An automatic fish feeder. The pushing and pulling motion is achieved by this Bluetooth smart fingerbot https://www.amazon.com/dp/B0B97G3B8G?ref=ppx_yo2ov_dt_b_product_details&th=1

Put the puller in the tray of the container, connect the fingerbot to the end notch, then stick the fingerbot to the container. Put food in the container. When the puller is pushed out, some food will be dispensed.

Depending on your printer and material, you need to play with the scaling of the puller or sand it a lot to get the proper size for pushing and puling.