Surgeon fish
| Surgeon fish | ||||||||||||
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Arabian surgeonfish ( Acanthurus sohal ) |
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| Acanthuridae | ||||||||||||
| Rafinesque , 1810 | ||||||||||||
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The surgeon fish (Acanthuridae), also called sea bath or surgeon fish , form a family in the order of the surgeon fish-like (Acanthuriformes), which includes two subfamilies , six genera and over 80 species . The surgeonfish's closest relatives include the halterfish and the dianafish .
The name doctor fish is derived from the "scalpels" or horn-like blades that these fish carry in front of the root of their tail and that they can use as a defensive weapon. The scientific name goes back to the type genus Acanthurus ( Greek ακάνθουρος , "the thorn- tailed "), first described in 1787 , whose name in turn is composed of the Greek άκανθα, ácantha , "the sting", and ουρά, ourá , "the tail". The family itself was established in 1810 by the French naturalist Constantine Rafinesque .
distribution
Doctor fish live exclusively in salt water and have a circumtropical distribution, so they can be found worldwide in waters close to the equator . Six species live in the Atlantic , the rest in the Indian and Pacific Oceans . The representatives of the family can be found in coral reefs and lagoons in the Red Sea , the Persian Gulf , on the coasts of East Africa , Madagascar , Japan , Hawaii and Australia .
Appearance
Appearance
Most types of surgeon fish reach a body length of 30 to 40 centimeters. The dwarfs in this family include the Japanese surgeonfish ( Acanthurus japonicus ) and Randall's surgeonfish ( Acanthurus randalli ), each of which only reaches a body length of up to 18 centimeters, as well as the smallest species, the Tomini bristle- toothed doctorfish ( Ctenochaetus tominiensis ), which is only 12 Inches long.
The giants in this family are species of nose doctor fish . The long-nosed doctor fish ( Naso annulatus ) reaches a body length of up to 1 meter, the horse-head nose doctor fish ( Naso fangeni ) is up to 80 centimeters long. The horn-like bulges on the forehead are typical and also eponymous for nose doctor fish - in some species they can become so large that adult fish are no longer able to pluck algae from corals or the subsoil with their mouths. There is therefore a change in diet from algae to plankton.
The high-backed and very narrow bodies are typical of surgeon fish. In the nasal doctor fish subfamily, the body is generally a little longer and therefore appears more spindle-shaped. There is usually no difference between the sexes in terms of body color in surgeon fish - however, males can become larger than females and their coloration can be somewhat more intense during the spawning phase. In the males of the nasal doctor fish, the nose-shaped protuberance on the forehead is often stronger and longer. In older males of the real surgeonfish , a so-called forehead bump can also occur. In some zebrasoma species ( Z. scopas and Z. xanthurum ) the males can be recognized by the fields of hair in front of the scalpel (Luty 2013).
All surgeon fish have the deep-set and very small mouth, in which the upper jaw is slightly longer than the lower jaw. It sits at the end of the head, which makes up about 15 percent of the body's length. Due to food specialization, some genera have developed specific dentition shapes. The snout of the sailfin doctor fish from the subfamily of the scalpel doctor fish is somewhat elongated so that they can also reach algae in less accessible places. The mouth of the bristle-tooth doctor fish from the same subfamily, on the other hand, is rather wide and they have movable rasp teeth to be able to rasp off algae like a mop.
Some species change color as they grow up. The blue surgeonfish ( Acanthurus coerulus ) is colored yellow during its juvenile life, thus resembles a species of fish that lives in reef crevices and, through this mimicry, signals to its predators that it is not very worthwhile prey. During this phase, the animals defend their territory resolutely against competitors, even if they are conspecifics. If their small territory no longer offers them enough food, they take on the color of the adult animals and then form swarms of food together with other species. A mimicry comparable to the blue surgeonfish is also shown by the circular thorn surgeonfish ( Acanthurus tennenti ) and the chocolate surgeonfish ( Acanthurus pyroferus ). As juvenile fish they resemble the dwarf angelfish , which are also very difficult to hunt down reef crevices.
