Labyrinth organ

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The labyrinth organ (short labyrinth ) of the labyrinth fish (Anabantoidei) and the snakehead fish ( Channidae), two sub- taxa of the Anabantiformes within the perch relatives (Percomorphaceae), is used for the air breathing of these mostly small fish that live in stagnant and eutrophic and therefore oxygen-poor waters . The pools of climbing fish and bush fish (Anabantidae) are sometimes even threatened with dehydration, so that these fish then have to be able to crawl over land in order to reach bodies of water. In gill sacs there are similar suprabranchial organs for breathing , which also allow overland crawling to search for remaining ponds.

This labyrinth organ lies (in pairs) in the skull just behind the ear labyrinth (see inner ear ), which is common to all vertebrates . The gill cavity is widened dorsorostrally to accommodate a “crumpled” bone plate that extends from the epibranchial II (the bone support of the upper branch of the second branchial arch). The bone plate (like the cavity itself) is covered with a respiratory (blood vessel rich) mucous membrane. As a result of the firm support, it cannot collapse like the gill leaves . The blood supply corresponds to that of the 2nd branchial arch . The suprabranchial space is used to take up an air bubble from the surface of the water with the mouth - the “used” bubble is (mostly) released at the same time through the gill (lid) cleft. Although the volume of the bladder can approach that of the swim bladder, the anabantoids all also have a narrow, elongated swim bladder and a well-developed, heavy skeleton. The labyrinth only becomes functional in the course of the juvenile development and is well developed depending on the species; only with Sandelia it is almost completely absent.

Some labyrinth fish (e.g. paradise fish ) suffocate even in "clean" water without the possibility of this air breathing. At first it was thought that the enlargement of the mucous membrane was used for smelling (similar to the conchae of human noses) - the giant gourami was therefore given the scientific name Osphromenus (“smell”). Lacépède (1801) made a mistake, however, so that the valid name is now Osphronemus . Coincidence would have it that this name also makes sense, even more than the original: Osphronemus could mean “[fish with] olfactory threads, rays” - and in fact (much later) it turned out that the long ventral rays are palatable of food on the ground. The facial nerve ( nervus facialis ), which innervates the facial muscles in humans, sends branches to the skin (especially of fins) in fish.

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