I have no idea how big they are (diameter), but the "drink bottle" trick might help you ?
For bigger fish (and a big enough tank) I'd use one of those larger "water cooler" bottles - otherwise you might be able to modify a different sized bottle to suit the length & diameter of your fish...
Cut the top (neck end) off a bottle
Turn it upside down
Re-attach to the rest of the bottle, so that the spout/neck is inside the base (use tape that will stick underwater - don't seal it permanently, as you need to get the top off to let the fish out

)
Put food in bottle
Put bottle in the bottom of the tank, & wait for the fish to eventually swim in through the neck of the bottle - they're not likely to be able to get out quickly so you can just pick the bottle up & move the fish (water in bottle and all)
Repeat as required
If the "drink spout" of the bottle is too narrow, you might be able to cut the spout bit off so that the opening is a bit wider.
My explanation might not be very good, but hopefully you might understand what I'm trying to explain
