Hatchet tetra

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Hatchet tetra
Carnegiella marthae

Carnegiella marthae

Systematics
Overcohort : Clupeocephala
Cohort : Otomorpha
Sub-cohort : Ostariophysi
Otophysa
Order : Tetras (Characiformes)
Family : Hatchet tetra
Scientific name
Gasteropelecidae
Bleeker , 1859

Hax-bellied tetra (Gasteropelecidae) are a family from the order of the tetra-like species with currently nine species in three genera that are native to South and Central America. The striking body shape, reminiscent of a hatchet, motivated the scientific naming ( Greek gaster "belly", pelekis "hatchet") as well as the popular German name. Some of the species are popular aquarium fish .

distribution

The distribution area of ​​the hatchet tetra includes all states of the South American continent (except Chile ) and Panama . In Panama, the northern border of the range, only the spotted hatchetfish ( Gasteropelecus maculatus ) occurs. All other species of the hatchet-bellied tetra inhabit waters of northern and central South America up to the Río de la Plata in Argentina .

features

The particular body shape of the hatchet-bellied tetra represents a specialization of life on the surface of the water. The back profile is almost horizontal, while the chest and belly lines are strongly arched and the mouth above . In relation to their body size, they have an enlarged shoulder girdle with strong muscles of the wing-like pectoral fins , which make up up to 25% of their body weight. In contrast to the species of the other two genera, species of the genus Carnegiella have no adipose fin . Depending on the species, hatchet-bellied tetra reach a body length between approx. 30 and 90 mm.

Hatchet tetra are able to shoot above the surface of the water and “fly” straight through the air for several meters. They make a whirring noise. Since the movement through the air is ascribed to the active propulsion by flapping the pectoral fins, they are often referred to as the only true flying fish, in contrast to the marine flying fish (Exocoetidae), which only glide through with the help of their wing-like pectoral fins move the air. The meter-wide jump out of the water is probably not used for hunting or for grabbing the prey, but is only an escape behavior in the event of threats from the water, such as attacks by predatory fish.

Whether the hatchet tetra really have an active ability to fly is a matter of dispute among experts. While SH Weitzman, according to his own statements, was only able to observe the flight indirectly and attributed the whirring noise to the beating of the pectoral fins as a plausible explanation, high-speed recordings and movement analyzes in the laboratory could not confirm this. Rather, the pectoral fins were only beaten against the surface of the water in the starting phase, while at the same time the tail fin provided the propulsion until the fish could leave the water. In the actual flight phase, the pectoral fins were not used, only the caudal fin that produced the whirring sound. The sequence of movements observed in the laboratory does not seem to be able to explain the longer distances that are reached in nature.

Way of life

Hax-bellied tetra live in running waters such as streams, rivers and streams as well as in still waters such as ponds, lakes and temporarily flooded floodplains. They prefer to stay close to the water surface, in areas where it is largely free of plants. In order to escape predators such as the pike tetra , they remain almost without exception in the immediate vicinity of water zones that offer protection, which, depending on the type of water and the degree of shade, are dominated by dense aquatic plants, swamp or land plants reaching into the water or heavily branched dead wood collections.

The waters in which hatchet-bellied tetra live are mostly very soft, low in minerals and acidic. Often the total and carbonate hardness is below the detection limit at pH values below 5. More rarely, populations are found in medium-hard to hard and slightly alkaline water. The glass hatchetfish ( Carnegiella myersi ), for example, was caught in very soft and acidic waters as well as in waters with a total and carbonate hardness of around 15 ° dH and a pH value of up to 7.7. Depending on the species, biotope and season, the water temperature can be below 20 ° C to over 30 ° C.

Hax-bellied tetra live sociable in larger groups , sometimes in schools. They mainly hunt small insects and spiders that have fallen on the water surface , but also insect larvae living near the water surface.

Systematics

According to the revision by Stanley H. Weitzman and Lisa Palmer in 2003, nine species are currently described in three genera.

Since there are clear differences in the coloration of different populations of the same species, Weitzman and Palmer do not rule out the possibility that there are still undescribed species. In mid-2013 it was found that the marbled hatchet-bellied fish is a shoal of very closely related and externally hardly or indistinguishable species. The smaller black- winged hatchet-bellied fish lies phylogenetically within the C. strigata school of species and is more closely related to the C. strigata population found in north-western Brazil near Barcelos than this z. B. with the C. strigata population found in the western state of Acre . This makes C. strigata a paraphyletic group that will have to be divided into several species in the future. The genus Gasteropelecus is also paraphyletic with Gasteropelecus maculatus as a basal sister species of all other hatchet-bellied fish and Gasteropelecus sternicla as a sister group to the genus Carnegiella . The sister group of the hatchet tetras is the family Bryconidae with the two subfamilies Bryconinae and Salmininae , relatively large fish with a trout-like appearance.

swell

literature

Individual evidence

  1. ↑ a b c S. H. Weitzman, L. Palmer: Family Gasteropelecidae (freshwater Hatchetfishes). In: RE Reis, SO Kullander, CJ Ferraris Jr. (Eds.): Check List of the Freshwater Fishes of South and Central America. Edipucrs Verlag, 2003, ISBN 85-7430-361-5 , pp. 101-103.
  2. ^ A b c Tim M. Berra: Freshwater Fish Distribution. The University of Chicago Press, 2007, ISBN 978-0-226-04442-2 , pp. 130-132.
  3. ^ Wolfgang Staeck: Tetra from South America. Verlag Dähne, 2008, ISBN 978-3-935175-41-8 , p. 75.
  4. ^ R. Förster, J. D'Haese, H. Graeve: Morphological investigations on the "flight apparatus" of hatchet-bellied tetras. IV Symposium on the Ecology and Systematics of Fish and II. Conference of the Society for Ichthyology. Program and short version of the contributions. Verlag Natur und Wissenschaft: 24 quoted by Wolfgang Staeck: Salmler from South America. Verlag Dähne, 2008, ISBN 978-3-935175-41-8 , p. 76.
  5. ↑ Kelly T. Abe, Tatiane C. Mariguela, Gleisy S. Avelino, Ricardo MC Castro, Claudio Oliveira: Multilocus molecular phylogeny of Gasteropelecidae (Ostariophysi: Characiformes) reveals the existence of an unsuspected diversity. In: Molecular Phylogenetics and Evolution. July 2013, doi: 10.1016 / j.ympev.2013.07.005

Web links

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