Salamander fish
| Salamander fish | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the order | ||||||||||||
| Lepidogalaxiiformes | ||||||||||||
| Betancur-R. , Broughton, Wiley, et al., 2013 | ||||||||||||
| Scientific name of the family | ||||||||||||
| Lepidogalaxiidae | ||||||||||||
| Rosen , 1974 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Lepidogalaxias | ||||||||||||
| Mees , 1961 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Lepidogalaxias salamandroides | ||||||||||||
| Mees, 1961 |
The salamander fish ( Lepidogalaxias salamandroides ) is a small freshwater fish that was described in 1961 from waters in southwest Australia (between the Blackwood River and Walpole ), where it occurs endemically in periodically drying water holes. It is the only species that represents the sub-cohort Lepidogalaxii , which was established especially for it and whose origins go back over 90 million years.
description
The color of Lepidogalaxias salamandroides is olive-green or -brown, mottled dark; the ventral side is white-silvery to pink in color. The eyes are relatively large and reddish. Its shape resembles that of the loaches : elongated cylindrical, the length corresponds to about twelve times the width. This fish only reaches 7.5 cm in length, the males remain smaller and barely reach 5 cm. The males are generally a little darker in color and have a unique anal fin covered with scales. The side line is clear (marked in the form of a band in males) and runs over about 65 thin embedded scales. Dandruff is absent on the back, stomach and head. The caudal fin looks, as no caudal stalk is recognizable, as if glued to it. What is striking is the low number of rays in all the fins, the rays are segmented but undivided.
Fin formula : D 5-7 (short and high), A 10-12 (low), P 10-12 (long), V 5, C 12-14 (round or slightly pointed).
The fins are faintly pigmented along the rays. The mostly steeply erect dorsal fin stands just after the middle of the animal's total length and just in front of the anal fin. The fish has 43–47 vertebrae (for comparison: in Galaxiinae 37–66).
Because of this, and because some organs appear simplified internally, Lepidogalaxias are sometimes counted among the neotene animal forms, i.e. those that become sexually mature as larvae (other Osmeriformes for which this applies are the Salangidae , which do not occur around or in Australia ). However, this view is of little help. Neither smallness nor short life are sufficient reasons for neoteny, and others are unclear. Incidentally, females can live to be five years old, so they are not particularly short-lived.
The snout is short and blunt, but the mouth is deeply split and well toothed, especially on the premaxillary and dentals. The short maxillary is exposed in the skin of the mouth rim and is edentulous. The palatine (a row of teeth) opposite the dentate basihyale ("tongue bite") and (weakly) the vomer (two teeth) are well-toothed . The gill cover is only deeply ossified at the edge and so thin that the red gills shine through. There are no pyloric tubes on the intestine (he shares that and the "tongue bite" with pike , see below).
The "neck" consists of a purely chordal connection between the occiput and the first vertebra (when at rest it is broadly adjacent to a joint on the basioccipital and exoccipital), but the mobility of the following three is still very little restricted by joints. Incidentally, this "neck" is necessarily behind the shoulder girdle , not in front of it as in terrestrial vertebrates .
behavior
The German-speaking name salamander fish was chosen based on the scientific species name salamandroides . The name “lizard fish” would suit the behavior of the species better - but this name is already given for the Synodontidae . The lizard-like aspect of Lepidogalaxias lies in the movements of the head, which are unique to fish and which also do not occur in salamanders because their necks are not as flexible as those of lizards . Lepidogalaxias can bend its head to the side by almost 90 °, for example to observe a prey next to it.
McDowell and Pusey reported in 1983 that the species lacked the eye muscles . However, Collin and Collin demonstrated in 1996 that there were six extraocular muscles that allow the eye to move freely under the glasses . The salamander fish has very large eyes; they are the main sensory organs for preying. Big eyes are in the boggy - d. H. transparent, but dark - water is an advantage (see also Hyperprosopon argenteum ).