The dorsal and anal fins can be spread out like a flag from the body during the imposing behavior . With the exception of the nasal surgeon fish, surgeon fish species have long, narrow pectoral fins. In contrast, the pectoral fins of the nose doctor fish are short and broadly rounded.
The scales of the surgeon fish species are very small. Due to the relative sterility of the sea water, surgeon fish species also have a thin skin and thin layer of mucus compared to freshwater fish.
The scalpels
Doctor fish have one to twenty sharp “scalpels” or spinous processes at the root of their tail, with which they can defend themselves. The "scalpels" are the result of the transformation of a scale and have razor-sharp cut surfaces. In nose and saw doctor fish, there are thorn-like horn plates, of which at least two are formed on each side of the body.
They are often highlighted in color and therefore easy to recognize. In the actual surgeon fish (Acanthurinae), the scalpel is mobile and applied to the body when at rest. Since the "scalpels" are not connected to muscles, but are simply anchored to the spine with tendons , the real surgeonfish cannot actively set them up for defense. Instead, they are passively erected by flapping their tails on the outwardly curved (concave) side of the tail peduncle at an angle of approximately 80 degrees.
The scalpels of the nose doctor fish are fixed, which means that their blades are always ready for use. The vast majority of nasal doctor fish have two blades on each side of the tail root. The saw doctor fish, on the other hand, have three to ten bony appendages on both sides of their tail roots.
The scalpels are used for defense against predators such as moray eels , groupers and barracudas , but also in intra-species disputes. It used to be assumed that surgeon fish slit open the bellies of other fish species with a scalpel in order to eat their entrails. That is not true - the scalpels are purely a defensive weapon of the fish.
If injured by these scalpels, symptoms of poisoning occur. The specialist book author André Luty points out that in a series of experiments with Prionorus scalpus, the fish injured by the scalpels all died, although the scalpels had neither poisonous conductors nor glands. This is probably due to the fact that protein compounds on the fish skin penetrate the wounds, lead to infections there or, as proteins, have toxic effects.
Other species such as the pallet doctor fish ( Paracantharus hepatus ) or some species of nose doctor fish also have poison glands on their dorsal fin spines. In humans, injuries from the spines of the fins or from the scalpels can be accompanied by severe and painful swelling of the affected limbs. The pain can persist for weeks.
nutrition
Doctor fish are food specialists, whereby the majority of the species switch to plant food after their larval phase, in which they mainly eat animal plankton . Vegetable food consists either of algae or of detritus , i.e. cellular decay products. Switching to a different food source is accompanied by physical changes:
- The transformation of the feeding habits can be followed by the relative length of the intestine from the young to the adult surgeon fish. An Acronorus (young fish) 3 cm in length has an intestinal length of approx. 10 cm; with a body length of 16 cm, the adult doctor fish already has an intestinal length of approx. 90 cm. This relatively large intestine length is necessary because the plant food is difficult to digest and the digestive system of the doctor fish can only process plant food with great difficulty. The length of the intestine therefore causes the food to remain longer and the food pulp is better utilized in the fish body (Luty, p. 19).
The diet also requires behavioral adaptations: some species eat their droppings in order to be able to use the half-digested food residues better ( coprophagia ). Many species of surgeon fish, which predominantly live on algae, also ingest coral sand in order to be able to process the cell walls of their plant-based food better. In addition, specific microorganisms have been found in the species of surgeon fish that live on the Great Barrier Reef, which live as symbiotic partners in the digestive tract and which are not found in species from other fish families.
Most species only use a few specific food sources. The Japanese doctor fish, for example, only eats the filamentous algae growth that occurs as fine algae fluff on natural reef rock. Randall's surgeon fish, on the other hand, needs a high proportion of calcium algae in its diet. For the gold spotted surgeonfish ( Acanthurus nigrofuscus ), the preferred food source is seasonal. In summer it eats red and brown algae , in winter it prefers green algae . If the green algae are not available to him in winter, this affects his ability to spawn. Due to the consumption of green algae, the fatty acid composition of the doctor fish fats changes. The gold spotted surgeonfish consumes this during the formation of its gonads (gonads).
