engelens,
You can enable Harvey the eel like you do with any other of the fishes:
1. click on the picture of the eel in the right pane.
2. Look in the left pane and click the "
up" arrow next to "
Number in tank" to increase the number of Zebra Morey eels to one (1). Unlike the fishes, you can have only one (1) Zebra Moray eel.
Let us know if this doesn't work for you.
The eel is back in the cave