African arowana

African osteoglossid ( Heterotis niloticus )

The African osteoglossid ( Heterotis niloticus ) has hundreds, in its extensive African homeland vernacular names, but of which no greater notoriety has acquired, so that the French call him the " Nameless " ( poisson -sans- nom ). He is just over 1 m in length and 11 kg in weight, with males and females are almost indistinguishable externally. ( A special feature is that both have only one left gonad! ) Unlike its closest relatives he is not a predator, but lives almost exclusively of fine plankton and detritus - such as the kissing gourami ( Helostoma ). It is understood that such a fish has the potential to serve as a pond fish for human consumption - thanks to air breathing he's insensitive to oxygen deficiency in the water. Otherwise, he lives in the open water of larger waters, but also often in riparian and ground nearby. Much of its biology is still uncertain.

Appearance

Of all Knochenzünglern Heterotis still has the " most normal " fish shape. The caudal fin is small and rounded. The caudal peduncle is very short. The color is yellowish to dark gray-brown. Juveniles sometimes have dark bands and on the scales at the bases of Unpaarflossen dark spots. The oval scales are large (35-40 along the slightly downward curved side line) and vermiform sculpted (what else to the extent hardly occurs in Teleostei ). The large eyes are set equal to ( far front and far side ) behind the mouth. Since the maxillae Preshoot the mouth opening, the little mouth like a carp is soon around (actually square - but it can not be paid in advance ). It is a long round of tapered, but not very sharp little teeth surrounded in a row, probably also serve the scraping of nursery. The mouth is slightly inferior, its margin thickened. The head remains ( as usual ) back in growth - old individuals are therefore quite kleinköpfig. The gill cover ( sometimes with black spot ) has laterally a very broad cutaneous rim, the gill slit is so short, it comes down only to the base of deeply articulated pectoral fin.

Fins formula: D 32-37, A 34-39, 11-12 P, V 6, C 15 - 7 thin Branchiostegalradien - 66-69 vertebrae..

Construction

Joseph Hyrtl delivered in 1854 a still readable anatomy of the fish .. The Skull Deck bone are strongly sculptured -. Mikrophagie Because there is a dense gills Reuse with 21-76 Branchoctenien on the Epibranchiale I and 33-98 on the Ceratobranchiale I ( ie, the number increases with age very clearly ) - on the sheets II to IV correspondingly less. The "inner bite" may be insignificant in this Osteoglossiformen: Basihyale and parasphenoid are merely rough of small teeth; as insignificant is the Pharyngealia - dentition. On the Epibranchialorgan shall address separately. As with other Detritophagen ( Dorosoma cepedianum, Mugil cephalus ) is a separate gizzards, are in the pulverized by sand about diatoms or macrophytes seeds. The midgut is long; at its beginning merge two very long porter or Pylorusschläuche. The swim bladder is without connecting passage from the pharynx out, is chambered, grown wide with the kidney, and continues in the Hämalkanal of (about 43 ) caudal vertebrae. It serves the obligatory air breathing (? ) (Which Hyrtl still doubted - it's backed up with the similarly constructed Arapaima The often expressed opinion, Heterotis would branchiale air respiratory system, ie it makes no means. ).

The Epibranchialorgan

Dorsal opens ( on both sides of the body ) after the fourth branchial arch, inside the gill cover, a column in the cartilaginous and muscular Epibranchialorgan, the first arched conical bends forward and then goes into a spiral that completely the shape of a cup or horn snail (namely, Planorbis carinatus ) shows. The cavity of the organ is initially lined by pharyngeal mucosa with small Branchiospinen and numerous taste buds.

A Epibranchialorgan is a means of several earlier than herring -like ( " Clupeacei " ) summary primitive teleosts families with plankton and microbes Thos food. His skeleton base could be the cartilaginous called Epibranchiale of the fifth branchial arch, which over a hundred years ago Characinen ( characins ) was discovered (M. sawdust 1884). The body produces mucus, possibly under the influence of taste organs (only for the prevalence of certain algae - the only catch Branchioctenien like this - ). A similar function can be the palate cushion the Cyprinidae (before the gummy plate - so these fish have " pharyngeal jaws ", the "old" herring -like to Gonorynchus not yet! ) Attribute. ( See also Plecoglossus altivelis, algae eater with slime-producing tongue folds. ) - In eutrophic waters Heterotis can therefore nourished solely by means of normal respiratory movements.

