Sky gazer (kind)
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Sky gazer ( Uranoscopus scaber ) |
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| Linnaeus , 1758 |
The sky-gazer ( Uranoscopus scaber ; = rough sky- gazer ) or, as one could say suggestively in the past, the " sea peacock ", may look strange or even "hideous" at first glance - but only as long as one does not understand the life requirements of his peculiarities suffice. In addition, this shape is not intended to be “seen” at all, since the fish lives buried most of the time - precisely so that it cannot be seen by predators or prey.
construction
The head is thick and rough, flattened at the top and almost cuboid . The gap in the mouth is almost vertical. The lower jaw is covered against the large, upper mouth opening with membranous fringes that prevent sand from falling into the mouth when the buried fish breathes. The eyes stand high on the head on small pedestals, but do not look directly upwards, but rather to the sides. Unlike Astroscopus , they cannot be drawn in and bulged. The nostrils (two on either side) are very small - the sense of smell can not play a significant role in Uranoscopus (compare with Astroscopus guttatus !).
At the upper end of the shoulder girdle protrudes from the thickened skin there, a poison sting directed backwards, the danger of which (for us) is controversial. Some consider him harmless; according to others, however, the sting causes severe pain and long-lasting swelling. An antiserum has been developed. The sky-gazer is by no means as dangerous as the weever .
The trunk is long conical (hence the name "uranoscope rat" ["rat"] in Cuvier 1833), covered with small cycloid scales (80-96 along the complete but weakly developed lateral line shifted towards the dorsal fins ), which are like trachinids result in a "herringbone" pattern. Only the caudal stalk is slightly flattened laterally, the rounded caudal fin (with strongly branched rays) is quite large - the fish has to accelerate strongly when it comes to eating, as it also has to overcome the resistance of the substrate in which it is located. But if the fish is frightened a few times in a row, it will soon be exhausted.
- Fin formula : D1 III-IV, D2 13-15; A 13-15; P 14–16, VI / 5, C 13.– 25–26 vertebrae.
The length reaches (albeit rarely) 40 cm, the weight over a kilogram (so it is significantly slimmer than Astroscopus , which weighs 9.6 kg with its maximum length of 56 cm, while Uranoscopus with this size - which it never reaches! - could only weigh 7.1 kg). The back is finely marbled brown and light gray, the sides of the trunk are overlaid with lighter bands; the belly is light yellow-gray. The large, rounded pectoral fins (with branched rays) are lined with white, the close-fitting, almost throaty pelvic fins are whitish, the unpaired fins are dark (brown). There is no space between the first and second dorsal fin. The triangular first dorsal fin is usually black, which can be interpreted as a warning signal ( vexillum ) for toxicity, especially since Bedini and colleagues interpret the same function (as Müllerian mimicry ) for the pectoral fin on the eye of the sole (Soleidae) (e.g. Solea impar ) who “threaten” with it even though they have no poisonous spines.
From the skull Gregory (1933) a fairly detailed account there (some functional aspects of s. Adamicka 1973). The length of the head (almost 1/3 of the total length) is due to the size of the breathing function of the Branchiostegal membrane . It is not clear why the outer cranial bones are "sculptured" as in primitive bony fish . Even Meckel (1833) pointed to a certain mobility of the anterior part of the lower jaw (dental, toothed) against the posterior (articular and angular), which are only connected by connective tissue and the flexible Meckel's cartilage. This structure is typical for Teleostei, but the mobility is particularly clear in the sky gazer and is to be understood in connection with the immobility of the suspensors and the violent snap at prey: this prevents the risk of breakage.
The swim bladder is missing. The pseudobranch is gill-like, the 4th gill arch only has gill leaves on the front edge. The teeth on the jaws, on the vomer and on the palatines are small, pointed (velvet teeth, i.e., arranged flat), which on the pharyngeal z. T. a bit bigger. The intestine is short, the stomach thick-walled, followed by 8–12 pyloric tubes . The size of the gallbladder is striking.
There are several genotypes with (2n =) 26, 27, 28, 30 and 32 chromosomes ; However, they can all be derived from the chromosome set of Trachinus or Echiichthys vipera , with 2n = 48 - by breaking and attaching the fragments to existing chromosomes.
