African bonebreaker

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African bonebreaker
Heterotis niloticus The fishes of the Nile.jpg

African bonesweed ( Heterotis niloticus )

Systematics
Subclass : Real bony fish (Teleostei)
Overcohort : Osteoglossomorpha (Osteoglossomorpha)
Order : Bony tongues (Osteoglossiformes)
Family : Arapaimidae
Genre : Heterotis
Type : African bonebreaker
Scientific name of the  genus
Heterotis
Rüppell , 1828
Scientific name of the  species
Heterotis niloticus
( Cuvier , 1829)
Heterotis niloticus , prepared specimen in the Museum of Toulouse

The African bone- winged fish ( Heterotis niloticus ) is a bony fish from the order of the bone-winged fish . In his vast African homeland he has hundreds of vernacular names , none of which has gained greater prominence, so that the French call him the "nameless" ( poisson-sans-nom ). It becomes just over 1 m long and weighs 11 kg, whereby males and females can hardly be distinguished externally. (A special feature is that both have only one left gonad !) In contrast to its closest relatives, it is not a predatory fish, but lives almost exclusively on fine plankton and detritus - like the kissing gourami ( Helostoma ). It goes without saying that such a fish has the potential to serve as a pond fish for human consumption - thanks to air breathing , it is also insensitive to oxygen deficits in the water. Otherwise it lives in the open water of larger bodies of water, but also often near the banks and the ground. Much of its biology is still uncertain.

Exterior

Of all Knochenzünglern has Heterotis nor the "most normal" fish shape. The caudal fin is small and rounded. The tail stalk is very short. The color is yellowish to dark gray-brown. Young fish sometimes have dark bands and dark spots on the scales at the bases of the unpaired fins. The oval scales are large (35–40 along the slightly downward sloping side line) and sculpted in a worm shape (which is rarely the case with Teleostei ). The large eyes sit just behind the corners of the mouth (far in front and far to the side). Since the maxillae swing forward when the mouth is opened, the small mouth soon becomes round (actually square - but it cannot be stretched out), just like the carp . It is surrounded all around by long, conical, but not very pointed, small teeth in a row, which are also used to scrape off growth. The mouth is a little under, its edge thickened. The head lags behind (as usual) as it grows - old individuals are therefore quite small-headed. The gill cover (sometimes with a black spot) has a very wide skin border on the side, so the gill gap is short, it only extends to the base of the deeply drawn-in pectoral fin.

construction

In 1854, Joseph Hyrtl provided an anatomy of the fish that is still readable. The cranial cover bones are also heavily sculpted. Because of microphagia, there is a dense gill trap with 21–76 Branchoctenia on Epibranchiale I and 33–98 on Ceratobranchiale I (i.e. the number increases significantly with age) - correspondingly less on arcs II to IV. The “internal bite” can only be insignificant in this osteoglossiform: Basihyale and Parasphenoid are just rough with small teeth; The pharyngeal dentition is just as insignificant . The epibranchial organ is to be discussed separately. As with other detritophages ( Dorosoma cepedianum , Mugil cephalus ) there is a separate gizzard in which diatoms or macrophyte seeds are ground up using sand . The midgut is long; At its beginning two very long porter or pyloric tubes open out . The swim bladder emanates from the pharynx without a connecting duct , is chambered, broadly fused with the kidney, and continues into the hemal canal of the (approx. 43) caudal vertebrae. It is obligatory (?) For air breathing (which Hyrtl still doubts - it is certain in the similarly built Arapaima . The opinion that is often still expressed that heterotis has branchial air respiratory organs is therefore by no means true).

The epibranchial organ

Dorsally (on both sides of the body) behind the fourth gill arch, inside of the gill cover, a crevice opens into the cartilaginous and muscular epibranchial organ, which initially curves forward in an arched conical shape and then merges into a spiral that has the shape of a common or ramshorn snail (namely Planorbis carinatus ) shows. The cavity of the organ is initially lined by the pharynx with small branchiospins and numerous taste buds .

An epibranchial organ is a facility of several primitive Teleosteer families, previously grouped as herring-like ("Clupeacei") families, with plankton or microbenthos food. His skeletal base could be the cartilaginous called Epibranchiale the fifth gill arch that over a century ago in Characinen ( tetras was discovered) (M. sawdust 1884). The organ produces mucus, possibly under the influence of the taste organs (only when certain algae predominate - whereby the branchioctenia may first unlock them?). A similar function can be ascribed to the palate pad of the Cyprinidae (in front of the chewing plate - these fish therefore already have "pharyngeal jaws", the "old" herring-like ones up to Gonorynchus do not yet!). (See also Plecoglossus altivelis , algae eater with mucus-producing tongue folds.) In eutrophic waters, heterotis can feed itself solely through normal breathing movements.

The rolled up part of this “multi-purpose organ” is innervated “lengthways” by a strikingly thick vagus branch. But the function of this striking structure is still not clear.

Hyrtl admits: If this snail is an additional respiratory organ, only one of subordinate importance, because the blood supply is too weak. The shape is irrelevant - what counts is just the increase in surface area (which is of course not true: a snail is unsuitable for air or water exchange). But Hyrtl also accepts arguments in favor of a sensory function (taste or even hearing?) - and hearing is of course preferable in view of the snail shape. ' heterotis ' means “(animal) with special ears” (because its discoverer Rüppell already interpreted the snail in this way); Hyrtl, however, wants - despite the above considerations - at a time when scientific names should also be carriers of meaning, to have them changed to Helicobranchus (i.e. snail gill - since Heterobranchus was already preoccupied with a catfish ). It will be interesting to see what other sensory physiology will bring out here.

