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Saw VII: The Revenge of the Sawfish | BenchFly
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Saw VII: The Revenge of the Sawfish

This is a sawfish. I’m pretty sure it’s named for its large, chainsaw like, nose (I know, it’s not really its nose, but I’ll get to that in a second), but I could be wrong. And until recently, what the sawfish does with its saw has been a bit of a mystery.

Sawfish are a species of ray, and live in both salty and fresh water in the sub-tropics. What I incorrectly referred to as its nose is actually called a rostrum, and is an extension of the fish’s cranium. It is made of cartilage, save for the boney teeth that stud the periphery. But unfortunately this rostrum, due to its propensity to get tangled in fishing nets and lines, has resulted in a dramatic decline in the number of these fish, and they are now considered critically endangered.

For this reason, studying sawfish in the wild is extremely difficult. Different theories about the purpose of the saw-like rostrum have been postulated, including foraging through the muddy estuary floors that make up their primary habitat, or sawing flesh from large marine carrion (such as dead whales).

In a paper published this week in Current Biology, a group of Australian researchers report a rare opportunity to study newly-captured wild sawfish.

There are many examples of elongated rostra in jawed fish, including those of the prey-whacking billfish and the fish-sensing paddlefish. Scientists had thought, however, that these two features of the rostrum were completely separate. That is, no fish uses its rostrum for both attacking and detecting prey. But as Wueringer et al found, sawfish do.

Marine predators often detect their prey using electrical signals called dipoles. The researchers therefore used dipole decoys to study how the wild sawfish behaved towards their prey. Using the closely related shovelnose ray as a control, sawfish were shown mock prey either in the water column or close to the floor of the tank. When they detected prey, the sawfish didn’t just try and clamp its jaws around it as the shovelnose ray did. Instead, they swatted at the fish with their barbed rostrum: (Check video below of saw fish doing cool stuff)

But why? Aside from looking pretty cool, this behavior actually serves to stun the fish. This then lets the sawfish eat its dinner in the best possible orientation: Head first. Fish scales and fins are designed to allow them to move through water quickly, and are therefore oriented from front to back, so swallowing a fish tail first results in a nasty situation where these scales and appendages drag the wrong way.

So there you have it, folks. There is a right way to swallow a fish whole. I had no idea…

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Katie Pratt is a graduate student in Molecular Biology at Brown University. She has a passion for science communication, and in an attempt to bring hardcore biology and medicine to everyone, she blogs jargon-free at www.katiephd.com. Follow her escapades in the lab and online on Twitter.

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Be the first one to mind the gap by filling in the blank as a comment and get your name in the blog along with a sweet new BenchFly mug!

UPDATE: Congratulations to caffeinated lab rat – winner of this week’s Mind the Gap!

About the winner: My twitter is full of strange musings of a stressed out biochemistry PhD student in the life sciences. I study the role of opioids in brain development.

About the prize: In addition to fame and glory beyond their wildest dreams, winners receive our new hot-off-the-presses large (15 oz) BenchFly mug to help quench their unending thirst for scientific knowledge… or coffee. Check out where the mug has traveled – will you be the first in your state or country to win one?

Miss a previous edition of Mind the Gap? Shame on you! Don’t worry – we’ve got you covered:

Caution: Objects May Appear Larger Than They Really Are

Facebook Updates: The Good, The Bad, and The Vague

Scared of Dropping the Soap? Worry No More.

New Year’s Lab-olutions

A Social Network for Food: Why Won’t Vanilla Friend Garlic?

I’d Rather Die Fat and Young than Old and Skinny

Look Into My Wide, Vacant, Eyes

I’m Just Mad About Saffron

Sweet Relief: How Sugar May Help Reverse Climate Change

Laughter Really is the Best Medicine

All Work and No Play Makes Katie RSI Prone

Sexual Identity and Autocrine Stimulation: Oh, To Be Teenage Yeast

On Wine, Sunburns and the Tendency of Headlines to Mislead

Which Came First: The Opossum or the Snake?

Pigeons Know a Crazy Woman When they See One

To Boldly Go Where No Worm Has Gone Before

Another One Bites the Dust: Rinderpest Eradicated

Scientists Just Wanna Have Fun (Like Uncaged Monkeys)

Mosquitoes Eating You Alive? Cheesy Feet Could be the Problem

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6 comments so far. Join The Discussion

  1. caffeinated lab rat

    wrote on March 7, 2012 at 2:49 pm

    I love weird fish and their rostrums.

  2. alan@benchfly

    wrote on March 7, 2012 at 2:58 pm

    Hope you love new mugs too – you're the winner!

  3. caffeinated lab rat

    wrote on March 7, 2012 at 3:02 pm

    Oh my goodness, that's fabulous! I should be at the bench washing blots though! Sometimes goofing around in lab for a few minutes pays off!

  4. alan@benchfly

    wrote on March 7, 2012 at 3:22 pm

    See, who says goofing around doesn't pay?…

  5. Leticia

    wrote on March 7, 2012 at 2:50 pm

    Rostrum?

  6. Allie Wilkinson

    wrote on March 7, 2012 at 2:52 pm

    Rostrum

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