I think it would be really cool if you could send credits to other players.
If you like my idea please leave a comment, if enough people comment I will send off a suggestion to the administrator and see if he could make that possible.
Also check out this Agar.io video! https://www.youtube.com/watch?v=zcCoT3KjoY8
Has been asked in the past. It will not be an option. As you see most credits here are almost free. Maybe in future will add an option to tranfer bought credits only. But for sure transferring free credits will not be an option.