Way of life

Smaller specimens are found in loose flocks that are said to be gasping at the same time. The diet consists of algae, zooplankton (e.g. water fleas ), growth, detritus (e.g. decaying macrophyte tissue including bacteria and fungi), small fruits and seeds (also blown into them, from land plants) and meiobenthos (it digs like a carp The stomach and intestines contain enzymes for breaking down vegetable carbohydrates) - but it also digests worms, insect larvae, small snails and mussels and the like. Ä .; large specimens (10-12 years old) sometimes even “prey” on small fish.

Heterotis becomes sexually mature with a length of approx. 40 cm (2–2.5 years old). In the spawning season at the beginning of the rainy season - it gets a little darker and males and females show a bonding ritual - a kind of small pond ("nest", up to 1 m in diameter) is created in macrophyte populations ("reeds") Teeth removed to the outside, the bottom deepened or piled up like a wall on the outside (with an opening for swimming through). Hundreds (?) Thousands of eggs are laid and guarded. The larvae hatch after about three days, initially have external gills (threads: Budgett 1896) and are further guarded (“guided”?) By the male until they disperse into the surrounding vegetation. The mortality is initially very high. Spawning can be done several times per season. The “nest” is tempting for people living subsistently and therefore easily led to local population threats (otherwise it is quite shy).

distribution

The distribution area is south of the Sahel zone , from Senegal to Lake Turkana . There it occurs in lakes (e.g. Lake Chad ), rivers, swamps (e.g. in Sudan: Sudd ) and ponds. In places it even penetrates brackish water ( mangrove , e.g. in Nigeria , Togo ) and salt lakes (Turkana or Rudolf lakes) at 26–30 ° C. This area has already been expanded by man (e.g. into the Congo Basin ) - so that the fish has now also been found in Madagascar (since 1963) . (Since he breathes air, he can withstand unfavorable transport conditions for a long time.) Locally, he can harass more useful species (such as tilapia ). (So ​​it seems that it is not too valued as a food fish , especially since it has bones.) Due to its diet, it is also uninteresting and unsuitable for aquaristics.

relationship

Since the bones are phylogenetically very old, the species of which had evolutionary times millions of years, it is not surprising that, despite being monotyped , Heterotidae were soon placed in their own family (Heterotidae - correctly should have been "Heterotididae" - hence a subfamily today too Heterotidinae). Now the prevailing opinion is that families should express relationships. Therefore one counts Heterotis with Arapaima (from S-America), despite considerable differences, in the family Arapaimidae . C. Ferraris claims of the latter that it should be called "Arapaimatidae" - because the vernacular name arapaima is not feminine, but neutral. By the way, in the 19th century the heterotis was long known as Clupisudis .

Remarks

  1. ↑ according to Hyrtl, who, however, himself indicates doubts. The organ in the hemal canal could also be part of the kidney or a gonad.
  2. ↑ due to low blood supply; but that's enough for fishing (Hyrtl was a medic)!
  3. ↑ or, in other words: this “epibranchial V” of the tetra could be a rudiment of the epibranchial organ.
  4. ↑ According to Bauchot et al. the cavity of the organ consists of two parallel channels, separated by a membrane. The outer half carries water against the apex of the snail, the inner half carries the mucus produced by the membrane with sticky algae to the esophagus. R. Bauchot, J.-M. Ridet, and M. Diagne (1993): The epibranchial organ, its innervation and its probable functioning in Heterotis niloticus (Pisces, Teleostei, Osteoglossidae) .- Environmental Biology of Fishes 37: 207-215.
  5. ↑ Due to the large "taste center" (it is also snail-shaped!) In the posterior brain, similar to cyprinids, these fish achieve a high degree of encephalization .
  6. ↑ from the female? - less believable.

Individual evidence

  1. ^ Joseph Hyrtl: Contribution to the anatomy of Heterotis Ehrenbergii C. Vienna 1854. From: Sitzg.-Ber. d. emperor. Akad. D. Scientific, mathematic-natural Classe 12/13: 430-445 (also in the memorandum of 1855)
  2. ↑ skull s. Gregory 1933: http://www.archive.org/stream/fishskullsstudyo00gregrich#page/164/mode/2up/search/heterotis
  3. ↑ Mark R. Braford Jr. (1986): De gustibus non est disputandum : A spiral center for taste in the brain of the teleost fish, Heterotis niloticus .- Science 232. pp. 489-491.
  4. ↑ https://www.youtube.com/watch?v=_8ZDOFezctI
  5. ↑ AA Ugwumba (1993): Carbohydrases in the digestive tract of the African bony-tongue Heterotis niloticus (Pisces: Osteoglossidae). Hydrobiologia 257: 95-100.
  6. ^ CJ Ferraris (2003): Family Arapaimatidae. In: Check List of the Freshwater Fishes of South and Central America. Pp. 582-588. (RE Reis, SO Kullander & CJ Ferraris (eds.). Porto Alegre, Brazil: EDIPUCRS.)

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