Stevenator, here's pictures of the fish traps I have built.
They're shaped like heart of a pretty girls butt.
And well.. The "mouth" of the trap is, where you would expect it to be. xD lol. There's even a joke about this, how fist trap maker knows the best shape for it, it is the shape that womans butt leaves on sauna bench.
And its correct! I built mine using fibonacci ratios btw to make it have natural proportions. And the green colour is amazing addition, this makes sure it looks "natural" under water and the colour and all is mimicing water plants which fish use for cover.
Mine has a bunch of features I have copied from other trap makers, basically taking all the best things I can think of and put them all together. Like five handles on top, big wide hatch to release the fish with a sort of hook to keep it closed. There's a bump in the "mouth" at bottom and top which has a straight horizontal ledge on the inside, this fools certain bottom swimmer fish from escaping. The mouth is 105mm wide but its made so that it can widen to around 200mm or approx 8" to allow absolutely huge fish inside, but then it returns to its original shape so that big fish doesn't know how to get out. The fence is 70cm long, twice as long as a normal one, that's from the old fashion way of making these as the ancient ones might have a fence longer than three meters.
If I remember correctly, the trap is 105cm wide and 140cm long counting the fence. Its not the biggest of these things but definitely bigger than a normal one, also its 60cm high, so takes quite lot of space, but its not too hard to manage, number of handles really helps. Maybe on new ones I could add maybe three handles on the sides too just in case those are needed. Another idea would be to have a hatch at the bottom part to even easier let fish out.
These things are perfect for letting unwanted fish go free without harming them. A lot of times they're in perfect health even after day or two, no missing scales. I think a fish trap like this is the most humane way of fishing, they're easy to to use, easy to let unwanted ones back and its very effective! When ever I use five of these in certain spots I know to be good, I can catch so much fish each day I don't know what to do with them and definitely can't eat them all, so few of these allows me to choose which ones I want and never run out of fish. Permits for them are also very cheap so its very good way for catching some lovely fish food.
Most typical ones are perch, pike and ide along with some others.