I did some searching online for ideas and I kept seeing the wall decal schools of fish. I thought these were cool, but the decals seemed a little too ordinary as I've seen decals used a lot these days.
Fortunately, Heather's husband has a lot of wood working tools and cutting the fish out of wood (as opposed to decals) was a great option (especially since I didn't have to do any of the cutting or sanding). The fish were stained with a gel stain. I have found that gel stain is fairly easy to work with (applied with an old t-shirt rag) and then top coated with a satin clear coat. I was told that gel stain works well for woods that my not take the stain particularly well, which was a concern with the wood that was used. The gel stain worked out just fine for this project.
In order to get a well planned grouping on the wall, I created a paper template for hanging the fish. It enabled me to figure out a grouping and make it easy for us to locate an ideal spot on the wall and hang the fish. I outlined the fish and holes were cut out of the middle of each one on the template to place the 3M hangers. The template worked out particularly well for us because we painted the wall blue after installing the fish the first time. It was great to have the template available for re-hanging the fish.
Hanging them ... The 3M hangers were a good idea. They adhered to the wall nicely, but for some reason, they were not holding on to the back of some of the fish. We ended up having to superglue some of the hangers on the fish. As far as I know they are all still holding up at this point.
Here is a final photo of the room. I think the blue wall is a great compliment to the stained wood fish. The orange lamp also got a facelift with the rope lamp shade, another fun DIY project. See that post here.