Requirements:
Have an Angel Fish, Lionfish and Puffer Fish.
Combine the three Stacked Tanks into a Massive Fishtank
Harvest 50 Worm Nests

2 Extra Warehouse Slots, Sunken Castle, 20 Gold Dust
Notes: Each fish comes from a variety of Frozen Fish which are found by fishing in the Aquarium. Worm Nests are a free gift.