Nezumia sclerorhynchus
| Nezumia sclerorhynchus | ||||||||||||
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Nezumia sclerorhynchus , bycatch of a fishing trawler off the Catalan coast. |
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| Scientific name | ||||||||||||
| Nezumia sclerorhynchus | ||||||||||||
| ( Valenciennes , 1838) |
Nezumia sclerorhynchus is a deep-sea fish fromthe grenadier family (Macouridae). It occurs both in the Mediterranean and in large parts of the Atlantic and is often found as bycatch in the nets of deep-sea fishermen. This species is characterized, like other representatives of the Macrouriden, by a large head with a pointed snout and an elongated tail without a caudal fin . Instead, the second dorsal and anal fin extend the entire length of the tail. Nezumia sclerorhynchus lives (bentho) pelagic , that is, free-swimming over the ground in the deep sea from around 250 meters below sea level.
features
The maximum measured length for Nezumia sclerorhynchus is 36 cm, although this species can likely grow even larger. The exact length is usually difficult to determine, as parts of the body, especially the very thin end of the tail, often tear off when caught. The body is almost invariably covered with relatively large semicircular scales . Its coloration and that of the first dorsal fin are very dark, often black or dark brown with a silvery sheen, in the abdominal area sometimes with a purple tint. The remaining fins are pale to blackish. The snout is short with a blunt tip, with the underside not scaly. This is an important distinguishing feature from the closely related and outwardly very similar species Nezumia aequalis , whose habitat partially overlaps that of Nezumia sclerorhynchus , which means that both species can easily be confused. Nezumia sclerorhynchus has two separate dorsal fins, the first being comparatively high and pointed. It consists of two front hard rays , of which the second is serrated, and nine to eleven soft rays. The pectoral fins usually have 16 to 20 soft rays, the pectoral fins nine, in rare cases less. The attachment of the anal fin is approximately at the level of the rear end of the first dorsal fin. From there the anal fin, consisting of numerous soft rays, runs to the rear end of the elongated tail. A little further back is the second dorsal fin, which is also softly radiated and also extends to the end of the tail. A caudal fin is completely absent. As with other representatives of the Macrouridae, all organs of Nezumia sclerorhynchus are in the front third of the body. The two rear thirds are all accounted for by the muscular tail. As a result, the anus is located just behind the pelvic fins, between which there is a single luminous organ , the function of which is unexplained. The head is quite large with eye-catching eyes that cover about a third of the length of the head and are level with the corners of the mouth. The mouth is small, terminal and provided with small conical teeth on the inside. There is also a goatee on the lower jaw . Nezumia sclerorhynchus is sexually separated without pronounced sexual dimorphism.
distribution and habitat
Nezumia sclerorhynchus is distributed both in the entire Mediterranean and in large parts of the North and Central Atlantic from Portugal to the Gulf of Mexico and from West Africa to French Guiana . The species prefers the deep sea as a habitat and has been caught in areas between 130 and 3600 m, with it being most common at depths between 450 and 750 m. The largest individuals prefer greater depths. Nezumia sclerorhynchus is one of the most common and most individual species in this area of the deep sea.
Like other representatives of the grenadier fish, Nezumia sclerorhynchus also lives free-swimming near the sea bed.
nutrition
Nezumia sclerorhynchus is similar to closely related species - e.g. B. Nezumia aequalis - a generalist. By examining the stomach contents of caught specimens, very precise conclusions can be drawn about the diet of this species. Nezumia sclerorhynchus feeds mainly on amphipods ( amphipods ) and copepods (copepods). Both groups are important components of the zooplankton . Also hover shrimp (Mysida), which also belong to the zooplankton, make up a large part of the diet. Isopods (Isopoda), snails (Gastropoda), mussels (Bivalvia) and echinoderms (Echinodermata) spurned Nezumia sclerorhynchus also not. In rare cases, plant fibers can even be found in open stomachs.
