Jellyfish fish

from Wikipedia, the free encyclopedia
Jellyfish fish
Nomeus gronovii

Nomeus gronovii

Systematics
Spinefish (Acanthopterygii)
Perch relatives (Percomorphaceae)
Order : Scombriformes
Family : Galley fish (Nomeidae)
Genre : Nomeus
Type : Jellyfish fish
Scientific name of the  genus
Nomeus
Cuvier , 1816
Scientific name of the  species
Nomeus gronovii
( Gmelin , 1789)

The shepherd's fish or jellyfish ( Nomeus gronovii, from Greek Νομεύς, shepherd '), a 40 cm long representative of the galley fish within the Scombriformes , is widespread, but still holds some biological secrets. He is known for his coexistence with the state jellyfish ( Siphonophora ) Physalia (the " Portuguese galley " - hence also "galley fish"). In the species name, Johann Friedrich Gmelin , who was primarily a botanist , immortalized the memory of two Dutch colleagues, namely Jan Frederik Gronovius († 1762) and his son Laurens Theodor Gronovius († 1777): All three were colleagues and friends of Carl von Linné .

features

The jellyfish fish shows the shape of the "stromateoids" with a rounded head profile, but differs due to its split dorsal fin and (especially in youth) large, black pelvic fins, which are even fused with the belly through skin. During growth, however, the pelvic fins remain behind and the pectoral fins increase. The silvery fish is spotted dark blue, especially when young; later the whole back is dark blue, the sides are still with black spots for a long time. The black-edged caudal fin is deeply split. The sideline runs over 57 or 58 scales. The head is partially scaled. The jaw teeth are small, but form fine nippers in a row above and below. Vomer and Palatine are finely toothed, the Basibranchialia are edentulous. On the first gill arch there are 24–28 branchiospins . The spine consists of 41 elements (similar to that of relatives).

  • Fin formula : D1 IX – XII, D2 I / 24–29, AI – II / 24–29, P 21–23, VI / 5.
  • Nomeus gronovii (Man-of-war fish) .gif
  • Nomeus gronovii north carolina.jpg

Way of life

The larvae hatch in open water near the coast. From a certain size they look for connection to specimens of the blue state jellyfish Physalia physalis , which gives them protection thanks to their strong nettle batteries. Aquarium observations (Jenkins 1983) showed, of course, that Nomeus then not only eats plankton, but also bites off parts of the jellyfish's polyps and gonads, i.e. behaves in an ectoparasitic manner. (Thanks to their ability to regenerate, this is by no means dangerous for the siphonophores.) It seems that Nomeus does not acquire jellyfish slime as a protective layer (see Amphiprion ), but only avoids the nettle threads and is also quite insensitive to occasional contact. Another advantage of the fish may be that the scales are embedded very loosely and easily turned out (the scales can be easily replaced). Nevertheless, it also happens that a ("careless"; weakened?) Nomeus is eaten by the jellyfish. When a jellyfish is stranded, the fish stays under it to the shore and only then escapes. However, the sexually mature animals seem to penetrate into the deep sea (1000 m) even without jellyfish, they eat necton (crabs, fish, salps , hydrozoa, etc.).

distribution

Together with the state jellyfish, the shepherd fish occurs particularly in the subtropical western Atlantic and then drifts with the Gulf Stream . But it is also known from Brazil, the Canary Islands, São Tomé and South West Africa, as well as from the Indian and Pacific Oceans (especially the northern hemisphere). It is absent in the Mediterranean.

literature

  • Robert L. Jenkins: Observations on the commensal relationship of Nomeus gronovii with Physalia physalis. In: Copeia . Vol. 1983, No. 1, 1983, pp. 250-252, JSTOR 1444723 .
  • Richard L. Haedrich: Nomeidae. In: Peter JP Whitehead, Marie-Louise Bauchot, Jean-Claude Hureau, J. Nielsen, Enrico Tortonese (eds.): Fishes of the North-eastern Atlantic and the Mediterranean. = Poissons de l'Atlantique du nord-est et de la Méditerranée. Volume 3. UNESCO, Paris 1986, ISBN 92-3-002309-4 , pp. 1183-1188.
  • Yusuke Suda, Hiroyuki Tachikawa, Osamu Baba: Adult form of the stromateoid fish, Nomeus gronovii, from the North Pacific. In: Ichthyological Research. Vol. 33, No. 3, 1986, ISSN  1341-8998 , pp. 319-322, doi : 10.1007 / BF02904169 .

Web link