the magic of the flounder -- 7/25/17

Today's selection -- from What a Fish Knows by Jonathan Balcombe. When flounders are born, they have one eye on each side of their face. As they mature, one eye will migrate so that both are on the same side. They also have an astonishing ability to camouflage themselves, which is in part controlled by their vision:

"Baby flounders look like any other normal fish, swimming upright with one eye on each side. Then, in preparation for adult life, they un­dergo a bizarre transformation: one eye migrates to the other side of the face. It's like facial reconstructive surgery, only in slow mo­tion, and without scalpels and sutures. It isn't even always slow. The entire migration takes just five days if you're a starry floun­der, and less than one day in some species. If a fish can have an awkward adolescence, this one qualifies.
In exchange for the indignity of having both eyes nestled next to each other on one flank, flounders have fabulous binocular vi­sion. Like proud neighbors, the two eyes protrude from the body, and each can swivel independently. ... Binocular vision is a useful adaptation for a lifestyle of lying in wait on the sandy or stony bottom, exquisitely camou­flaged against the substrate, watching for an opportunity to snatch an unsuspecting shrimp or other unfortunate passerby with a lightning-fast lunge. With refined depth perception, a flounder can better judge the timing and wisdom of her ambush.

New Zealand flounder

"Ocular migration has obviously proven an effective survival strategy for flounders and related flatfishes, of which there are more than 650 species, including soles, turbots, halibuts, sand dabs, plaices, and tonguefishes. Some species are referred to as 'right­eye flounders,' always lying on their left side after their left eye migrates to the right side of the body. Others are lefteye floun­ders. Despite their fine adaptations, many Atlantic flounder and sole species are now threatened by overfishing.

Four frames of the same fish taken a few minutes apart showing the ability of flounders to change colors to match the surroundings

"[F]latfishes [are] the champions of pigment manipulation. They use their skin to melt chameleonlike into the background. I remember Flipping through a biology textbook when I was in high school and encountering a jaw-dropping photo of a flounder who had been placed on a checkerboard in his tank. Within minutes, the flatfish had produced a fine rendition of a checkerboard across his back. From a distance, the flounder effectively disappears. This ability to mimic backgrounds by changing the distribution of skin pigments is a complex and poorly understood process that in­volves vision and hormones. If one of the flounders' eyes is dam­aged or covered by sand, they have difficulty matching their colors to their surroundings, which hints at some level of conscious con­trol by the flounder rather than a cellular-level mechanism."



Jonathan Balcombe


What a Fish Knows: The Inner Lives of Our Underwater Cousins


Scientific American


Farrar, Straus and Giroux

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