We use minnows and shrimps pretty regularly. And catch them in a very simple way.
What we use is a atta kneading dish (tasalla). Basically a big dish with 3/4 inch sides. Tie a cloth over the whole thing. Make a small hole in the middle of the cloth. Rub some atta around the hole and stick a large chunk of atta inside the pan.
Then put the entire contraption into the water, sprinkling some dry atta on the surface of the water. come back after 15 mins and take out the contraption fast. You'll find lot of minnows inside.
As for shrimp. I have found nothing better than my old butterfly net. I just dredge the weeds and come up with all sorts of goodies including shrimp.
this works wonders... have made a home made one slightly larger than the atta plate!!! for shrimp and others, use mosquito netting dredged along the bottom near weeds... you'll get a whole bunch of stuff that way...