Aquarist

You can get this once you progress to the Aquarium Exhibit. On the right hand side there is a small tank up against the wall. Buy this ($3000, thanks UBERSILKR0AD for confirming) and then purchase any coral. You only need one for the achievement. Put the coral (found under decorations) in the tank and go about your normal business.



Over time, the coral will reproduce. I used the very first coral in the shop list and it only took one day. The first time additional coral appears, this achievement will unlock. It may take longer with different corals and may even be random.

If you want to continue this to supplement your income or fill your tanks, remember to feed the coral manually or with an auto-feeder.