in my part of Tx which is just a mile or so from Caddo lake we have Gambusia minnow most everywhere there is a pothole of water in the bottom land. Easy to gather them up using a large dip net. like a fine screen pole net used in bass boats to net a caught fish. Just drag it through the pot hole will come up with gams and crawfish.
No gams out here where the west begins. Last year I was not able to find a source and the local USDA office had never heard of them.
