Comb scallop

from Wikipedia, the free encyclopedia
Comb scallop
Systematics
Order : Toothpies (Cyprinodontiformes)
Subordination : Cyprinodontoidei
Family : Viviparous toothcarps (Poeciliidae)
Subfamily : Xenodexiinae
Genre : Xenodexia
Type : Comb scallop
Scientific name of the  genus
Xenodexia
Hubbs, 1950
Scientific name of the  species
Xenodexia ctenolepis
Hubbs , 1950

The crested fish ( Xenodexia ctenolepis ) is a freshwater fish that is only known from a few remote rivers in Guatemala . He is a representative of the viviparous toothcarps (Poeciliidae). The Kärpfling differs from the other members of this subfamily in some essential morphological characteristics, which means that it has a special position within the system of viviparous toothcarps.

features

The fish reach a standard length of up to 6 cm, but males are only 2.8 to 4.8 cm fully grown. According to other information, they even grow up to 9 cm. In terms of physique, the Kärpfling is elongated, the head is small and rounded, the fins are relatively small. The eponymous comb scales are unusual for a viviparous tooth carp. The basic color of the body is gray-olive, an elongated black central line decorates the rear half of the body. The fins are dark in color. The scales reflect the light, giving them a metallic sheen. The retina of the eye glows ultramarine blue. The areas between the scales are colored dark, creating a network drawing.

Like all representatives of the viviparous toothcarps, the comb scales also show a sexual dimorphism . The anal fin of sexually mature males is transformed into a mating organ, the gonopodium , which enables the fertilization of the eggs in the female's body. In addition, the male's right pectoral fin is provided with a hook-shaped extension. It is believed that this process supports the reproductive act with the gonopodium, which is also twisted on the right side. No other viviparous toothcar shows such an asymmetry in body structure.

Occurrence and way of life

Xenodexia ctenolepis is so far only known from the Río Negro and its tributaries Río Xalbal and Río Ixcan in the Guatemalan Alta Verapaz department . The sites are described as large, slow to fast flowing jungle streams. The water is clear with temperatures of 22–26 ° C. The river bed of the type locality is 50 m wide and 1–5 m deep. The ground consists of gravel. Occasionally the ground is covered with moss.

Nothing is known about how fish eat in nature. In Aquarium "will pool feed " willingly accepted, even animals are grazing the algae nursery from. They stay in groups and mostly close to the ground.

The fish show superfetation . Eggs of up to five different stages of development ripen simultaneously in the body of the female Xenodexia . The number of stages of development correlates with the size of the females. Females that have recently reached sexual maturity at 39–40 mm in size carry only one litter. On average, between 13 and 22 embryos develop in the mother's body, with an average of 3.5–5 young fish per litter. The embryos are largely supplied with nutrients by the mother, the matrotrophy index (ratio of the mass of the newborn fish to the mass of the unfertilized egg) is between 3.38 and 4.18 and is very high compared to other viviparous toothcarps. The individual eggs are surrounded by follicular tissue in the female's body, which ensures the supply of nutrients. Superfetation in viviparous toothcarps is otherwise known only from dwarf carps ( Heterandria formosa ) and some Poeciliopsis species.

The size of the sexually mature males is remarkably wide. It is believed that it is a polymorphism with regard to age and height at sexual maturity, similar to that of the sword-bearers ( Xiphophorus ).

Systematics

With superfetalation and matrotrophy , the Carpfling shows two characteristics which it was assumed that they developed late in the course of the evolution of the Poeciliinae. However, a phylogenetic study found that Xenodexia ctenolepis is possibly the sister group to all other viviparous toothcarps, including the egg-laying Tomeurus gracilis . One possible explanation would be that matrotrophy and superfetation have developed several times in tribal history, assuming that the Poeciliinae descended from an egg-laying ancestor similar to Tomeurus . On the other hand, the common ancestor could have been viviparous and exhibited both superfetalation and matrotrophy; Properties that in most species were then lost again in the course of development.

Individual evidence

  1. ↑ a b c Donn Eric Rosen, Reeve M. Bailey: The Poeciliid Fishes (Cyprinodontiformes), Their Structure, Zoogeography and Systematics. In: Bulletin of the American Museum of Natural History 126, New York, 1963, pp. 141-143.
  2. ↑ a b c d e f g David Redzick u. a .: Life history of Xenodexia ctenolepis : implications for life history evolution in the family Poeciliidae. In: Biological Journal of the Linnean Society 92, 2007, pp. 77-85. doi : 10.1111 / j.1095-8312.2007.00869.x
  3. ↑ a b c Michael Kämper: Xenodexia ctenolepis - remarks about an unusual aquarium fish. In: DGLZ Rundschau 36, No. 1, 2009, ISSN  0938-7455 , pp. 3-4.
  4. ↑ a b Manfred K. Meyer, Lothar Wischnath, Wolfgang Foerster: Livebearers Zierfische: Species of the world. Mergus Verlag für Natur- und Heimtierkunde Baensch, Melle 1985, ISBN 3-88244-006-6 , pp. 356-358.
  5. ^ A b Carl Leavitt Hubbs: Studies of cyprinodont fishes. XX. A new subfamily from Guatemala, with ctenoid scales and a unilateral pectoral clasper. In: Miscellaneous Publications. Museum of Zoology, University of Michigan 78, University of Michigan Press, Ann Arbor, 1950.
  6. ↑ Tomas Hrbek u. a .: Molecular phylogeny of the Poeciliidae (Teleostei, Cyprinodontiformes): biogeographic and life-history implications. In: Molecular Phylogenetics and Evolution 43, pp. 986-998. doi : 10.1016 / j.ympev.2006.06.009

Web links