Food acquisition and breathing
When the sky-gazer lurks buried in sand or finer gravel (but hardly any mud!) Except for the eyes and the horizontal part of the mouth crack, he can bring an esca (a “bait”) into play - a “worm dummy” “, Which reaches about 1/3 of the head length. It is a membranous extension of the mandibular valve, slashed and brightly spotted at the end - so it may resemble the tentacle crown of a tube worm , just as the mouth itself with its fringes may resemble the opening of a shell in the sand. During exhalation, the outer sides of the valves lie against each other and the extension lies in the direction of the flow in the oral cavity - it must therefore be "coughed out" forwards by briefly reversing the pressure conditions in this, but then hardly hampers further breathing; it plays in the breathing water flow (Günther 1886) and is certainly not, as also claimed, moved by "blood pressure fluctuations".
As soon as prey (many types of smaller fish or juvenile fish close to the bottom such as red mullets , gobies , horse mackerel , whiting , sardines , conger eels , flatfish and others; also octopus , shrimp and other crustaceans) is within reach, the sky-gazer suddenly breaks out of the sediment with its mouth opened by raising the head sharply in relation to the trunk (bending of the foremost spine): this causes the lower jaw to snap under the fish that "just wants to bite off the tentacle crown" (cf. also Astroscopus guttatus ).
Other special features come into play here. So has Uranoscopus , because he sometimes lurks even in very shallow, durchsonntem water, an eye-adaptation by nervous controlled iris -Motorik (otherwise rare in fish that yes rather, such as insects, adaptation mechanisms of the retina show - or autogenous Iris motor skills ; so most fish can not constrict their pupils ). The Maxillarmechanismus exists, but can because of the rigidity of jockstraps not very develop (it must also, as the gripping direction is not so directed upwards). The large gill cover is also immobile (because of the pressure of the sediment) - it only serves to allow the Branchiostegal membrane, which is attached to the hyoid, to play under the head. The paired hyoid with its six gill skin rays steered inside the jockstrap with great freedom of movement through a strikingly long stylhyale. When the fish digs in, it "blows" under its head (supported on its pelvic fins) with violent movements of its mouth, a cave in the sand, in which the Branchiostegal membranes then play (sucking in and squeezing out water, which passes through the four gill slits over the gill leaves flows). If the substrate is fine sand, the "used" water can only flow out from under the notched skin of the gill cover up to the sand surface, where it can then be noticed in two circular areas of "shimmering" sand. This "flickering" as well as (asymmetrical?) Movements of the small eyes are allegedly further attractants for prey (also already with trachinus ).
Reproduction and growth
Not much is known about a spawning prelude - but there must be such a thing - and that brings us to another surprising peculiarity of the sky-gazer. Astroscopus is the only genus of the barnacles with " electrical organs " (originated from transformed eye muscles ) and noticeable current discharges (also used in mating behavior) - with Uranoscopus one has now found something similar (albeit weaker), but does not yet know where it is Electricity is produced (the eye muscles are not transformed!). The electrical impulses differ depending on the sex. At the same time, Uranoscopus makes noises during spawning prelude, so that noises and electricity are likely to have the same cause. Of course, every muscle and even metabolic activity is associated with electrical phenomena, but only in the µV to mV range that the barbed fins cannot perceive, while the spikes we are talking about are in the V range and therefore also can be noticed by fish without electroreceptors. Baron and Mikhailenko therefore see Uranoscopus as a "transition form" to the macro-electric fish. The above also points to the strange and not uncommon phenomenon that with closely related living beings, physiological - ethological purposes (“goals”) can be achieved with very different (non- homologous ) organs.
The spawning season is early summer on the southern coasts of the Mediterranean, but larvae are found all year round on the northern coasts (Italy). The eggs released and fertilized at the bottom (at medium depths) are free-floating, rise to the surface of the water and soon give rise to translucent, plankton-eating larvae, which after several weeks approach the coasts and the bottom (especially seagrass meadows ) and are already "predatory" here . They only begin to dig in when they are juveniles a few centimeters long. Skygazers with a length of 15–20 cm, ie at the age of 1+, become sexually mature. The males and females grow at the same speed, but females become longer and much heavier. A large female can spawn up to 60,000 eggs (at one time), which (after swelling) are approx. 2 mm in size. The gender ratio is almost 1 (♀) to 2 (♂) (at least at the location of the investigation of Rizkalla and Bakhoum, the Egyptian coast). The oldest animals are not yet 6 years old.
