Despite its destruction, the island still holds two Heart Pieces, and is one of the recurring destinations of the Ghost Ship. One of the Pieces of Heart can be found in a small indent by flying with the Deku Leaf directly northwest from the small spiral island chunk atop where the Korok rests. The other Heart Piece is given to Link from the Merchant in exchange of the Shop Guru Statue.
The Triforce symbol appears when the six Goddess Pearl-related islands are connected
An ingame screenshot taken in the pirate ship, inside Tetra's quarter. It shows a Triforce on the map.
It has been speculated that Greatfish Isle was the original location of The Wind Waker's supposed third Goddess Pearl dungeon, because it was the home of Jabun, the keeper of Nayru's Pearl. Since the Great Deku Tree safeguarded Farore's Pearl, and the sky dragon Valoo protected Din's Pearl, it only makes sense for the home of Jabun to exist in a temple-bound place so he too can supervise the care and safeguarding of Nayru's Pearl. However, this theory has not been confirmed by Nintendo, and must therefore be taken as mere fan speculation.
The evidence in favor of this is as follows:
There are interviews where the creators say that some dungeons were left out of the final game.
When connected by lines, Dragon Roost Island, Forest Haven, and Greatfish Isle form a large triangle; the three Triangle Isles, when connected by lines, creates a smaller triangle attached to the larger one - the entire image created is that of the Triforce, and the Tower of the Gods exists at the dead center of the symbol. An image of this can be found on the pirate ship, in Tetra's quarter. This adds further evidence to the theory, as both Forest Haven and Dragon Roost Island are home to temples.
Greatfish Isle's German name, Ichthusk, comes from the Greek word, ἰχθύς, meaning "fish".