Northern Electric Stargazer
| Northern Electric Stargazer | ||||||||||||
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Northern electric stargazer, brought to the surface of the sand by the diver: caudal fin folded, first dorsal fin but erect "threateningly". You can also see the wrongly Y-shaped bone edges on the "forehead", which even give the southern stargazer its name: A. y-graecum . |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Astroscopus guttatus | ||||||||||||
| Abbott , 1860 |
The Northern Electric Stargazer ( Astroscopus guttatus ) is a fish of the western Atlantic and belongs to the spinefloss family of the skygazers (Uranoscopidae), which are probably related to the sand eels (Ammodytidae). He has an astonishing range of his own, and in some cases unique, adaptations. Like all uranoscopids, it is considered a good food fish, but is rarely caught due to its way of life.
construction
Like the sky-gazer of the Mediterranean Sea ( Uranoscopus scaber ), this stargazer is very compact and even broader than the other. It becomes over 50 cm long and 9 kg in weight. The back line is straight. The square head is "armored" with sculptured bone plates. The upper, large mouth is vertical, as it is only appropriate for a burrowed, lurking shock robber. There are some larger teeth near the front end, but the rest on the jaws are small. When the stargazer snaps at the prey, it throws its head "backwards" and at the same time rushes out of the sediment, because this allows the lower jaw to get under the prey to be grabbed even faster (cf. Malacosteinae ; this fish can hardly "suck") . The maxillary apparatus is activated, the forward extension of the upper jaw is minimal. The eyes, which are quite apart from each other, are very small, lie just behind the upper jaw and, if necessary, can be raised a little - above the sand surface. When fishing, you can sometimes feel unpleasant as soon as you get your hands on it that it is producing noticeable electricity (see the section on getting food ).
In addition, Astroscopus has become known as a fish that can "breathe (in) through the nose" because an (accessory?) Nasal sac flows into the front of the oral cavity (see fish nose ). The fact that the rear nostril had migrated into the mouth, which Atz suspected, is not true (see below). The nostrils and the mouth fissures are protected from the penetration of sand by small skin flaps (fringes) and at the same time they are camouflaged: they resemble the opening of a clam. The fish defends itself against enemies with a lateral sting (blunt, skin-covered, with poison gland) dorsally on the cleithrum (shoulder girdle) above the pectoral fin.
- Fin formula : D1 IV-V, D2 I / 12-13, A 13, P 18-20, VI / 5, C 19.
The pelvic fins (V) stand far forward (jugular) and are quite strong. The trunk and tail are covered with small, smooth scales that draw a diagonal stripe ("herringbone") pattern on the sides. The indistinct side line runs high on the back over ~ 110 cycloid scales . The spine comprises 25 elements. A swim bladder is missing.
Back and sides are (mostly dark) brown, with irregularly distributed light spots ( guttatus "speckled"); the belly is light. The large, rounded pectoral fins (dorsally longest: "shovel-like") are distal dark but lined with white, the pelvic fins light; the caudal fin (with a curved rear edge) is often banded light-dark (in juvenile fish also the tail), the soft dorsal and sometimes the anal fin are lined with dark, while the small triangular front dorsal fin is usually black. Since it resembles that of Trachinus vipera , where it has poison glands, it has been referred to as Müller Mimicry . Wrongly if there is a closer relationship, because then there would only be a change in function.
Food acquisition
Mainly small fish serve as prey, from time to time squids and crabs, which it does not attract with a worm-shaped skin flap of the lower jaw valve like the sky -gazer. It was therefore thought that as soon as it was close enough to the mouth, it would paralyze it with electric shocks. Because every fisherman immediately realizes that he is able to deal light strokes when he catches him. The electric shocks are generated by electrical organs that form in juvenile fish from straight eye muscles in a pocket behind each eye. The eyes do not have to be very mobile, as they only look up from the substrate anyway. But then it turned out that he uses the current surges (up to 50 V) to scare off larger fish that could endanger him. The discharge frequency is temperature-dependent: 50 Hz at 15 ° to over 500 Hz at 35 °, which is already close to the upper temperature limit. The strength of the current in the water is not sufficient to paralyze prey - but outside the water it can very well cramp the hand of someone who has touched it clumsily for a while. It is also obvious that the stargazer communicates electrically with his peers, for example to achieve equal distribution in the biotope or to come into contact with sexual partners - even though he has no electroreceptors at all. Measurable electrical activity when approaching a prey, on the other hand, is perhaps intended to "confuse" it.
