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
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

Etymology: 

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

Holotype: 

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

  The Holotype is 71.5mm TL long.

English Name: 
Balsas Splitfin
Mexican Name: 
Mexclapique cola partida
Synonyms: 

Goodea whitei   Meek, 1904

Balsadichthys whitei   Hubbs, 1926

Ilyodon lennoni   Meyer & Förster, 1983

Karyotype: 

  The Karyotype describes the number and appearance of chromosomes during the phase of condensation, classified by the position of the centromere (Levan et al., 1964).

The following abbreviations are employed:

 

M = large metacentric chromsome (a result of Robertsonian fusion)

m = small metacentric chromsome (centromere at medium position)

sm = submetacentric chromsome (centromere at submedian position)

smst = submetacentric-subtelocentric chromosome (continous series)

st = subtelocentric chromosome (centromere at subterminal region)

stt = subtelocentric-acrocentric chromosome (continous series)

t = acrocentric chromosome (centromere at terminal region)

 

The Karyotype of Ilyodon whitei, following Uyeno, Miller & Fitzsimons, 1983:

2n = 48    8st/ 40t

Size: 
The maximum known SL is 101mm (Miller et al, 2005).
Terra typica: 

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

Status after IUCN: 

Critically endangered

Status following other sources: 

Vulnerable; Comment: Some decline since 2000

Distribution and ESU's: 

The Balsas Splitfin is distributed on the Pacific Slope in the upper tributaries of the Río Balsas in the states México, Michoacán and Morelos.

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 I

Río Tamazula II

 

Río Tamazula III

Río Tamazula IV

 

Puente ContlaArroyo Contla

 

Río Naranjo IRío Naranjo II

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.  

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 congeners, so the feeding habits are most probably identical, means mainly herbivorous, grazing from aufwuchs and algae and collecting insects from the surface. 

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).

 

The species Ilyodon cortesae, described in 2000, is thought to belong to whitei by several authors. The status will of course have to be examined, as well as the status of whitei at all due to the narrow relationship of all known forms of Ilyodon.

 

Last phylogenetical results by Domínguez et al revealed that the fish from the Río Coahayana basin, traditionally furcidens, belong to whitei as well as some populations from the Río Armería, destroying more or less all accepted kinds of classification until now, restricting the "real" furcidens to the ríos Ameca, Marabasco and most parts of the Armería. 

Well, comparing at least the population from the Río Tamazula with "typical" furcidens or whitei, it resembles nevertheless in colour, shape, size and behaviour rather furcidens than whitei, so also in this case, the last word isn't spoken.

An interesting excursus to the Poeciliid genus Xiphophorus, where the species clemenciae is definitely a Platy, according to results in comparing the Cytochrome b gene, but testing some nuclear genes, it belongs to the Southern Swordfish around hellerii, a species, it resembles obviously. Following the scientists, this species might be the product of hybridisation between hellerii and a Platy species, most probably maculatus. Maybe a similar process had happened in the genus Ilyodon, so we might have populations of interspecific hybrids in the transition zone (southern Río Armería and Río Coahuayana), and contemplating the very close relationship with little genetic distances of all Ilyodon-populations, the situation might create confusing results.

But like a professor of mine used to say: The situation may be completely different...