Upside-Down Catfish Doesn’t Care What You Think

You might suppose this catfish is sick, or just confused. But swimming belly-up actually helps it camouflage and breathe better than its right-side-up cousins.

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Normally, an upside-down fish in your tank is bad news. As in, it’s time for a new goldfish.

That’s because most fish have an internal air sac called a “swim bladder” that allows them to control their buoyancy and orientation. They fill the bladder with air when they want to rise, and deflate it when they want to sink. Fish without swim bladders, like sharks, have to swim constantly to keep from dropping to the bottom.

If an aquarium fish is listing to one side or flops over on its back, it often means it has swim bladder disease, a potentially life-threatening condition usually brought on parasites, overfeeding, or high nitrate levels in the water.

But for a few remarkable fish, being upside-down means everything is great.

In fact, seven species of catfish native to Central Africa live most of their lives upended. These topsy-turvy swimmers are anatomically identical to their right-side up cousins, despite having such an unusual orientation.

People’s fascination with the odd alignment of these fish goes back centuries. Studies of these quizzical fish have found a number of reasons why swimming upside down makes a lot of sense.

In an upside-down position, fish produce a lot less wave drag. That means upside-down catfish do a better job feeding on insect larvae at the waterline than their right-side up counterparts, who have to return to deeper water to rest.

There’s something else at the surface that’s even more important to a fish’s survival than food: oxygen. The gas essential to life readily dissolves from the air into the water, where it becomes concentrated in a thin layer at the waterline — right where the upside-down catfish’s mouth and gills are perfectly positioned to get it.

Scientists estimate that upside-down catfishes have been working out their survival strategy for as long at 35 million years. Besides their breathing and feeding behavior, the blotched upside-down catfish from the Congo Basin has also evolved a dark patch on its underside to make it harder to see against dark water.

That coloration is remarkable because it’s the opposite of most sea creatures, which tend to be darker on top and lighter on the bottom, a common adaptation called “countershading” that offsets the effects of sunlight.

The blotched upside-down catfish’s “reverse” countershading has earned it the scientific name negriventris, which means black-bellied.

— How many kinds of fish swim upside down?

A total of seven species in Africa swim that way. Upside-down swimming may have evolved independent in a few of the species – and at least one more time in a catfish from Asia.

— How do fish stay upright?

They have an air-filled swim bladder on the inside that that they can fill or deflate to maintain balance or to move up or down in the water column.

— What are the benefits of swimming upside down?

Upside down, a fish swims more efficiently at the waterline, where there’s more oxygen and better access to some prey.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/2018/04/14/the-mystery-of-the-upside-down-catfish

—+ For more information:

The California Academy of Sciences has upside-down catfish in its aquarium collection: https://www.calacademy.org/exhibits/steinhart-aquarium

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Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

For Pacific Mole Crabs It’s Dig or Die | Deep Look

Pacific mole crabs, also known as sand crabs, make their living just under the surface of the sand, where they’re safe from breaking waves and hungry birds. Some very special physics help them dig with astonishing speed.

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Among the surfers and beach-casting anglers, there’s a new visitor to San Francisco’s Ocean Beach shoreline.

Benjamin McInroe is there for only one reason — to find Pacific mole crabs, a creature commonly known as “sand crabs” — and the tiny animals whose burrowing causes millions of small bubbles to appear on the beach as the tide comes in and out.

McInroe is a graduate student from UC Berkeley studying biophysics. He wants to know what makes these little creatures so proficient at digging their way through the wet sand.

McInroe hopes that he can one day copy their techniques to build a new generation of digging robots.

— What are Pacific Mole Crabs?

Pacific mole crabs, also known as sand crabs, are crustaceans, related to shrimp and lobsters. They have four pairs of legs and one pair of specialized legs in the front called uropods that look like paddles for digging in sand. Pacific mole crabs burrow through wet sand and stick their antennae out to catch bits of kelp and other debris kicked up by the breaking waves.

— What makes those holes in the sand at the beach?

When the waves recede, mole crabs burrow down into the sand to keep from being exposed. They dig tail-first very quickly leaving holes in the wet sand. The holes bubble as water seeps into the holes and the air escapes.

— What do birds eat in the wet beach sand?

Shore birds like seagulls rush down the beach as the waves recede to catch mole crabs that haven’t burrowed down quickly enough to escape. The birds typically run or fly away as the next wave breaks and rolls in.

—+ Read the entire article on KQED Science:

https://ww2.kqed.org/science/2018/02/13/for-pacific-mole-crabs-its-dig-or-die/

—+ For more information:

Benjamin McInroe, a Ph.D. student at UC Berkeley, studies how Pacific mole crabs burrow
https://www.ocf.berkeley.edu/~bmcinroe/

Professor Robert Full directs the Poly-PEDAL Lab at UC Berkeley, where researchers study the physics of how animals and use that knowledge to build mechanical systems like robots based on their findings.
http://polypedal.berkeley.edu/

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—+ About KQED

KQED, an NPR and PBS affiliate in San Francisco, CA, serves Northern California and beyond with a public-supported alternative to commercial TV, Radio and web media.

Funding for Deep Look is provided in part by PBS Digital Studios. Deep Look is a project of KQED Science, which is supported by the S. D. Bechtel, Jr. Foundation, the Dirk and Charlene Kabcenell Foundation, the Vadasz Family Foundation, the Gordon and Betty Moore Foundation, the Fuhs Family Foundation Fund and the members of KQED.

Ruthe Cartoons – BUBBLES – Episode 02 – The Trap Door

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BUBBLES is a series about Barry and Sting, two dudes in a fishtank. In this episode, they are finding a trap door.

IDEA, SCRIPT, MUSIC AND DRAWINGS:
RALPH RUTHE http://www.ruthe.de

ANIMATION:
FALK http://www.couchkartoffelsalat.de

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ARNE CHRISTIANSEN https://www.youtube.com/sugartalker

Ruthe Cartoons – BUBBLES – Episode 01 – The Date

BUBBLES is a series about Barry and Sting, two dudes in a fishtank. In this episode, Sting has a date.

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IDEA, SCRIPT, MUSIC AND DRAWINGS:
RALPH RUTHE http://www.ruthe.de

ANIMATION:
FALK http://www.couchkartoffelsalat.de

VOICES AND TRANSLATION:
ARNE CHRISTIANSEN https://www.youtube.com/sugartalker