I found this cute fishbowl printable at First-School Preschool Activities and Crafts and decided to make a math game out of it. I printed out the fishbowl in black and white onto cardstock, colored it with a ble colored pencil, and laminated it with clear contact paper.
I used the addition and subtraction activity cards from this Cookie Math post along with dollar store fish/seahorse/turtle erasers with my 4 year old. You could easily do this with fish crackers too.
She had some fun with this activity: