fish’s diet, if these primary sources are not available due to droughts.
Reproduction
Very few studies of the reproduction of this species have been conducted, leaving a limited amount of information about their patterns. We do know that these fish are capable of changing the colors on their fins during breeding. The color changes are more dramatic in males, due to sexual selection and female mate choice. The winter and late spring months seem to be the primary times in which the bulk of spawning occurs. Stonerollers use their tubercles as weapons during male-to-male competition, and also to stimulate and attract females. The name Stoneroller was given because males excavate breeding areas by rolling stones with their heads to invite the female. This also helps them defend against rivaling males.
Biology and Conservation
The cartilaginous sheaths on their jaws are used for scraping algae and detritus along the gravel and stones within the habitat. An unusual amount of sexual selection has occurred in this species for unknown reasons, and large amounts of energy are expended in male competition and mating success because of this selection. This extra energy is perhaps wasted, and it could be contributing to the decline in fitness and ultimately the disappearance of the species. Specimens are declining rapidly in Rucker Canyon along with San Bernardino Creek, however numbers in Texas and lower Mexico are remaining stable. The Arizona Game and Fish Department placed the species on Endangered Status in 1988, and it still remains. Aquifer pumping, reduction in stream flows, and predation from non-native green sunfish, are all major contributing factors to the decline of the species according to Nature Serve (2002). The San Bernardino Ranch has current plans to reintroduce new specimens in attempt to recharge the Stoneroller, and other projects involve federal habitat preservation.