Origami Ghost Knifefish

Ghost knifefish is common in aquarium trade. First time seeing it was on public aquarium in my hometown around 15 years ago. The way they move omni-directionally by undulating their anal fin captivated me.

Image source: fisharoma

This model was designed for Origami-Dan design contest, whose theme was "a design that can be folded in 15 minutes using 15 cm kami". I had sudden idea to design it while having dinner, and then proceeded to finish it that night.

Design and Fold

The subject is very simple. It should be recognizable as long it has head, pectoral fins, anal fin along the body's underside, and color changed tail.

The front part requires at least 3 flaps. One for head, and the other two for pectoral fins. The tail part just need one flap. So an obvious layout is diagonal symmetry. Something like a kite base.

I grabbed a random paper and start folding. This is the layout plan:

Where did the references came from? Well it was just randomly chosen. I made an angle bisector from bottom to top right, and then started from there. The corners on the sides are actually useless. They are folded underneath. So it makes no difference if it was cut off. From now on I will just remove it in the crease pattern so it's easier to observe.

Same result with corners removed.

We need stripes on the tail. Making color changed stripes reminded me of tiger model. Usually a tiger model would need open seam on top, so the stripes can originate from there. However on this model the open seam is underneath. Do we need to perform twist? Not necessarily. An easy solution is to pleat and unwrap. This is what I used on Bali myna wings. 

Given that we now have the seam on top, creating another stripes is easy. Just pleat and swivel the layer to expose the color underneath. It is shown on the final CP.

Next is the head. An obvious solution for head part is bird base, but I didn't use it because it will either create flaps that are too long, has pointy head, or the transition to the body would be messy. The goal is to have seamless body all the way to the head, only separated by gill cover. I resorted in free folding. First to make the head less pointy, perform a reverse fold. Then swivel it to make pectoral fins.

Top: reverse fold along the paper edge.
Bottom: swivel fold to make a corner in the place directed for pectoral fin.

The corner that was planned for pectoral fins are ended up used as gill cover. The pectoral fins were folded from reverse folding the layer under that gill cover. The remaining paper in the end of head is folded inside, and then outside to make lower jaw.

There is one final part: the anal fin. It can be made by a simple pleat.

Once the test fold show promising result, I proceed to use 15 cm kami to fold it. I didn't cut the corners and the paper got really thick in the anal fin near the tail. Nonetheless it is a very simple and teachable models. It can be folded under 15 minutes.