In the first game, the player can choose only three out of eight available species (because the Narwhal, Spectacled Porpoise, and Amazon River Dolphin do not appear in the first game) to have as partners. The first partner the player can obtain is a Bottlenose Dolphin that had somehow become separated from its pod and became confused, because its echolocation was befuddled by the shallow waters of the Lagoon and Coral Forest. The player helps get it to deeper waters and thus gains its trust, meaning that the player will always have at least one dolphin partner all throughout the game.
To befriend dolphins in the first game, the player must simply find the dolphin they want to befriend (any individual of the species, anyway), and learn as much about it as they can (unlocking each of the three information slots) and then continue to behave as if they are still learning about it; that is, continue to feed it, pet it, use the sea whistle on it as much as possible until, when they return to the boat, Catherine will note that a dolphin has come to the back deck of the boat to see the player, at which point the player can choose if they want to keep the dolphin, and, if they do indeed keep the dolphin as their partner, a name for their new friend.
The dolphins in the first game can also learn tricks, but not as specific or as easy to train as they are in the second game. They player can train these tricks by using the Sea Whistle off of the back dock of the Gabbiano.
In Endless Ocean: Blue World, the player can befriend a total of eleven species. However, unlike in the first game, the player cannot befriend just any specimen, and instead must follow specific steps in order to befriend certain individuals from each species, every one of which has certain defining morphological aspects:
- A Short-Beaked Common Dolphin, with a golden tail. This is the first dolphin you befriend.
- A Spectacled Porpoise . This is the second dolphin you receive in the regular story, found in the Iceberg Cavern. It will be befriended after you rescue it from being lost.
- An albino Bottlenose Dolphin. You will befriend it after rescuing it from a Tiger Shark.
- A red tusked Narwhal. You will befriend it after letting Oceana comfort it.
- A Beluga Whale with flower markings. After comforting it by playing your sea whistle at it, you will befriend it.
- A completely pink Amazon River Dolphin. It will be befriended after letting it play with your Narwhal.
- A Risso' Dolphin. It will be befriended after feeding it squid meat and the seafood set that you buy from Nancy
- A Pacific White-Sided Dolphin with different fins. It is easily scared and after a few tries to comfort it, it will befriend you.
- A False Killer Whale with an X shaped scar on its head. It has been hurt by a ship and is easily frightened. After chasing it around, it will become less frightened and befriend you.
- A small Orca . Hayako has seen this Orca before and it loves floating things. After buying a float toy from Nancy, it will befriend you.
- A Commerson's Dolphin with a different pattern on its body that will make you give offerings to the Pacifica Treasure. After giving it all the offerings (they all can be bought from Nancy), it will befriend you.
Tricks (Endless Ocean 2)
Your dolphins will learn six tricks, and some can be upgraded into better and more complex tricks after leveling up. To train these tricks, call your dolphin partner to you using the Dolphin Bell on Nineball Island.
Level One Tricks
All dolphins learn the same tricks at level one:
Jump/flip - Your dolphin jumps in the air.
Sing - Your dolphin sings a song.
Backflip - Your dolphin does a small backflip.
Wave - Your dolphin wiggles its fins at you while floating sideways, which makes it appear to be waving.
Spin Jump - Your dolphin does a vertical jump.
Tail Walk - Your dolphin does a tail walk.
Level Two Tricks
All dolphins learn the same tricks at level two:
Advanced Jump/Flip - Your dolphin does a larger jump, while flipping faster.
Sing - Your dolphin sings a different song than the level one song.
Advanced Backflip - Your dolphin performs a bigger backflip, while flipping faster.
Wave - Nothing changes with the wave trick.
High Spin Jump - Your dolphin does a higher spin jump, while spinning faster.
Tail Walk - Nothing changes with the tail walk.
Level Three Tricks
Some tricks may be replaced by a special trick. These are the defaults:
Super Jump/Flip - Your dolphin does an even larger jump, while flipping even faster.
Sing - Your dolphin sings a different song.
Super Backflip - Your dolphin performs an even larger backflip, while flipping even faster.
Wave - Nothing changes.
Corkscrew - Your dolphin performs an even higher spin jump, while spinning rapidly.
Tail Walk - No changes.