Distribution and ecology
The salamander fish lives in smaller, shallow ponds and ponds on the edge of the Australian shield (between Blackwood R. and Kent River, partly in the small national parks Shannon and D'Entrecasteaux around Northcliffe, 350 km south of Perth ) on primary rock sand that is very is low in nutrients. The consequences are sometimes extremely low pH values (3.0 to 6.5) and very low biological productivity . These waters resemble our bog eyes . In the southern summer they usually dry out due to a lack of precipitation. In winter (June – August; rainy season) connect z. T. brooks from the foliage of the surrounding vegetation (esp. Eucalyptus ) by humic substances u. Ä. brown ("tea-colored") pond in the water. The water temperatures fluctuate strongly due to the insolation (15-30 ° C). Here young and old animals of Lepidogalaxias live mainly on insect larvae and small crustaceans. The benthic fish usually lurks motionless, erect on its pectoral fins. If it perceives movement in its surroundings, it swims jerkily closer, aligns its head and quickly grabs the prey - it is very reminiscent of a lizard.
The breeding season coincides with heavy rains between late May and August. The gender ratio is approx. 1: 1. Mating falls in early spring (June) - the salamander fish has internal egg fertilization. But there is no courtship or other sex foreplay. Similar to the (unrelated) surf perch (Embiotocidae), the anal fin of the male has a basal scale covering that, together with a sticky secretion, helps to press the sexual orifices of both partners so tightly that the semen can be safely transferred. A few days later, the female lays around 120 eggs a little more than a millimeter in diameter. The purpose of internal fertilization is probably to waste as little protein as possible in the nutrient-poor biotope and to develop the eggs as early as possible so that there is enough time for the larvae and young fish (which feed on small crustaceans and insect larvae) to grow before the dry season comes. When hatching, the larvae are 5.5 mm long and ready to eat. The growth is rapid; the juvenile fish must be 25 mm long in order to survive the "overwintering" ( estivation ) - albeit often with losses of up to 75%. It is important to have a fat reserve (as is the case with winter sleepers - but not common with fish), which also supplies water when consumed.
When the water in the pond runs dry (December, January), the fish penetrate different depths into the wet sand, where they take a U-shaped posture. Your skin (and especially the cornea of the eye) shows special adaptations to the stresses that arise. In contrast to the lungfish , which also bury themselves for aesthetic purposes (although not the Australian species ), they have no respiratory adaptation to it; an excretory but the synthesis of urea . At first it was also held Lepidogalaxias for air-breathing , but is swim bladder reduced in the demersal and for that very inappropriate. It also has no adaptation to oxygen depletion in residential water (i.e. this does not matter). However, skin respiration is important for survival in dry periods, as oxygen and carbon dioxide are exchanged through damp skin. The animals do not eat while they are buried.
Larger fish can follow the sinking water table to a depth of 60 cm, while animals that are too small dry up if the rain does not rain for too long. But if he comes in time (April), everyone is active again very quickly ( Tim Berra , to whom we owe most of the observations, had a dry pond filled with a tank truck: all the fish came out of the sand within 10 minutes!) And are aged Sexually mature for 1 year (the females are then on average 43 mm long, the males 39 mm). If a vintage should be completely canceled due to unfavorable weather conditions, older fish still live (buried deep) and regenerate the population. Annuals and older animals still make up an average of 56% of the total population, but many die after spawning, all of the males; few do not become sexually mature until they are two years old or even older. But only very few (females) get older (3 years and more).
