"Xenotoca" melanosoma

Xenotoca melanosoma
Xenotoca melanosoma
Xenotoca melanosoma
Xenotoca melanosoma
Original Description: 

  FITZSIMONS, J. M. (1972): A revision of two genera of Goodeid fishes (Cyprinodontiformes, Osteichthyes) from the Mexican Plateau: Copeia 4: pp 728 - 756

Etymology: 

  The specific greek epithet melanosoma means "dark body", a diagnostic feature of this species (melano = black, soma = body).

Holotype: 

  Collection-number: University of Michigan Museum of Zoology, Cat. No. UMMZ-189077.

  The Holotype is a mature male of 65.5mm SL, collected by R. R. Miller and H. L. Huddle, 03.04.1968.

English Name: 
Black Splitfin
Mexican Name: 
Mexclapique negro
Synonyms: 

Xenotoca melanosoma    Fitzsimons, 1972

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 "Xenotoca" melanosoma, following Uyeno, Miller & Fitzsimons, 1983:

2n = 48    8st/ 40t    

Size: 
The maximum known SL is 85mm (Miller et al, 2005).
Terra typica: 

  The Holotype was collected in the Río Tamazula, just below HW 110 bridge, 5km S of the town of Guzmán turnoff in the state of Jalisco.

Status after IUCN: 

  not assessed

Status following other sources: 

   assessed together with "Xenotoca cf. melanosoma: Threatened; Comment: Stable since 2000.

   Following Domínguez (pers. com.2016): Critically endangered or Extinct in the wild

Distribution and ESU's: 

  This species comes from the Pacific Slope, inhabiting the ríos Ayuquila (Río Armería basin), Tamazula and Tuxpán (Río Coahuayana basin). Recent studies say, that populations from the ríos Ameca and Grande de Santiago, as well as from the endorheic basins of Etzatlán, Magdalena, Zacoalco, San Marcos, Atotonilco and Zapotlán belong to a distinct and not yet described species (Domínguez-Domínguez, pers. comm. 2011; Mar-Silva, pers. comm. 2013).

 

  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 "Xenotoca" melanosoma - with respects to the population from the Río Ayuquila - we are by now not able to distinguish different ESU's. It may be that both known populations will have to be treated as separate ESU's, but due to little information, they are encompassed within one ESU: Xenme3. Other ESU's still ranked as "Xenotoca" melanosoma belong to a spearate not yet described species. 

Habitat: 

  The Black Splitfin lives in ponds, streams and lakes with clear to muddy water (sometimes badly polluted) over substrates of mud, sand, gravel, rocks, boulders and bedrock. There is eiher no vegetation or green algae, Armoracia, Cyperus, Eleocharis, Potamogeton, water hyacinths, Lemna, Nasturtium, Scirpus and Typha. The currents are none to moderate.

Like most of the Goodeids, it prefers depths of less than 1m. It seems to be not very abundant in the habitats as it is rarely observed.

Colouration: 

  Here is the desription of the colouration, given by Fitzsimons in 1972: Against a dark background, adult males may be nearly jet-black, with only the cheek below the eye, and the chin, and the throat and breast region remaining sligthly paler. Immature males or mature males against a light background are uniformly gray along the sides and somewhat darker, with an irregular pattern of small, indistinct spots on the head, nape and back. The chin, breast and abdomen are light gray to grayish white. Depending on the background and size of the fish, the dorsal fin is dusky to black. In large males over 60mm SL the caudal fin may be almost uniformly black. In males approximately 40 to 55mm SL, a concentration of pigment at the base of the principal caudal rays may appear as a poorly defined curved bar or blotch approximately the width of the orbit; in males less than 25mm SL, the basal dark blotch is lacking and the fin appears pale gray to clear. The anal fin is dusky to black but with the membranes of the first six rays, and a narrow marginal band on the membranes of the remaining rays, relatively pigment-free. The paired fins are pale gray to dusky. The dark colouration of males fades considerably in preservative. Females are also dark-bodied but their fins lack the heavy pigmentation seen in males; paired and median fins are palegray to clear. The opercle is pale silvery. The chin, throat and breast are pale gray-white and, in larger females, often lightly speckled. Barring and spotting on the sides of the body and caudal peduncle are conspicuous in immatures and adults against a light background and can be seen even in very large, dark females after preservation. Three to eight scattered vertical bars, varying in length from one to three times an eye diameter, occur on the sides of the body between the pectoral base and the anal origin. In some females they are evenly distributed but in others they may occur in three or more clumps. They are best developed in females 40 to 60mm SL but are less distinct in larger and darker females. An irregular row of five to eight (mostly six) dark spots extends along the midlateral line from the caudal base forward onto the body above the anal origin. Viewed from a distance, the spots often appear as a vague stripe about an eye diameter in width. Speckling is pronounced on the sides and venter of the caudal peduncle but is largely obliterated dorsally by countershading. The venter of courted, sexually responsive females is a brilliant iridescent blue. This colour is transient; it is seen only in the presence of males and quickly fades to an inconspicuous blue- or gray-white when females are disturbed. The venter of immature or sexually unresponsive females is pale white to gray-white.

