Ilyodon whitei (incl. cortesae & lennoni)

Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
Ilyodon whitei
English Name: 
Balsas Splitfin
Mexican Name: 
Mexclapique cola partida
Original Description: 

  MEEK, S. E. (1904): The fresh-water fishes of Mexico north of the Isthmus of Tehuantepec. Publication. Field Columbian Museum 93, Zoological Series 5: pp 137-138

Holotype: 

  Collection-number: Field Columbian Museum, Cat. No. FCM-4547.

  The Holotype is 71.5mm TL long.

Holotype of Ilyodon whitei

Terra typica: 

  The Holotype comes from upper tributaries of the Río Balsas near Yautepec in Morelos.

Etymology: 

  This species is named for E.A. White of the city of Mexico, in recognition of many favours, Meek received through his courtesy.

Synonyms: 

Goodea whitei   Meek, 1904

Balsadichthys whitei   Hubbs, 1926

Ilyodon lennoni   Meyer & Förster, 1983

Ilyodon cortesae   Paulo-Maya & Trujillo-Jiménez, 2000

Distribution and ESU's: 

  The Balsas Splitfin is endemic to the Mexican federal states of Michoacán, Mexico, Morelos, Guerrero and Pueblo. It is known from the upper Río Coahuayana drainage (sections Río Tamazula and Tuxpán) and affluents, eventually also from the Río El Cajón, an easterm affluent of the Río Naranjo (name of the middle section of the Río Coahuayana), and from most of the northern reaches of the Río Balsas, starting in the E with the ríos Atoyac, AmacuzacTepecuacuilco and Cocula in the Eastern Río Balsas basin, then the ríos OxtotitlánPalos AltosCutzamala, the arroyos San Lucas and Grande and the Río Chiquito in the Central Río Balsas basin, and finally the Río Grande, western Río Balsas basin. According to its occurence in several basins, five subpopulations can be inferred: The Río Amacuzac subpopulation (type subpopulation), the Río Atoyac subpopulation, the Upper Río Cutzmala subpopulation, the Upper Río Coahuayana subpopulation and the Western Río Balsas subpopulation. The underlined names are the ones officially used by the Instituto Nacional de Estadística y Geografía; nevertheless, other ones might be more often in use or better known and therefore prefered.

 

  ESU ist short for Evolutionarily Significant Unit. Each unit expresses an isolated population with different genetic characteristics within one species.  ESU's can be defined by Molecular genetics, Morphology and/or Zoogeography and help in indicating different phylogenetic lineages within a species. The abbreviation for an ESU is composed of the first 3 letters of the genus, followed by the first 2 letters of the species name and an ongoing number in each species.

 

  In Ilyodon whitei, we have the situation, that the five ESU's we distinguish do not match with the last phylogenetic results (Beltrán-Lopez et al., 2017). We try here to bring together both systems until the situation is cleared. Ilywh1 is one ESU with a polyphyletic origin. Fish from the lower Río Coahuayana basin (including Ilyodon xantusi) represent Ilyodon furcidens, whereas fish from the upper Coahuayana river Ilyodon whitei.  This population forms Clade D within Ilywh1, whereas fish from the western Balsas present Clade E within the same ESU. So these both populations represent different phylogenetic lineages. Additionally, the ESUs Ilywh2 from the Río Tacambaro ("cortesae") and Ilywh3 from the Río Chacembero ("lennoni") belong phylogenetically to Clade E. Confusing situation, we have to confess. Anyway, we prefer to keep these two populations as separate ESU's due to situation, they were kept as distinct species for a while. Ilywh4 encompasses fish from the middle Balsas - basin (ríos Amacuzac, Cuautla, Cuernavaca and Cútzmala), subclade B2 sensu Beltrán-Lopez, whereas Ilywh5 the ones from the eastern Balsas - basin (Río Atoyac and creeks in vicinity) subclade B1respectively .

 

  Maximum Extent of Occurence of Ilyodon whitei:

Maximum EOO of Ilyodon whitei

Status : 

  International Union for Conservation of Nature (IUCN): critically endangered

 

  Conservation status and population trends of Mexican Goodeids (Lyons, 2011): vulnerable/declining – As I define it, this species is limited to the Balsas River basin, where it occurs in about 12 different areas. Specimens from a tributary to the Balsas River near Ciudad Altamirano in the state of Guerrero were described as a separate species, I. lennoni (Meyer and Forster 1983), but I and most other ichthyologists (e.g., Doadrio and Domínguez-Domínguez 2004; Domínguez-Domínguez et al. 2005b; Miller et al. 2005) do not consider this name to be valid. Many populations of I. whitei have declined or disappeared over the last 25 years, largely because of predation by or competition from non-native fish species (e.g., Contreras-MacBeath et al. 1998). Non-native species now dominate many areas of the Balsas River basin.