Rolled portion of this " multi- organ " is innervated by an unusually thick vagal branch " longitudinal". But the function of this striking structure is still not released.

Hyrtl admits: Should this screw be an additional respiratory organ, so only one of minor importance, because the blood supply is too weak. The form is irrelevant - what counts, is merely the increase in surface area ( which is not true: a snail is so unsuitable for air or water exchange). But Hyrtl can also arguments in favor of a sensory function apply (taste or even heard? ) - And then, indeed, is the hearing to be preferred in view of the snail form. ' Heterotis ' means " ( animal ) with special ears" ( because even its discoverer Rüppell the screw as indicated ); Know amended, in a time when scientific names should be bearers of meaning, in this " Helicobranchus " (ie Schneckenkiemer - - because Heterobranchus was already präökkupiert with a catfish ) Hyrtl but will - in spite of the listed considerations. It will be interesting what the sensory physiology still brings out here.

Way of life

Smaller specimens come together to loose flocks that supposedly breath of fresh air at once. The diet consists of algae, zooplankton (eg cladocerans ), nursery, detritus (eg decaying Makrophytengewebe, bacteria and fungi ), small fruits and seeds ( also blown into it from land plants ) and meiobenthos ( green he punched like a carp and seiht mud through the stomach and intestine enzymes are found for hydrolysis of vegetable carbs ) - but he also digested worms, insect larvae, small snails and clams and the like. .; large individuals (10-12 years old ) " capture " sometimes even small fish.

Sexual maturity Heterotis with about 40 cm in length ( 2-2.5 years old ). In the spawning period at the beginning of the rainy season - it is something darker and males and females show a bonding ritual - is in macrophytes ( " reed " ) a kind of small pond ( "nest", up to 1 m in diameter) created: plants are sprayed with the teeth removed to the outside, deepens the base or the outside like a wall piled up ( with an opening for swimming). Hundred (? ) Thousands of eggs are laid and guarded. The larvae hatch in about three days, in the beginning have external gills ( filaments: Budgett, 1896) and are further from the male guards ( " out "? ) Until they disperse into the surrounding lush vegetation. The mortality rate is initially very high. Spawning can take place several times per season. The "nest" is tempting for subsistent living people, and causes locally easy to population threats (otherwise he is quite shy ).

Dissemination

The distribution area is located south of the Sahel, from Senegal to Lake Turkana. There he comes in lakes (eg Lake Chad ), rivers, swamps: prior and ponds (eg in Sudan Sudd ). In places, it penetrates even in brackish water ( mangrove, for example, in Nigeria, Togo) and salt lakes ( Turkana or Lake Rudolf ) at 26-30 ° C. From the people of this area has been expanded ( eg to the Congo Basin ) - so that the fish are now about also occurs on Madagascar (since 1963). ( He breathes air, he also holds unfavorable transport conditions for long periods of good. ) Local he can harass more useful species (eg tilapia ). ( So it seems that it is not too valued as a food fish, especially since he has bones. ) Due to his diet, he is uninteresting and also unsuitable for the aquarium.

Relationship

Since the osteoglossid are a phylogenetically very old order whose species had many millions of years of evolution time, it is not surprising if one Heterotis despite monotype soon turned into its own family ( Heterotidae - would correctly have to be even " Heterotididae " - hence today subfamily Heterotidinae ). Now outweighs the opinion Families should bring affinities expressed. Therefore, you count Heterotis with Arapaima ( from S America ), despite considerable differences in the Arapaimidae family. C. Ferraris claimed by the latter, they would have to " Arapaimatidae " hot - because the Vernakularname arapaima is not feminine, but neutral in the 19th century was called the Heterotis long way " Clupisudis ".

Observations and literature

Weblink

• African osteoglossid on Fishbase.org (English)
• Heterotis niloticus in the Red List of Threatened Species IUCN 2013.2. Posted by: Akinyi, E., Azeroual, A., Entsua -Mensah, M., Getahun, A., Laleye, P. & Moelants, T., 2009, Accessed on 12 January 2014.

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