Breathing and smelling
After catching prey or disturbance, it digs itself in again in no time with shoveling movements of its pectoral fins. That he (like our sky-gazer) cannot breathe in the usual way with fish, namely by raising and lowering the jockstrap (see fish mouth ) and gill cover , is clear, since the pressure of the substrate excludes these lateral movements (see the detailed Description of the skull by Gregory 1933). Breathing can only take place under the head by means of the hyoids and the Branchiostegal membranes , so it is single-phase - but the fish has a low energy turnover when lurking anyway. The strong ventral fins undoubtedly help to keep the breathing space free when digging in; This is also the purpose of heavy breathing, which blows the sediment away from under the head.
The respiratory water flows through the gills (cover) split off, with finer sand and silt, of course, only dorsally, where the resistance is least - the fish may therefore “betray” itself through two small round zones of 'shimmering' sand. On the other hand, the representation is incorrect, he would have two "siphons" pointing backwards and upwards for exhalation. Allegedly he uses sand flickering and even one-sided "eye rolling" (with the eye further away from the victim) to attract prey. Also Trachinus to as procedural and prey by twisting its iridescent cornea "beguile".
Inhalation also takes place through the nose - but never only through it, because the passages would be much too narrow because of the viscosity of the water. It is also questionable whether the mouth can be closed completely. However, there are very translucent buccal valves with a non- return valve function. By means of nasal breathing, the fish could also smell (“smell”) prey in the dark or in water turbidity - but it is still unclear to what extent this ability is pronounced. As a result of the immobility of the jockstrap, the normal olfactory mechanism of the barbedfish (with movements of the lacrimale, see fish nose ) has failed. It seems plausible that the connection between nose and oral cavity was created for this. He also uses this connection to press water into the orbit - because the posterior narine flows into it: for the aforementioned lifting of the eyes.
Spawning business and development
It spawns on the bottom in late spring or early summer, but the eggs are pelagic and slowly drift up to the surface. The transparent larvae live on the yolk sac up to their length of 5-7 mm. Then they feed on plankton and necton , and they also turn out to be cannibals. The skin turns dark, but a bright yellow spot appears on the chin. From a length of 12-15 mm, the mentioned eye muscles are transformed into electroplaxes , which are physiologically peculiar again, but still have the greatest similarity to those of the electric rays . The young fish approach the coast and the sandy bottom, especially seagrass meadows (near or in reefs). During the growth, the eyes remain behind, reach more and more the top of the head and the fish finally begin - migrating into deeper water - to dig themselves for food, where they then live for several years and spawn annually.
Distribution and related species
The fish is found in the western Atlantic from New York to North Carolina . It lives epibenthically at depths of up to 100 m (mostly 7–40 m) on fine to coarse sand or fine gravel.
The three other American species of Astroscopus (see Uranoscopidae ) are very similar in color and way of life .
etymology
It should be noted that there is also the generic name Asteroscopus - among the owl butterflies ( Noctuidae ). The semantic difference is that astero- is derived from ἀστήρ "star", astro- but from ἄστρον "constellation" - so these fish would actually be "constellation-watcher".
Web links
- Northern Electric Stargazer on Fishbase.org (English)
swell
- ↑ like Uranoscopus : L. Huet, V. Goosse, E. Parmentier et 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. - The first five vertebrae are adapted accordingly.
- ↑ by JW Atz (1952): Internal nares in the teleost, Astroscopus .- Anatomical record 113: 105-115
- ↑ Biology: http://www.flmnh.ufl.edu/fish/Gallery/Descript/StarGazerNorth/StarGazeNorth.htm
- ^ U. Dahlgren and CF Silvester (1906): The electric organ of the stargazer, Astroscopus (Brevoort). In: Anatomischer Anzeiger 29: 387-403
- ^ EG White (1918): The origin of the electric organs in Astroscopus guttatus . Publ. Carnegie Inst. Of Washington 252: 121 ff.
- ↑ a b c IR Schwab (2004): If looks could kill ... Br. J. Ophthalmol. 88: 1486. doi : 10.1136 / bjo.2004.057232
- ↑ http://www.archive.org/stream/fishskullsstudyo00gregrich
- ↑ http://www.flmnh.ufl.edu/fish/Gallery/Descript/StarGazerNorth/StarGazeNorth.htm
- ↑ Bernd Kramer (1996): Electroreception and Communication in Fishes. (Progress in Zoology, vol. 42 - Stuttgart; Jena; Lübeck; Ulm: G. Fischer.)