Fish dissection

Anatomy in general is quite interesting, and a fish dissection is an activity that allows one to explore and learn. It also helps one develop a better understanding of the human anatomy as a whole.

While fish anatomy isn’t human anatomy, it’s not extremely difficult to find areas of similarity between the two. For instance, the intestine of a fish is quite long and convoluted, just like a human intestine. I’ve done a couple of dissections myself, and have found that my understanding of anatomy did get better. If you’re looking to do your own dissection, look no further! I’ve listed the steps below. Have fun reading!

STEP 1

Find your fish. I prefer using the Catfish, since it’s quite easy to cut open. Another alternative is Milkfish, though I haven’t used one myself.

STEP 2

Find your instruments. You will need a scalpel, a needle, a scissor and a tweezer. I recommend wearing gloves and a mask. You might want to get some air freshener as well (it gets really smelly, so if you can, do it outdoors).

STEP 3

Using your scalpel, make a light cut on the underbelly of the fish starting from the anterior end. Extend it all the way back towards the posterior end. If your cut isn’t deep enough, go back and do it again. If you widen the gap, you’ll be able to see the internal organs. The first thing you should encounter is the stomach.

STEP 4

After encountering the stomach, you can go ahead and remove it. If you carefully analyse its contents, you might find some digested food (maybe smaller fish). Go ahead and remove the intestines. I did this using the tweezers. Try being gentle, otherwise you may end up breaking it.

STEP 5

Keep exploring. Widen the gap you’ve made and look into the anterior cavity. You can find a very dark red organ- the fish liver.

By this time the cavity should be quite empty. Look inside- there will be a large white structure (you can’t miss it!). It’s pretty rubbery. This is the swim bladder, used by the fish to maintain a specific depth. You’ll have to use your hands to remove this, since it’s attached to the dorsal wall. Now extend you original incision towards the anterior end till you reach the point shown below.

If you’re lucky, you’ll also find the heart (it can be a bit hard to find. I didn’t get it in this dissection, but I did find the heart of a different bony fish I’ve forgotten the name of).

A fish heart is quite different as compared to a human heart- while the latter has four chambers (Right Atrium, Right Ventricle, Left Atrium and Left Ventricle) the fish heart only has two chambers (an upper atrium and lower ventricle). Another interesting fact is that while the human heart has a double circulation system (blood flows in two circuits – from the heart to the lungs and back and from the heart to the body and back), a fish has a single circulation system. In a nutshell, blood follows this pathway – body to heart to gills to body. Blood does not return to the heart a second time.

STEP 6

Onto the eyes and gills. The gills can be a little difficult to remove since they have a flap called Operculum covering them. You can use your hands to access the gills.

An interesting fact about these gills is that they use Counter Current exchange – a mechanism which involves exchange of liquids between two bodies flowing in opposite directions to each other. The capillaries in the gills flows in a direction opposite to that of water, thus creating this very mechanism. Nephrons in the human kidney use a similar mechanism to concentrate urine.

The eye is actually quite interesting. Though I haven’t tried it myself, you can remove most of the slimy layer and obtain the near circular lens of a fish. If you hold it up to a light, you’ll be able to see how light passes through lenses and flips the image upside down.

STEP 7

Clean up. It’s not the best part of the dissection but absolutely necessary. You might want to get rid of the smell too. It helps if you have a cat (I hear they like fish).

Overall, I had a lot of fun doing this dissection. It’s something entertaining as well as educational that one can do in the lockdown. I hope you enjoyed reading this blog post!