Cyclothone microdon
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Cyclothone microdon . Drawing: Tony Ayling |
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| Cyclothone microdon | ||||||||||||
| ( Günther , 1878) |
Due to its small size and widespread distribution, the meso pelagic Cyclothone microdon is perhaps the most populous fish species - many billions of specimens live in the upper part of the deep sea. They are too small to be fished efficiently; on top of that, their predators are decimated. Nevertheless (or because of it) there are only a few studies of their biology. William Beebe was the first to see them alive (1932): because of their small size and snaking ( anguilliform ) way of swimming, he initially thought they were worms.
features
The nature of the family of gonostomatidae (engl. Bristlemouths ) can be found from 200 to 5,700 m depth (at 0 to 6 ° C - it's so cold stenothermal ) - in contrast to many other deep-sea fishing it never rises to near the surface. It is very common between 500 and 2700 m depth, depending on planktonic copepods , its main food, most often below 1000 m. The numerous teeth in the mouth are very small, but the mouth itself is deeply split (English anglemouth ) and as long as the head (the mandibular stalk is directed backwards). The fish opens it wide, if the plankton density allows it, and then shoots the copepods with its gill trap (19–23 long branchiospins) all- inclusive out of the water; but otherwise he snaps them one by one. Beebe observed this from his bathysphere in 1932 , and in 1953 Günther and Deckert provided a functional analysis of food acquisition. For a 30 to 70 mm long fish, 2 mm long planktons are quite “big”. The color of the fish is silvery, with numerous large, star-shaped melanophores (brown), especially on the head and back. Especially along the edge of the abdomen there are numerous greenish and some reddish, species-characteristically arranged small luminous organs . The eyes are small, but quite functional. Instead of a swim bladder, fatty tissue under the skin provides buoyancy. The maximum length is 76 mm, the maximum age should be three years.
Fin formula : D 12-15, A 17-20, P 9-10, V 5-6, C (with clear pre-rays) ~ 34. 33–36 myomeres (corresponding to the number of scales on the line along the flanks).
ecology
Because of the maintenance of the nutritional animals, which also include ostracods and amphipods , the fish is not completely independent of the benthal , e.g. B. the mid-Atlantic ridge. With at least eight other (smaller), almost worldwide distributed species of this genus - as well as almost as many locally restricted ones - it fits into a synecological resource use scheme, into which we have hardly had any insight so far. The juveniles also have their own preferences - the distribution is very uneven in each case, and we do not know what stimuli are used to achieve it. C. microdon seems to be B. always below C. braueri , another very common species. Its occurrence is of course overdistributed in the km³ aspect, but equally distributed in the m³ aspect in order to be as unproductive as possible for predators. In the depth zone accessible to Beebe (500–900 m) there were (theoretically) always a few specimens in sight. Beebe also writes ( lc , p. 318) that in the dark he never noticed their luminous organs - either they are very weak or the fish can regulate them and only uses them temporarily. That the cyclothones are prey for all smaller predators of the deep sea - in addition to Alepocephalus , Argentina , Argyropelecus , Maurolicus and the like. a. - are very important, of course.
Multiplication
Cyclothone microdon does not have a defined spawning time, but continuously produces a few eggs, which then develop freely in the water into larvae (3 mm, worm-shaped). Sexual maturity occurs at a length of about 30 mm. The males become longer than females: they develop particularly larger olfactory organs (one inferred from this that female pheromones ). Prot (er) andrian gender changes occur in C. microdon .
distribution
This fish is found in all seas except the arctic one. The species is rare in the northern Indian Ocean, in the eastern South Seas and in the Mediterranean (too warm). C. pygmaea (30 mm long) was previously considered a Mediterranean subspecies of C. microdon .
Generic name
Cyclothone (Goode et Bean 1896) could mean, from ancient Greek, "a round piece of canvas ( othonē )"; which idea is to be associated with this remains unclear - for example filters (today: paper!) for funnels?
literature
- ^ W. Beebe: Half mile down. NY 1934, p. 317.
- ^ W. Beebe (1933): Preliminary account of deep sea dives in the Bathysphere with especial reference to one of 2200 feet.- Proc. Natl. Acad. Sci. USA 19: 178-188
- ↑ K.Günther and K. Deckert (1953): Morphological-anatomical and comparative ecological studies on the performance of the visceral apparatus in deep-sea fish of the genus Cyclothone (Teleostei, Isospondyli) .- Z. Morph. Ökol. Teres 42: 1-66.
- ^ J. Mauchline and JDM Gordon (1983): Diets of clupeoid, stomiatoid, and salmonoid fish of the Rockall Trough, northeastern Atlantic Ocean. Marine Biology 77: 67-78.
Web links
- Cyclothone microdon on Fishbase.org (English)