Your friend is some what correct once mature snakeheads can only be kept as a solo fish or breeding pair. However , to get a breeding pair you need to start with a group of juvies and let them grow out together, they pair young typically while too young to sex, and competition/ death matches seem to be required for proper pairing. Even if sexed putting 2 fish together typically ends in a blood bath when mature . So really the options are start with just one , or start with a group and hope you get a pair (often they don't pair and u end up with a solo fish any way , no guarantees with channa)