According to the contest requirements, I have made an all paper art piece to hang on any wall. It can also be used as a hanging (by not pasting the fish cut out on any sheet) or a design piece to stick on your lampshade from inside to have a fishy light in your room ;)

Had a happy time doing this !

Thanks to this contest and instructables ! :D

Supplies

A3 size sheet - 2
Pen knife
Pencil
Double Sided Tape
A4 size sheet of 4 colors ( color reference in the image)
Fevicol

Step 1: Cutting Out the Fish

Draw a fish from a pencil or you can trace it also
Now by using a pen knife, cut pieces out
For Fins, make a borderline , so that you can take that as margin line and cut thin wavy strips.
Do the same thing for other fins and fish tail.
You can make partitions in fish tail to give it more intricate and defined look as I have given
For the body part, draw double half circles for scales and cut out the inner circle.
At last cut out the fish from the outer margin line.

Step 2: Background Water Effect

Take three shades of sheet and randomly cut wavy circles out of it from smaller to largerin size, like shown in the picture.
Now paste the smallest one on the darkest shade from double sided tape and then lighter shades upon it. To make a little 3D effect or depth.
Finally take a A3 size sheet and cut out a rectangle a bit smaller (take 1cm) than A4. So that the white sheet work as a border for the water depth piece.
At last paste the fish cut out on the top.