About two thirds of the organisms found are of pelagic origin, the rest is either benthic or occurs both in open water and on the bottom. It can be assumed that Nezumia sclerorhynchus actively hunts its prey by swimming or tracks it down in the sediment with the help of its goatee .
Reproduction
Nezumia sclerorhynchus has separate sexes, with males and females occurring in a ratio of about 1: 1. The animals become sexually mature around the age of five years and a length between thirteen and fifteen centimeters. The maximum age of this species is unknown, but like many other species in the deep sea it is likely to be quite high. In contrast to other representatives of the Macrouridae, which reproduce seasonally, Nezumia sclerorhynchus has females ready to mate all year round. Almost nothing is known about the exact process of mating or the laying and fertilization of the eggs.
Eggs and larvae
The eggs of Nezumia sclerorhynchus are spherical, transparent and float freely in the water. Their diameter is about 1.6 mm. The chorion is smooth. In the yolk sac there is an oil droplet 0.32 mm in diameter, which the egg needs for buoyancy. The yolk is homogeneous in structure. The perivitelline space is relatively large. The larvae of Nezumia sclerorhynchus have only been described until they reach the so-called yolk sac stage, i. H. the stage at which the larvae have hatched but are still feeding on yolk. These larvae have a dark spot on the back above the stomach, a dark colored stripe in the middle of the tail, and spots on the abdomen and on the head. All descriptions of the appearance of the larvae in later stages of development are speculations based on the characteristics of adults or larvae of other macrourids.
Economic importance and risk
Nezumia sclerorhynchus is of no economic importance, but it regularly ends up in the nets of deep-sea fishermen as bycatch. An example of this is the gambas fishery off the Catalan coast, in which, in addition to the actual catch, Aristeus antennatus (a species of shrimp, see gambas ), a large number of other deep-sea organisms are brought to the surface. The by-catches, which very often include Nezumia sclerorhynchus , are usually thrown back into the sea unused. The effects of this on the Nezumia sclerorhynchus population have not yet been clarified. At the moment the stock is not considered endangered.
Individual evidence
- ↑ Geistdoerfer, P. (1990). Check-list of the fishes of the eastern tropical Atlantic (CLOFETA).
- ↑ a b c d G. D'Onghia, M. Basanisi, & A. Tursi: Population structure, age and growth of macrourid fish from the upper slope of the Eastern-Central Mediterranean . In: Journal of Fish Biology. 56 (5), 2000, pp. 1217-1238.
- ↑ a b c d T. Iwamoto: Vol.10. Gadiform fishes of the world (Order Gadiformes) An annotated and illustrated catalog of cods, hakes, grenadiers and other gadiform fishes known to date . FAO species catalog, 1990, ISBN 92-5-102890-7 , pp. 284–285 ( PDF )
- ↑ Marques, AM, & Almeida, AJ (1998). Notes on the biology of Nezumia sclerorhynchus and Nezumia aequalis (Gadiformes: Macrouridae) from the Algarve slope, northeast Atlantic. Cybium, 22 (1), 21-29.
- ↑ Saldanha, L., Almeida, AJ, Andrade, F., & Guerreiro, J. (1995). Observations on the diet of some slope dwelling fishes of southern Portugal. International Review of the Entire Hydrobiology and Hydrography, 80 (2), 217–234.
- ↑ Madurell, T., & Cartes, JE (2006). Trophic relationships and food consumption of slope dwelling macrourids from the bathyal Ionian Sea (eastern Mediterranean). Marine Biology, 148 (6), 1325-1338.
- ↑ Basanisi, M., Matarrese, A., & Megli, F. (1999): Reproductive strategies in macrourid fish: seasonality or not ?. Marine Ecology Progress Series, 184, 189-196.
- ↑ Fahay, MP (2007). Early stages of fishes in the Western North Atlantic Ocean (pp. 614-647).
- ↑ https://apiv3.iucnredlist.org/api/v3/taxonredirect/198598