Occurrence
The home of this fish is the Mediterranean Sea with its secondary seas (except only the brackish Azov ). It occurs everywhere (up to 400 m depth) where it can bury itself, even in not too polluted docks. However, the plight of untreated wastewater is clearly affecting him in some places. Although you cannot see it, it can (for example on the Black Sea coast) with its biomass stand in sixth place of the existing fish. It also occurs in the bordering Eastern Atlantic on the coast of Morocco (possibly still Mauritania ) and Portugal - further north to the south coast of Great Britain , increasingly rare. It is also said to be present around the Canaries and Madeira , but to the south it is represented by similar species.
Historical
The sky-gazer οὐρανοσκόπος was already well known in antiquity (at least) for the reason that it was recognized and sought after as a remedy for eye diseases because of its always skyward gaze and the large gall bladder (the eyes were coated with bile or preparations with it) - Evidence for this can be found in Hippocrates via Aristotle to Pliny the Elder and Athenaios . Perhaps the slime fish Callionymus lyra had the same reputation, since the so-called fish also has its eyes very high up on its head - or καλλιώνυμος was just another name for the sky-gazer. The old Tobias of the Old Testament, blinded by a corneal clouding, should, according to the speculation of the humanists, have been cured thanks to sky-gazing bile, although his eyes were treated with bile from a freshwater fish ( catfish ?). Uranoscopus appears in Conrad Gessner and Pierre Belon , but not in Francis Willughby (although John Ray mentions it).
literature
- A. Günther (1886): Handbuch der Ichthyologie. Vienna (Gerold).
- A. Sanz (1985): Contribución al estudio de la biología de Uranoscopus scaber Linnaeus, 1758 (Osteichthyes, Uranoscopidae) del Mediterráneo occidental. Invest. Pesq. 49: 35-46.
Individual evidence
- ^ R. Bedini, MG Canali and A. Bedini (2003): True and false threatening visual cues in some Mediterranean fish. J. mar. biol. ass. UK 83: 265-270. http://journals.cambridge.org/action/displayAbstract?aid=144847
- ^ WK Gregory (1933): Fish skulls . New York (Zool. Soc.).
- ↑ P. Adamicka (1973): Functional anatomical studies at the head of Akanthopterygiern (Pisces, Teleostei). Part IV. Uranoscopus scaber . Zool. Jb. (Anat.) 90: 580-606.
- ↑ V. Caputo et al. (2003): Chromosome banding and molecular cytogenetic study of two Mediterranean trachinoid fish species (Teleostei: Trachinidae, Uranoscopidae) . Cytogenet. Genome Res. 103: 139-143.
- ↑ L. Huet, V. Goosse, E. Parmentier and P. Vandewalle (1999): About some skeletal particularities of the first vertebrae related to the mode of prey capture in Uranoscopus scaber (Uranoscopidae). Cybium 23: 161-167.
- ↑ JZ Young (1931): The Pupillary Mechanism of the Teleostean Fish Uranoscopus scaber . Proc. R. Soc. London B 107: 464-485.
- ^ PR Møller (1995): Electric fishes: History and behavior. London (Chapman & Hall).
- ↑ VD Baron and NA Mikhailenko (1976): Uranoscopus scaber : a transitional form in the evolution of electric organs in fish. Docl. Akad. Nauk SSSR. 229: 983-986.
- ↑ SI Rizkalla and SA Bakhoum (2009): Some Biological Aspects of Atlantic Stargazer Uranoscopus scaber Linnaeus, 1758 (Family: Uranoscopidae) in the Egyptian Mediterranean Water. Turkish Journal of Fisheries and Aquatic Sciences 9: 59-66.
Web links
- Sky gazer ( Uranoscopus scaber ) on Fishbase.org (English)
- Marine species identification portal: http://species-identification.org/species.php?species_group=fnam&id=1914