They definitely will bite at night, as others have noted. However, different lakes/rivers seem to have different feeding patterns, and these patterns can change depending on time of year. For example, i've fished lakes when the only time i could get any action was early in the morning, right around sunrise. I'd say most waters have a certain timeframe when the night bite will be particularly active, but a lot of times this might not be until 2:00 or 3:00 am. There have been numerous times when i've quit fishing around 12 or 1 am due to a slow bite, only to wake up in the morning to have others tell me the fish really turned on a couple hours later. Anyway, my point is that it all depends on water, weather, and time of year, but generally carp can be caught just as easily at night.