Bill,
I have a screen on the intake ( suction ) side of the trash pump, nothing on the discharge side. The holes on the suction side are about 1/4 in diameter. They are too small for a FHM to go thru, but I suppose a GSF fry could be passed thru it, and I pumped from the creek for about 3 months to fill the pond. I bought the fish from Ozark Cat fisheries at the lake of the ozarks. Their reputation is pretty good from what I can tell, they ship fish all over the world according to their website. I don’t like pointing fingers at them without proof, it’s more than likely that I introduced them from the creek, just didn’t think they could survive the impeller of the pump and then go thru 400’ of hose, but that does make sense, again I hate the thought of accusing them, it’s just there was no red on the flaps, and I have been trapping and fishing hard for them, have not seen any???