Every Dead Animal I Can Get My Hands On

"Aside from background reading, just start cutting up the head muscles of every dead animal you can get your hands on -- that's the best textbook!"

These were the words of my summer research mentor for the University of Washington Friday Harbor Labs REU. I was thrilled to be selected as a research assistant for this competitive program. When I inquired to my mentor on how to best prepare for the internship, I expected a list of literature to read and maybe a couple practical skills to work on, like learning to drive a stick-shift car. But I was happy to oblige this hands-on approach!

Dead animal heads it is.

And three extras, just in case.

One of my fellow volunteers cooked a delicious Thai coconut fish soup for lunch yesterday and kindly saved me the six fish heads. I tracked down the fisherman today to ask what kind of fish these were, and he told me they were sol. They didn't remind me of the flatfish we call "sole" in English, so I did some research and I think they might be glasseye, Heteropriacanthus cruentatus, which is called tira al sol in Spanish.

My dissection lab.

Ready to cut up some dead animal heads!

I set up my own laboratory on the front porch, complete with tweezers from the turtle-capture kit, children's craft scissors, and a kitchen knife. I laid out newspaper and plastic bags as my lab bench, and used a couple biology dissection guides I found on the internet. I brought out a bucket of water and a rag so I wouldn't be smearing raw fish juice on my camera every time I took a photo.

I soon had a lab partner: the house cat, Panga.

Panga made sure to clean up all the scraps -- even the ones I wasn't quite done with yet.

My pre-dissection notes taken from online biology manuals.

The Gills

I started with the gills, since they were the easiest organ to investigate without cutting into the fish.

The scaly sheet of skin over the gills is called the operculum or gill cover.

When you lift the operculum, you can see the gills.

There are four gill arches on either side of the fish.

Here are the gills removed from the body.

Each gill arch contains gill filaments (feathery tissue on left) and rakers (poky appendages on right).

These are my gill sketches from after the dissection.

The Mouth

I read that a superior (upward facing) mouth indicates that the fish eats prey from below, whereas an inferior (downward facing) mouth means the fish eats prey from above. I think this fish's mouth is pointing slightly up.

Before cutting, you can see the maxilla (upper jaw), mandible (lower jaw), and tongue.

Isn't it weird how similar a fish tongue looks to a human tongue? Fish are our ancestors, after all.

After cutting, you can see down the throat past the gills.

Looking down the throat, you can see the gill rakers on the inside of the four gill arches.

Here is the mandible (lower jaw) separated from the body.

Rows of tiny, spiky teeth were evident when I pulled back the lips.

Here is the premxilla in full protrusion.

I noticed that I could protrude the premaxilla by putting pressure on the bridge of the nose, almost like a knee-hitting reflex. I couldn't capture it in a photo so I took the following video:

I first published this blog with an error when I referred to the above movement as "expansion." My REU mentor kindly notified me that "expansion" is what makes the gape larger (opening the mouth.) The movement in the above video is actually "protrusion" of the premaxilla.

My mentor also sent a link to this incredible video of a sling-jaw wrasse, Epibulus insidiator, from the Wainwright Lab at the University of California, Davis. Enjoy!

The Eyes

Save the coolest for last, right? I know I was supposed to be focusing on muscles and jaws, but the eyes couldn't be beat.

Two fish eyes -- before Panga ate one of them.

The optic nerve attached to the backside of the eyeball.

I had to put a lot of pressure on the eyeball for it to split open. It disintegrated into four major components: a fibrous outer skin (which I am assuming is the sclera), a clear liquidy gel (probably the vitreous humor), a watery black ink (part of the pupil?), and a hard transparent sphere (the lens).

From left to right: sclera, lens, vitreous humor, watery black ink.
This is the diagram from which I am making my educated guesses at anatomy.
Image credit: Wikimedia Commons.

These are the slimy, firm, transparent lenses from the fish eyes. Look how they refract light!

My favorite shot. Maybe this is how a fish reads the paper?