A few species remain plankton eater after their larval phase - these include, for example, the pallet surgeonfish ( Acantharus hepatus ) and the monk surgeonfish ( Acanthurus gahm ). Some of the nasal doctor fish species switch from eating algae back to plankton food during their life because they can no longer eat algae from the substrate when the horn is fully grown. With increasing age, they become plankton eaters who satisfy their need for algae from the algae swimming between the plankton and by eating food organisms such as jellyfish, which can accommodate microalgae in the form of zooxanthellae .
behavior
The more than 80 types of doctor fish show a very large spectrum of different behavior patterns, some of which also occur within a species and depend on the age, the reproductive phase and the respective environmental conditions. Some species of surgeonfish have been observed to behave strictly territorial if the area remains below a certain density of individuals. If the frequency of the species increases, however, they form feeding swarms. Most often, however, surgeonfish can be observed as a single animal or as a pair and behave predominantly territorial.
Swarms
In the school surgeonfish can either be observed during the spawning season, or they belong to the species that form feeding schools.
The formation of feeding schools is advantageous if the fish can access feeding grounds in this way from which they would be driven out as individual fish by food competitors such as damselfish . This applies, for example, to the blue surgeonfish ( Acanthurus coeruleus ) or the white-throated surgeonfish ( Acanthurus leucosternon ). If, on the other hand, the fish have enough food available, the fish do not form swarms. For example, the convict surgeonfish ( Acanthurus triostegus ), whose feeding schools in the Maldives can contain up to 1000 fish, did not form schools during the coral death on these coasts in 1998 because there was sufficient food available due to the strong algae growth associated with the coral death.
It has also been found in the scientifically well-studied gold spotted surgeon fish that its behavioral repertoire is strongly influenced by its environmental conditions. In the Gulf of Eilat, for example, it was found for individual regions that this species of doctor fish divides its habitat into feeding and resting areas. At the beginning of the day, the entire population of up to 400 individuals from a section of the reef migrates to the feeding zone, eats there together and returns to the rest zone in the evening, where they go to their individual sleeping places. In other zones of this marine area, however, the gold spotted surgeon fish only forms small groups of 10 to 20 fish, which eat and rest in areas with a diameter of 10 to 20 meters. Only during the spawning phase do the populations in these regions form larger swarms.
Territorial behavior
Many types of doctor fish already behave territorially during their juvenile fish season and form mini-territories during this time, which they defend resolutely against competitors. This behavior is necessary because the young fish are not yet able to venture into the open reef due to the threat from predators and so the algae available to them are limited. The fish therefore defend a territory around their hideaway from their fellow species that provides them with sufficient food.
Harem districts
The development of harem territories has been observed in the Arabian surgeonfish and blue-stripe surgeonfish ( Acanthurus lineatus ) . The female fish have their own small territories, a single male controls and defends several of these territories. It swims through its territory in the same lanes and chases away competing species as well as other herbivorous fish.
Reproduction
Spawning phase
All types of doctor fish seek the free water to spawn. They are particularly endangered by predators. If the density of individuals within an area is correspondingly high, they therefore form schools in which the individual fish is better protected against them. If, on the other hand, the density of individuals is low, the fish spawn as a pair. The synchronization of the spawning behavior takes place via moon phases. Many species spawn at the full moon, which is associated with the highest tide change . The larvae are removed far from the reef by these tides. This, too, is an adaptation of behavior towards predators, as many other reef inhabitants would eat the larvae.
Among the surgeonfish species there are some in which the female is ready to spawn monthly , while in other species seasonal spawning cycles can be observed. These differences can even occur within a species as an adaptation to the respective habitat. For example, the females of the convict surgeonfish ( Acanthurus triostegus ) are ready to spawn in the warm waters near the equator all year round, while off the coast of Hawaii they only spawn between December and July.
The actual act of spawning usually begins with an act of showing off, in which the dorsal and anal fins are set up. Males and females swim in parallel. As is usual with many fish species that spawn in open water, the surgeon fish also swim two to three meters upwards for the actual spawning act, depending on the species, and at the highest point simultaneously shed eggs and sperm . Occasionally they even pierce the surface of the water. If the spawning act occurs within a larger swarm, it is always individual groups who do this at the same time and then return to the relative safety of the swarm.