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Phylogenetic position of
Lepidogalaxias salamandroides
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Systematics
After the discovery, the salamander fish was assumed to be related to the Galaxiidae and Retropinnidae (both Australian; Galaxiidae are however scaly and without a "tongue bite", Retropinnidae with a "tongue bite", smelt- like ), assigned to the smelt- like (Osmeriformes), although z. B. no adipose fin is present. Incidentally, Joseph S. Nelson (2006) only grants the salamander fish its own subfamily of the galaxids. Rosen's assignment to the Esociformes (pike) was based e.g. Partly on erroneous assumptions and plesiomorphies . With Robert Williams Lepidogalaxias is in a sister group relationship to the Galaxioids, as which he combines Galaxiidae and Aplochitonidae (otherwise: -inae). Jun Li et al . Come to a comparison of Lepidogalaxias with all other Euteleosteomorpha , a view that Ricardo Betancur-R. and colleagues take over in their latest revision of the bony fish systematics and set up their own sub-cohort, the Lepidogalaxii, for Lepidogalaxias .
protection
Lepidogalaxias salamandroides lives z. Sometimes in protected areas, but indirectly through wood extraction, slash and burn, dam construction, introduced species (e.g. cichlids) and the like. a. potentially threatened due to precarious living conditions and small-scale endemism . Trayler et al. therefore call for more specific measures to protect the habitats of the Warren Bioregion.
literature
- Berra, Tim M. 1995. Lepidogalaxiidae. Lepidogalaxias salamandroides. The Salamanderfish of Western Australia. Version 01 January 1995. in The Tree of Life Web Project
- Joseph S. Nelson: Fishes of the World , John Wiley & Sons, 2006, ISBN 0-471-25031-7
Individual evidence
- ^ Gerlof Fokko Mees: Description of a new fish of the family Galaxiidae from Western Australia. JR Soc. West. Austr., 44, pp. 33–41, 1961 (first description)
- ↑ a b c d e f g G. Allen, S. Midgley, M. Allen: Field Guide to the Freshwater Fishes of Australia . 2nd Edition. Western Australian Museum, Perth 2003, ISBN 0-7307-5486-3 , pp. 117-119 .
- ^ A b c Tim M. Berra: Freshwater Fish Distribution. University of Chicago Press, 2007, ISBN 978-0226044422 , pp. 263-266.
- ^ Adalberto Luis Val, Vera Maria F. De Almeida-Val, David J. Randall: The Physiology of Tropical Fishes: 21 (Fish Physiology). Academic Press, 2003, ISBN 978-0123504456 , pp. 69-70.
- ↑ a b R. Betancur-R., E. Wiley, N. Bailly, A. Acero, M. Miya, G. Lecointre, G. Ortí: Phylogenetic Classification of Bony Fishes - Version 4 (2016)
- ↑ Don E. Rosen (1974): Phylogeny and zoogeography of salmoniform fishes and relationships of Lepidogalaxias salamandroides . Bull. Amer. Mus. Nature. Hist. 153: 267-325.
- ^ Robert RG Williams (1997): Bones and muscles of the suspensorium in the Galaxioids and Lepidogalaxias salamandroides (Teleostei: Osmeriformes) and their phylogenetic significance. Records of the Australian Museum 49: 139-166.
- ↑ Jun Li, Rong Xia, RM McDowall, J. Andrés López, Guangchun Lei, Cuizhang Fu, (2010): Phylogenetic position of the enigmatic Lepidogalaxias salamandroides with comment on the orders of lower euteleostean fishes. Molecular Phylogenetics and Evolution, Volume 57, Issue 2, November 2010, pages 932-936, doi: 10.1016 / j.ympev.2010.07.016
- ↑ KM Trayler, JA Davis, P. Horwitz, and D. Morgan (1996): Aquatic fauna of the Warren bioregion, south-west Western Australia: Does reservation guarantee preservation? - JR Soc. West. Austr. 79: 281-291.
Web links
- Salamander fish on Fishbase.org (English)
- Berra, Tim M. 1995. Lepidogalaxiidae. Lepidogalaxias salamandroides . The Salamanderfish of Western Australia. in The Tree of Life Web Project .
- Lepidogalaxias salamandroides inthe IUCN Red List of Threatened Species 2010.4. Posted by: R. Wager, 1996. Retrieved February 22, 2011.