Uranoscopus Scaber

– Atlantic Stargazer –

Atlantic stargazer (Uranoscopus scaber) is a marine, subtropical fish of family Uranoscopidae. Its body is suited for living on the sea floor, and is one of few fish capable of bioelectrogenesis, or the ability to generate an electric charge.

Description

Typical of stargazers, its body is somewhat dorso-ventrally flattened, lacks a swimbladder,^[6] and has been found as large as 35.0 centimeters in length, but is usually between 20–30 cm.^[5] Its head and jaws are rotated upward, and has very large eyes and mouth. Its body is brown in color and can have numerous small light spots, with a lighter belly. It lives to about 5 or 6 years, and females are larger in size than males.^[7]

The uranoscope is a curious fish that the diver will only encounter out of the sand at night. Almost always buried , it features a massive pear-shaped body , with a huge head and a slender tail. The animal is up to 35 centimeters long . The mouth is very wide, in the shape of an upturned U , and the lower lip lined with teeth bears a fleshy growth supported by a fine filament. The eyes , protruding and slightly stalked , are located on the top of its flattened head .
The anterior dorsal fin is black, all other fins are fringed with blue . The lids are large, and their surface presents a marked relief. The color of the uranoscope is yellowish-brown, and its sides are mottled with black .

Distribution

It is widespread along the Atlantic coast of Europe and Africa, is very common in the Mediterranean and Black Sea, and somewhat rare in the Bay of Biscay.^[3] It is a demersal fish, which lives in sandy or muddy sand sediments along the upper slope of the continental shelf, between depths of 14–400 meters.^[4] It is not an economically important fish, primarily caught as by-catch, but is ecologically important.^[5]

Biotope

The uranoscope is a benthic fish that likes sandy and muddy bottoms, between 10 and 50 m deep. It is a sedentary species that goes unnoticed because it remains buried in sand or mud. Only his protruding eyes emerge from the sand.
Disturbed, he will burrow further, with surprising rapidity, using his pelvic fins.gre

Similar Species

The uranoscope has a very particular and characteristic anatomy, and the margin of error in identification is in theory very small. Buried, we could perhaps confuse it with the vives: Trachinus radiatus (vivacious with radiated head) and Trachinus draco (large vivacious).

Biology

Alimentation

The uranoscope is carnivorous. It is a predator all the more formidable as it is invisible. Only its eyes protrude from the sediment and it quietly awaits the passage of its future prey. To attract it, it shakes a fleshy vermiform growth above the sand. As it approaches, the uranoscope delivers an electric shock, which will instantly paralyze it. He will only have to open his gaping mouth to swallow it. The use of this discharge is not compulsory.
It also captures and ingests worms, molluscs and crustaceans buried in the sand which it grasps with the help of its lower jaw lined with clearly visible teeth.

Like other stargazers, it is an ambush predator which lies buried under sand with only its eyes showing. It has a large mouth, with a small strip of skin protruding from its lower jaw, which it moves in and out rapidly to act as a lure for prey. When a prey item comes near, the fish lunges toward the prey using a specially adapted vertebral column to generate the force by bending 60°, which takes less than 30 milliseconds to engulf the prey.^[8] It feeds primarily on fish larvae and smaller fishes, such as gobies, picarels, and small crustaceans,^[9] but has also been known to eat molluscs, echinoderms, annelids, algae and plant material.^[10]

Reproduction

They can spawn between April and September, depending on the region, and produce pelagic eggs, about 2 millimeters in diameter. After hatching, the larvae, post-larvae, and juveniles remain pelagic. Males are slightly more common than females, but this can vary within local populations.^[4]

The sexes are separate, with a slight sexual dimorphism: there are male uranoscopes and female uranoscopes, larger and more massive. Reproduction is sexual.
In males, sexual maturity is reached around 1 year, when they reach a size of 11 cm while in females it takes place around 2 years when their size is 14 cm.
The female can lay up to 125,000 eggs. Those who will be fertilized will give birth to fry which will lead a long pelagic life before approaching the bottom and burying themselves there. The longevity of females is greater than that of males (6 years on average against 4).

Various Biology

This fish is equipped with a particular organ, behind each eye, which produces acoustic impulses and electrical impulses.
There are 2 kinds of electric shocks: one of short duration of the order of a millisecond, caused by a mechanical stimulation, and the other of a longer duration, of the order of several seconds, observed only during the spawning period. The amplitude of the discharges also varies by sex.

The spurs of the pectoral fins are connected to venom glands. The uranoscope sting is poisonous for humans but not serious. The venom is mainly active during the spawning season: it causes painful swelling with a feeling of discomfort and dizziness. The two dorsal fins can also inflict painful stings, like those of the sharps, close cousins.

The uranoscope does not have a swim bladder.

When buried, the animal will use its two tubular nostrils to irrigate its gills.

Electric Organ

All species within the genus Uranoscopus, along with those in Astroscopus, have evolved electric organs, but lack receptor organs. These were both independently evolved, and are the only two genera within the order Perciformes to produce electric organ discharges (EODs). The Atlantic stargazer, like other bioelectrogenic stargazers, produces pulse-type EODs while feeding and when it is disturbed. The Atlantic stargazer produces EODs with the electric organ, derived from sonic muscles.^[11] In other fishes, sonic muscles are used to produce sound by agitating the swim bladder.

Further Information

The flesh of the uranoscope is edible, but its commercial value is very low.

This species can be presented in public aquariums, as in Crete (see photo).