For a number of the surgeon fish species, changes in body color have been described during the breeding season. This ranges from the lightened facial spot in the white-throated surgeonfish ( Acanthurus leucosternon ) and in the Japanese surgeonfish to clear color changes in the Indian sailfin doctor ( Zebrasoma desjardinii ), in which the contrasts of the light and dark head stripes become stronger and in which the tail fins then turn blue demonstrate. The masked nose doctor fish shows one of the most noticeable color changes : While the basic color is usually medium brown to olive brown, the dark blue markings on the body of the courting male can change to a spectacularly bright and iridescent blue.
Development of the larvae
The females of the surgeon fish species lay a very large number of eggs. In a convict surgeonfish female with a body length of only a little more than 12 centimeters, the number of eggs spawned was 40,000. These eggs have an oil ball that allows them to float freely in the water.
The time between spawning and larvae hatch depends not only on the species, but also on the water temperature. In the convict surgeonfish, larvae hatch at a water temperature of 24 ° C as early as 26 hours after spawning. These larvae first live on their yolk sac and start eating after five to six days. They feed on small crustaceans and juvenile fish floating in the plankton:
- The larvae return to the reef lagoons and mangrove forests of the coasts after about 2 - 2.5 months , where they find sufficient food and hiding places. The Acronurus [larvae] are disc-shaped, transparent and without scales, but have a shiny abdomen and have long been described as a separate fish species ... The transformation from Acronurus to the small Acanthurus takes place within 5 days. If the larvae are kept in the dark, they will not transform. Only after the metamorphosis do growth algae and thread algae form the main food. (Luty, p. 36)
Tribal history
The surgeon fish form the order of surgeon fish-like (Acanthuriformes) with eleven other recent fish families . The most important common feature of the order is the method of tooth replacement. In the larvae and adult specimens of these fish, the regrowing teeth grow on the outside of the jaw and replace their predecessors in groups. Other characteristics of the surgeonfish are widespread among the Acanthomorpha , but rarely occur in combination with the exception of the surgeonfish. These are: six branchiostegal rays or less, no tooth plate on the second and third epibranchials (the second bone from the top of the second and third gill arch ), an edentulous palatine bone, and the supramaxillary (a jawbone) is missing.
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Fossil record
The surgeon fish are known at the latest from the geological period of the Eocene , which began about 55 million years ago. The most important site is the Monte Bolca formation in northern Italy , which arose from Tethys deposits . It made it possible to describe numerous genera of fossil surgeon fish from this period, including Acanthuroides , Gazolaichthys , Mataspisurus , Metacanthus , Pesciarichthys , Protozebrasoma , Tauichthys or Tylerichthys .
The genera Proacanthurus and Sorbinithurus , known from the same formation , the latter about 52 million years old, can probably already be assigned to the modern subfamilies, namely Proacanthurus the scalpel doctor fish ( Acanthurinae) and Sorbinithurus the nose doctor fish (Nasinae).
The latter group probably also includes the genus Arambourgthurus , which dates from the early Oligocene around 34 million years ago and is known from the Iranian Ishtebanat Formation , which is also a relic of the Tethys Sea. The genus Marosichthys is known from the Miocene ; it was described from the Indonesian island of Celebes and proves the occurrence of the family in the western Pacific. Together with Sorbinithurus and Arambourgthurus it probably forms a monophyletic taxon, whose sister group is formed by the modern nose doctor fish and the fossil genus Eonaso . The latter was described from the Caribbean island of Antigua ; their age is indefinite, but the first occurrence probably falls into the Oligocene at the earliest and shows the existence of a West Atlantic line of development.
