I use a home made fish trap. I take a water bottle and cut the lid end off. I turn that part into the bottle to make a funnel. Use some packing tape to hold it together. Put some fish food inside the bottle. Place bottle in tank and let fill with water until it sits on the bottom of the tank. Wait for fish to discover the food and swim in. Then just pick the bottle up, remove the funnel part, and your fish are ready to go into another tank. If I have a lot of fish to catch I usually have to do this once or twice a day. After a few get caught they get scared and will not go into the bottle. Take it out and try again the next day. They forget quickly and will swim in again.