Small-eyed umber
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Little-eyed umber ( Nebris microps ) |
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The small-eyed umber ( Nebris microps ) of the southern Caribbean is an important food fish from the umber family . The small size of the eyes of this animal (8–11% of the head length) is striking: μίκροψ "small-eyed" - smalleye croaker, corvina-ojo-chico.
The vicarious species Nebris occidentalis Vaillant , 1897 (up to 60 cm, more unevenly colored, eyes 8–10% of the head length; seldom marketed) lives on the American west coast (Guatemala to Peru ).
features
The body is elongated but only slightly compressed, the head very broad. The mouth is large, set steep (above). The teeth are small, they stand in two dense bands on the premaxillary and dentals. Pharyngeal dentition, on the other hand, is coarse and crushing. The gill trap is very well developed (tight). No barbels. The scales are very small and smooth ( cycloid ); also on the long D2 and the A. sideline : a total of approx. 120 scales (only every second one is pierced). Color: silvery with a distinct brown (or orange) tinge (especially on the back; νεβρίς, nebris, "light brown fur of a deer calf", see Nebris ). Ventral fins orange, often with a dark tip. C dark, rounded at the back, but with elongated central rays. The back of young animals is darkly spotted. The inside of the gill cover can be yellowish. Swim bladder in front on both sides with a long, circular extension curved back. Sagitta oval, thick, lapillus, on the other hand, slightly developed - up to 50 cm long (weight almost 6 kg), but usually only a maximum of 30 cm. Fin formula : D1 VIII-X, D2 I / 29-32, A II (weak) / 9-10.
Occurrence
This umber lives close to the coast (up to 50 m depth) sociable over sand and mud rich in detritus ; Young fish in particular prefer estuaries (need brackish water). Spawning is repeated in open water. The food is made up of mussels, snails, but especially smaller benthic crustaceans (e.g. shrimp). It lives in the southern Caribbean (Colombia to southern Brazil) and is particularly popular between Trinidad and the Orinoco estuary ("butterfish"). It is caught there with small ground nets and rods and mostly marketed fresh or salted locally.
The petty eyes
Such a noticeable small eyesight means poor eyesight - especially in animals that are predominantly nocturnal. Therefore, within a family like the Sciaenidae, significant small-eyedness is a phenomenon that requires explanation.
Many umbers live in (often) murky waters ( detritus-rich surf zone, mangrove , estuary areas of large rivers), but this is the reason for poor vision due to very small eyes in general in fish, and other mangrove inhabitants have large eyes, although their biotope is rare becomes transparent “enough”. On the other hand, the two Nebris species do not have any clearly “special” sensory channels that make good vision appear to be easily dispensable (cf. Amazon river dolphins ( Inia ): ultrasonic “sonar”; Acipenseridae , Mormyridae : electrical fields (“radar”)). So it seems that with Nebris the mandatory leg movements of the most important prey animals and the head-sideline system (with additional pores near the mouth), which is very well developed in most umbers, were sufficient to compensate for the reduction in eyesight (the head sidelines are similarly wide and only skin-covered like the ruff , which snaps moving prey in a targeted manner even in complete darkness). It is possible that the crustaceans could damage larger eyes (more easily) with their armored extremities. It remains unclear whether the striking (aberrant) design of the swim bladder front end could be relevant here. But he is not blind (as little as the dolphin mentioned). B. also perceive the approach of a predator optically and is therefore in no way to be understood as an evolutionary “on the way” to blindness. Blind fish are only found in caves, in the substrate (worm eels in sand), rarely in the deep sea ( not lightless thanks to bioluminescence ). The only blind (nonetheless light-sensitive) skull animal , with very narrow eyes, in the illuminated part of the sea is the scavenger (also hemiparasitic), e.g. T. nocturnal inger ( Myxine ), which also often digs into the sediment. Similarly, the living (yet) blind lamprey larva, the Querder .