The phylogenetic classification of the fossils mentioned above can be seen in the following diagram:
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Systematics
In the internal system, scalpel and nose doctor fish are generally treated as subfamilies. The saw doctor fish represent a genus that is to be settled within the scalpel doctor fish, the bristle-tooth doctor fish are within the genus Acanthurus .
| Surgeonfish (Acanthuridae) |
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People and surgeon fish
Keeping in aquariums
Doctor fish are very demanding as aquarium fish. Keeping them in a species-appropriate manner places high demands on the aquarist . This is due, on the one hand, to their aggressive behavior towards conspecifics and other surgeon fish species, their pronounced swimming instinct and the high demands on the water quality in the aquarium. In addition, many species have a specific need for food. Vegetable supplementary feeding in the form of algae, dandelion, spinach or various salads is essential for most species. If several doctor fish are to be kept, which is considered species-appropriate, all specimens are best placed in the aquarium at the same time. So there is still no established hierarchy. If a doctor fish is later placed in an existing stock, the new one quickly becomes a “whipping boy” and can be killed.
All specimens offered in stores are wild-caught. The trapping of individuals from their natural territories is generally to be regarded as problematic. In addition, older wild-caught animals in particular find it very difficult to get used to life in the aquarium, since the germ density is much higher here than in the sea. Certain species, such as the white-throated surgeonfish, do not have a very high chance of survival in the aquarium and fall ill quickly due to exposure to microorganisms and pH value differences when the animals are moved too quickly, when the calcium supply (especially calcium hydroxide) or when the water is changed too quickly.
When keeping doctor fish, the national animal welfare laws must also be observed. According to the new Austrian Animal Welfare Act, since January 1, 2005, keeping doctor fish is only permitted from an aquarium size of at least 1,000 liters.
Doctor fish are susceptible to intestinal parasites in the aquarium. These parasites spread quickly in the aquarium among the related fish, which, as already mentioned, belong to the faeces eaters ( coprophagia ). This behavior contributes to the fact that parasites spread quickly again even in fish treated with appropriate medication.
Doctor fish as catch fish
Some types of doctor fish are used for human consumption. 13 types of doctor fish are fished off Hawaii alone and 6 species off Palau . Doctor fish also contain a large amount of n-3 polyunsaturated fatty acids . This makes them a potential supplier of raw materials for the manufacture of cardiovascular products.
As algae-eating fish, they occasionally ingest the fat-soluble and heat-stable poisons maitotoxin and ciguatoxin when they consume dinoflagellates and pass them on to their predators. This poison does not harm the fish themselves - however, humans are sensitive to it and can die of ciguatera .
swell
literature
- Joseph S. Nelson : Fishes of the World. 4th edition. John Wiley & Sons, Hoboken NJ et al. 2006, ISBN 0-471-25031-7 .
- André Luty: Doctor fish - way of life - care - species. Dähne, Ettlingen 1999, ISBN 3-921684-61-7
- André Luty: Doctor fish - in the coral reef and in the aquarium. Book on demand, Pro BUSINESS GmbH, Berlin 2013, ISBN 978-3-86386-478-1
- Andreas Vilcinskas : Marine animals of the tropics. Franckh-Kosmos, Stuttgart 2000, ISBN 3-440-07943-0
- Helmut Debelius , Rudie H. Kuiter : Doctor fish and their relatives. Ulmer, Stuttgart 2002, ISBN 3-8001-3669-4
- Helmut Göthel: Color Atlas Marine Fauna - Red Sea, Indian Ocean (Maldives). Ulmer, Stuttgart 1993, ISBN 3-8001-7266-6
- Stanislav Frank: marine fish. Werner Dausien, Hanau 1998, ISBN 3-7684-2940-7
Individual evidence
- ↑ Anthony Gill & Jeffrey M. Leis (2019): Phylogenetic position of the fish genera Lobotes, Datnioides and Hapalogenys , with a reappraisal of acanthuriform composition and relationships based on adult and larval morphology. Zootaxa, 4680 (1): 1-81. DOI: 10.11646 / zootaxa.4680.1.1
- ↑ Laurie Sorenson, Francesco Santini, Giorgio Carnevale, Michael E. Alfaro: A multi-locus timetable of surgeonfishes (Acanthuridae, Percomorpha), with revised family taxonomy. Molecular Phylogenetics and Evolution, Volume 68, Issue 1, July 2013, pages 150-160, DOI: 10.1016 / j.ympev.2013.03.014
Web links
- Doctor fish on Fishbase.org (English)
