Pets are not really common in Cambodia, at least not in the city, although many Westerners here seem to like cats–probably because expats may be alone here and want some kind of company and cats are relatively easy to keep. At least the cats can generally be left at home all day by themselves and won’t frighten the lady who comes to clean the house.
There are a few shops, though, that sell fish for home aquariums. Probably some of the same reasons apply for keeping fish–they are easy to keep and don’t frighten anyone–but they are also especially valued in Chinese culture and many, many people in Cambodia have Chinese heritage.