If you're using broadcasts, the issue is because since all clones respond to broadcasts, they will also clone themselves. A simple fix to this would be to make a variable, for this sprite only, like this:

(clone?)

and we can use to to make sure only clones do the cloning, like this:

when green flag clicked
set [clone? v] to (0)
... // your other green flag stuff

when I start as a clone
set [clone? v] to (1)
... // other clone code

when i receive [buy fish v] 
if <(clone?) = (0)> then
... // buying fish code here

This works because if you have a variable “for this sprite only” each clone and the mainsprite can have it set to different values, so each clone will have it as “1” and the main sprite will have it as “0”. Hope this helps!