Aeration helps improve the gas exchange so you get more oxygen (O2
) into the water and more carbon dioxide (CO2
) out of the water. If you have a large water body with a big surface area (length x width), you get good gas exchange. A small surface area will have a poor gas exchange.
Depending on the number of fish in the water and how big they are, will determine on how much surface turbulence you need for the gas exchange. A couple of baby guppies in a 20 litre (5 gallon) tank probably won't need any aeration but 100 baby guppies will.
Don't use breeding cages/ traps. They stress the female and make her more likely to have problems giving birth or eating the babies.
If you want to get the highest number of babies surviving, have the female in a decent sized container (40 litres plus) with lots of plants and feed her well. She will be relaxed and comfortable and less likely to eat the babies. Most guppies don't eat their young any way but having lots of plants and feeding the mother well reduces the risk even more.
And don't move heavily gravid (pregnant) fish because you can stress them or harm the adult and or babies. If you have the females in a tank with males, move the males out and leave the females where they are.