When my two boys were growing up we took many trips out armed with a simple but effective fish bottle trap and indeed it was one of the first articles I did for the now defunct Cub Supplement (April/ May 2011) which used to come with Scouting magazine. The most easily deceived freshwater fish is the humble Minnow. In my experience the two best size bottles are the 2 and 5 litre clear ones. Start by removing any labelling on them.
The next stage is to carefully cut the top of the bottle off at the point where it starts to curve up towards the lid. I find putting the lid on, gently squeezing with the holding hand gives sufficient rigidity to use a bread knife to make a cut of a few inches.
I then use scissors to finish the remaining cutting as it's easier to finish with a straight and clean cutting action.
Once the cutting is complete you will end up with the bottle in 2 pieces as shown above.
The larger bottles will have a handle that will need removing, normally this is possible by bending it back and forth until the plastic fatigues.
The reason that the bottle is cut where it starts to taper is that the top needs to be turned backwards into the larger section (above) and therefore needs to be a snug fit.
With the two parts in situ use a hot skewer (warmed in a flame) to punch four holes through both (where they overlap) equally spaced. This is made easier when the bottles have a square shape to them like the example.
It almost goes without saying that the skewer will get hot and I warmed the one used here on a gas hob ring.
I then use simple food bag ties to secure the two sections together. The advantage with these ties are that when releasing whatever you've caught and changing the bait both are easier.
And here is a shot of the trap with three of the four ties in place. So easy are these to make that this one was made on a family holiday.
You will, of course, need to add some weight to the fish trap and the obvious inclusion is a few stones. I've tended to come away from using stones as I was concerned about damaging anything I caught so I made a 'mat' of metal rods that sits in the base, large fishing weights on a string also work well.
As stated earlier Minnows are so gullible to the point where they seem to accept their lot, even to the point of continuing to eat the bait whilst incarcerated! Some species, such as Perch, seem maddened and try their best to get out inn fact there's a picture of them in the Cub supplement link mentioned earlier.
I've had various species show an interest in the trap with this circled Crayfish being interested in plain bread, and an Eel squeezing in during a holiday usage of the trap. A larger bottle would have seen him go all the way in but his long length meant he didn't have to sadly.
Actually I made the standard fish trap just to get the necessary pictures as it was actually a seaside vacation and this bottle trap was going in the briny. the modifications are as follows: start by cutting the threaded bit of the neck off where it joins the main part of the tapered bit.
Then make several cuts at 90 degrees all the way around the hole, just over an inch in length. Once done splay them out slightly. This gives an aperture that larger crabs can get in.
And as with the standard trap the top part gets put in the main part reversed and secured.
The 5 litre bottle makes quite an ample sized trap.
One modification I've made for harbour fishing is to cut a hole in the middle of the bottle with splayed edges to give any beasties that are lurking in the gaps a chance to enter as the trap is pressed up against the stonework.
Both versions will need some sort of cordage tying to it to make it retrievable with paracord and crab lines being obvious choices. The former is more comfortable to haul a full pot up but the latter has a lot of length in a small area. With a sea version I also put on a small bright object (which in this case is off a flat fish lure) so it can be seen in the murky depths.
Another useful addition to the weight is a small bait box. It secures the bait at the rear and if you are using bits of meat it means that it's kept in one place and therefore makes cleaning easier.
This is the one time you can throw a plastic bottle in the sea with no guilt attached!