Biology: 

  Young have been captured late spring, indicating a reproduction from at least March to May.

Diet: 

  The dentition is similar to "Xenotoca" eiseni suggesting an omnivorous feeding behaviour, nevertheless feeding predominantly on aquatic animals and lesser amounts of algae.

Remarks: 

  Fitzsimons (1972) forced crosses between melanosoma and eiseni with producing fertile brood. This is one of rare hybrids among Goodeids, nevertheless a forced one. Presenting each species a conspecific partner, they chose always correctly.

 

   Following recent studies (Domínguez-Domínguez, 2011; Mar-Silva, 2013), the populations from the ríos Ayuqila (Armería basin) and Tuxpán and Tamazula (Coahuayana basin) differ phylogenetically from the rest of populations, so a distinct lineage and clade is recognizable. However, the type of the species came from a tributary of  Río Tamazula, but since 2010, no representative has been seen from the the species in the wild and it may be extinct in the wild.

 

  In contrary to its congeners, the well-known "Xenotoca" eiseni - complexe, the "Xenotoca" melanosoma - complexe is poorly distributed in the hobby, probably because of its dark appearance, but also because of its size.

 

   Fitzsimons described the courtship behaviour of four Goodeid-species in detail, including this one.

Husbandry: 

  Looking on the habitats of "Xenotoca" melansoma, they suggest the species is not in need of a special habitat structure as the locations show no or little vegetation but murky water. Nevertheless, it may prefer dense vegetation and roots (in the aquarium even dense artificial staff) to hide. In the wild, the species occurs in rivers, but always prefering the quiet parts with little current, so it won't be necessary in the aquarium to have strong current. In the aquarium, the fish often hide in the shelter, but courting and impressing males as well as fighting fish of both sexes can often be seen in the open water. Fry is eaten in many cases, rarely not, so it may depend on the quantity and quality of food and on the number of space to hide. When several different stages of juveniles occur, fry is often neglected, so it makes sense to add separate brought up fry to the group with a size of 1.5 or 2cm to provide these stages and get a flock breeding colony.

  The recommended tank size is at least 150 liters, bigger ones are better for sure. Dense vegetation combined with many roots and wood and free space areas for the males to impose and fight make sense. The current should be low.

  In the wild, the species seem to feed as a typical omnivore from small and middle sized invertebrates, aufwuchs, algae, organic matter, smal fish and insects from the surface. "Xenotoca" melanosoma can be fed in the aquarium with food of different sources, composed of different small or middle sized frozen or freeze dried invertebrates (Daphnia, Bloodworms, Artemia), small and middle sized livefood (e.g. Nauplia, Cyclops, Daphnia, Bloodworms. little rainworms, little fish) and good flake food or tablets respectively granulat food. Fish of the "Xenotoca" melanosoma - complexe feed from less vegetarian sources than representatives of the "Xenotoca" eiseni - complexe.

   Concerning water quality, this species is in need of greater water changes (60 - 80% every week), so an automatic water changing system can be helpful. Otherwise, in combination with constant temperatures higher than 24°C, fish may get sick, lose resistance against diseases and burn themselves out. So, mainly for keeping the strain healthy and strong, give the fish a rest during winter time with temperatures lower than 20°C for 2 or 3 months so they stop producing fry. In spring, when the temperature slowly increases, they will start spawning at 20 or 21°C and won't stop until it gets colder again or gets too warm (25°C?).

  This species does very well when is kept in the open from spring to fall, starting when the temperature exceeds 17°C water temperature and cold periods are no longer expected. During the warm summer, reproduction will stop and may occur again in fall. Bring the fish in before the temperature goes below 15°C water temperature and keep them cool for the first days, then slowly raise the temperature but try to stay below 20°C over the winter time.

Locations