You need to specific as to how the "score board" is to be used (when it is to be displayed and for how long, what it is used for, etc). Showing your attempted code would be very helpful (the more code, the better).

Ok, so you want an actor that displays a text string. So, you need a field in the seal class to be incremented each time a fish is eaten and a method to be called immediately after to change the text image of the actor that displays the new text string representing the current count.

Check out this video