Ilyodon cortesae: critically endangered/stable? – This species was recently described (Paulo-Maya and Trujillo-Jimenez 2000), and is known from only three nearby locations in the Tacámbaro River drainage in the upper Balsas River basin. However, some ichthyologists question the validity of this species and suggest that it may be merely a variant of I. whitei (Miller et al. 2005; Omar Domínguez-Domínguez, personal communication). Little is known about the overall distribution and abundance of I. cortesae, which is found in a remote and difficult-to-access area, but known populations are small and localized.

 

  NOM-059-SEMARNAT-2010: no categoría de riesgo (no category of risk)

Habitat: 

  The habitats are similar to the ones of Ilyodon furcidens, means pools and riffles of clear to turbid streams, over substrates of sand, silt, mud, gravel, rocks and boulders. The currents are usually slight to swift. Vegetation can be absent or made of green algae, Potamogeton and Ceratophyllum. The preferred depth is less than 1.3m.

Río Tamazula Rio Contla

Presa Caltzontzín

Ri­o Naranjo

Biology: 

  Miller (2005) wrote, that the occurrence of young in collections suggests that the reproduction occurs during the latter part of the dry season in March and April.

Diet: 

  Teeth, gut and dentition is similar to its congener, so the feeding habits are most probably identical, means mainly herbivorous, grazing from aufwuchs and algae and collecting insects from the surface. Two trophic types can be distinguished (by their mouth) in this species: One with a narrow mouth (being suggested to be insectivore or planktivore), and one with a broad mouth (being suggested to feed from aufwuchs and algae). Both types have been seen feeding in the habitat from aufwuchs, the narrow-mouthed form additionally from the surface (Kingston, 1979). The broad mouth form was originally described as Ilyodon xantusi. The gut of both types is long and suggests herbivorous feeding habits.

Size: 
The maximum known standard length is 101mm (Miller et al., 2005).
Colouration: 

  The ground colouration of Ilyodon whitei is mostly light brown or grey, in some populations tending to yellow. The upper part of the body is darker than the lower part, the scales have its posterior portion darker giving the fish a finely speckled appearance. A narrow blackish lateral band, extending from above the opercle nearly to the base of the caudal fin, is composed of a lot of small dark dots in males, females often have this band splitted into the single dots. Both sexes have no or very few dots in the fins, but darker areas can be found sometimes, mainly as a short bar in the anal fin. The base of the caudal fin is dotted with several transverse rows of dark dots and the caudal fin itself shows a dark submarginal band followed by a yellowish terminal band in the male gender. Males show a metallic-yellowish or bluish mirror on the sides, sometimes even females can show a hint of it. Many fins show iridescent light parts.  

Remarks: 

  This species is widely distributed. Its eastern habitats are reaching nearly the height of Mexico City, westwards this species reaches even the Río Tamazula. Looking at its distribution along the Río Balsas basin, it is conspicuous, that it inhabits only the right tributaries of this river. This might be caused by river piracy of the Río Balsas, taking over waters from a river originally flowing much more northwards of the Balsas to the Río Coahuayana basin. Strata movement may have raised a new mountain range with redirecting former waters of this ancient river being now tributaries of the Balsas river, that is (mainly) free of Ilyodon.

 

  In 1983, Meyer and Förster described Ilyodon lelloni in honour of the famous British musician and former member of the "Beatles", John Lennon. Following the describers, this species should be forming a complex with Ilydodon xantusi in contrast to a complex formed by furcidens and whitei. However, the noticed differences in dentition and trophotaenial structure are not big enough to separate lennoni from whitei. Furthermore, a described gender related pair of chromosomes seemed to rather reflect differences that can be found routinely in condensation and fixation of chromosomes than a real chromosomal heteromorphism (Turner, 1985).

 

 Ilyodon cortesae,  that was described by Paulo-Maya & Trujillo-Jiménez is differing from other populations of Ilyodon whitei by its strongly convex cephalic profile, its small size, the thinner caudal peduncle, more scales in the longitudinal series, form and size of the neural prezygapophyses of the caudal vertebrae, the strongly bifid teeth and the disposition of the pores of the lateral line of the preorbital system. Nevertheless phylogenetical results are clear, that the populations from the Río Tacambaro belong to whitei, too.