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  • Feb
    24
    Ultra-sensitive tubular eyes search for the silhouettes of prey overhead
     
    The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head. The fish's tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead.

    The barreleye (Macropinna microstoma) has extremely light-sensitive eyes that can rotate within a transparent, fluid-filled shield on its head. The fish's tubular eyes are capped by bright green lenses. The eyes point upward (as shown here) when the fish is looking for food overhead.

    A bizarre deep-water fish called the barreleye has a transparent head and tubular eyes. Since the fish’s discovery in 1939, biologists have known the eyes were very good at collecting light. But their shape seemed to leave the fish with tunnel vision.

    Now scientists say the eyes rotate, allowing the barreleye to see directly forward or look upward through its transparent head .

    The barreleye (Macropinna microstoma) is adapted for life in a pitch-black environment of the deep sea , where sunlight does not reach. They use their ultra-sensitive tubular eyes to search for the faint silhouettes of prey overhead.  Scientists had thought the eyes were fixed in an upward gaze, however. This would make it impossible for the fish to see what was directly in front of them, and very difficult for them to capture prey with their small, pointed mouths.

    Bruce Robison and Kim Reisenbichler of the Monterey Bay Aquarium Research Institute use videos from the institute’s remotely operated vehicles (ROVs) to study barreleyes off Central California. At depths of 2,000 to 2,600 feet (600 to 800 meters), the ROV cameras typically showed these fish hanging motionless in the water, their eyes glowing a vivid green in the ROV’s bright lights. The video also revealed a previously undescribed feature of these fish — its eyes are surrounded by a transparent, fluid-filled shield that covers the top of the fish’s head.

    In this image, although the barreleye is facing downward, its eyes are still looking straight up. This barreleye is about 6 inches

    In this image, although the barreleye is facing downward, its eyes are still looking straight up. This barreleye is about 6 inches

    Most existing descriptions and illustrations of this fish do not show its fluid-filled shield, probably because this fragile structure was destroyed when the fish were brought up from the deep in nets.

    Robison and Reisenbichler were fortunate to bring a net-caught barreleye to the surface alive. Over several hours in an aquarium on the ship, they were able to confirm that the fish rotated its tubular eyes as it turned its body from a horizontal to a vertical position.

    Barreleyes are thought to eat small fishes and jellyfish. The green pigments in their eyes may filter out sunlight coming directly from the sea surface, helping the barreleye spot the bioluminescent glow of jellies or other animals directly overhead. When it spots prey (such as a drifting jelly), a barreleye rotates its eyes forward and swims upward, in feeding mode.

    The findings were detailed recently in the journal Copeia.


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  • Feb
    24
    Carnivorous frogfish has forward-facing eyes and movies via jet propulsion
     
    The leglike pectoral fin for walking is the clue that this newly found fish is an anglerfish, even though it does not have a lure on its head for attracting prey.

    The leglike pectoral fin for walking is the clue that this newly found fish is an anglerfish, even though it does not have a lure on its head for attracting prey.

    Most fish have eyes on the sides of their heads, but a scientist now has confirmed a new and elusive species of carnivorous frogfish with eyes that face forward, like ours. The creature also has a fleshy chin and cheeks, adding to its strange appearance.

    The bizarre new species, Histiophryne psychedelica, made a brief splash a year ago when sport divers about 30 feet offshore of Ambon Island, Indonesia, photographed a shallow-water fish not seen before in 20 years of diving there.  Ichthyologist Ted Pietsch of the University of Washington’s Burke Museum of Natural History and Culture received pictures of the fish and guessed it belonged to the Histiophryne genus. Now he has confirmed this using genetic and morphological data, and fully described the freaky fish as a new species.

    “It is just an absolutely fantastic example of what natural selection can produce,” Pietsch told LiveScience. “And it’s a fantastic organism in its own right, and that is certainly enough to make it important.”

    Pietsch’s description of the animal, partly supported by the National Science Foundation, is detailed in the journal Copeia.

    Other oddities
    The fish is quite a sight: its extremely gelatinous skin is very fleshy, thick and loose; and the skin is covered with white stripes radiating from the eyes and continuing back to the body. This pigmentation could help the fish blend in among colorful, venomous corals on the sea floor in the area.

    “The Psychedelic Frogfish probably joins the long list of dishonest and harmless animals that have evolved to mimic the beauty of venomous animals,” said Leo Smith, assistant curator of fishes at The Field Museum in Chicago. “Pietsch and colleagues nailed this when they suggested that it looked just like the venomous corals found in its environment.”

    The fish also has some plastic abilities.

    “This animal seems to have ability to flare its face out and then pull it back again, so when it comes through a small crevice, those eyes become lateral and then it flares its eyes out,” Pietsch said. “It’s also probably a threat display — when it shows that oval face with the psychedelic striping, you think that’d scare something away.”

    The fish might have sensory structures along the outer margin of its face that would have a protective function like cat whiskers to enable it to sense the internal walls of a little cavern or a little space between coral, he said. Other fishes with forward-facing eyes include monkfishes and goosefishes.

    The fish’s jaws are lined with two to four irregular rows of small teeth, which it uses to consume smaller fish, shrimp and other marine life.

    The fish tend to hang out in pairs, and are often so well hidden that they could only be found when divers looked under rubble on the seafloor. Once uncovered, the fish immediately tried to wriggle out of sight by entering a crevice or hole via rigorous twisting and turning of the body and use of its pelvic fins to manipulate its position, like we would use our hands. Yet the fish later show no signs of damage.

    The fish get around in the sea via jet propulsion, or forcefully expelling water through openings in the body. The specimen that Pietsch studied was collected by his graduate student Rachel Arnold and photographed by David Hall.

    Mysterious origins
    People have been diving intensively in this region for more than 20 years, yet the new species was only noticed, near Ambon Island, last year by employees of Maluku Divers. In June 1992, staff at the Dallas Aquarium also noticed two frogfish with an unusual pigment pattern, found in a shipment of live fishes from Bali, Indonesia, but no one had time to examine them for years.

    So, it’s a mystery as to where the fish came from, Pietsch said. It could have been living for years in deeper waters, and then come into shallower waters recently for some oceanographic reason in the last season.

    “It seems that some of these animals do a bit of moving up and down into deeper water,” he said. “We know they come up in shallow water to spawn and reproduce, but that cycle should’ve been noticed in past years and it really wasn’t.”

    Many animals with brilliant pigmentation, like the new frogfish species, are toxic. The colors warn other animals not to eat them. However, there is no toxicity ever recorded with this group of animals, Pietsch said.

    “Although this doesn’t mean this thing doesn’t have toxicity on its skin,” he said. “A test is easy enough to do. You just touch your finger to it and then touch your finger to tongue. You get a burning sensation. I would do it in a minute.”

    Sadly, Pietsch has no access to specimens for now.


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