Fish traps are all pretty similar in theory. Each one has a holding space and an entrance usually equipped with some sort of barbs or other form of exiting resistance. A fish will enter the trap at the entrance hole. This point becomes narrower and narrower until the fish must squeeze through the opening into the holding space. After the fish enters the trap it will be unable to escape because it is one thing to swim past the barbs, but another thing entirely to swim against it. It is trapped.
I like this design because it is easy to carry, super cheap and easy, has a large holding space, and the lid is interchangeable depending on the fish you are after (i.e. catfish or crayfish).
Step 1: Parts and Tools
This is what I used to make the bucket trap; it is by no means an absolutely necessary list of materials. Feel free to shake things up. Don't have a drill? Use a nail and a hammer, you get the idea. All of these things can be found at your local hardware store, and are very cheap. You shouldn't have to spend more than $5 - $10 for this project.
Step 2: Prepare the Bucket and Lid
I drilled holes in the bottom of the bucket to allow water flow, but not so big that any fish or cray fish could escape. Then I prepared the lid by cutting a 9.5" hole in the top with a dremel and a cutting wheel. After the hole was cut out I attached the lid to the bucket and drilled holes around the inner perimeter. The holes will be used to secure hardware cloth to the lid.
Step 3: Cut and Attach Hardware Cloth
Cut the hardware cloth according to the size of the opening in your lid. A little math will come in handy here. Measure the diameter of the hole, mine is 9.5 inches. Now calculate the circumference of the hole with pi! The circumference equals diameter * π. In this case 9.5" (diameter) * π (3.14) = 29.85". This will be the length of the hardware cloth, and it's ok to round up to the closest .5" (or .25" if your using 1/4" cloth). I cut mine at 30".
Cut down the cloth between 6 and 12 inches. Then cut across the cloth making sure you leave loose barbs attached to the piece you will be using. The side with loose barbs will be used in the access hole.
Roll the piece up and connect one section with zip ties. Then attach the entire piece to the lid, again with zip ties. I used a total of 30 zip ties around the lid. This may be over kill, but it was so easy and quick I thought why not?
To make the fish access hole you will need to roll the cloth together at the barbed end. It's a little tough to do this without a little prep work. I cut the cloth down it's length so that there were a total of four sections. After doing this I was able to roll it all together, again, secure the pieces and any openings with hardware cloth. Make sure the hole isn't too small so that the fish you are after can't fit in, but not so big that it can escape. At this time take care to cut any wires to make barbs facing the bottom of the bucket.
Step 4: Go Fishing!
I'm not sure if setting traps can be considered going fishing, but I'm using it anyways. Use bait that will attract your desired species of fish. I'm after catfish so I put some chicken livers (clearance chicken livers at that) in the bottom of the bucket. Find a good spot for your trap and set it. Let it sit there for a day, and with some luck you will have caught some fish.
Some things to consider. First, find a spot that isn't obvious, not for the fish, for those who might come across it. Believe it or not people will steal your trap (I know, this happened to me). Second, make sure you can retrieve your trap easily. Secure your trap with cord to a permanent structure like a dock, tree, or heavy stone. Third, add some weight to your bucket with stones or other heavy objects to keep it at the bottom of the river or lake. Fourth, know your local laws. This trap might be too big to use, you may need a fishing license (pretty cheap), you may need to attach a tag to the line with your info on it. Point being, make sure you aren't doing anything worthy of a fine from fish and game.