Blue-Finned Elephant Tuna

A Blue-Finned Elephant Tuna (エレファント・ホンマグロ) is a large fish that comes from the South Blue and has elephant-like features. It is known as the "jewel of the sea" and it is supposed to be a miracle ingredient for cooking. It is classified as a type "A"; "Big Friendly" creature. It first appeared in Chapter 98 and Episode 51.

History
In the original manga, Sanji bought one, while in the anime, Sanji competed in a contest against another cook, Carmen and won it. Once the Straw Hat Pirates reached Twin Capes Lighthouse and settled down, Sanji prepared the fish for everyone while they were speaking with Crocus in Twin Cape. Usopp and Sanji were paying attention to Nami and Crocus's conversation while, unbeknown to them, Monkey D. Luffy ate up the rest of the fish, including the bones.

Another one has appeared in the Thriller Bark, when Oars, powered by Luffy's shadow demands food to satisfying his hunger, a large bundle of food was provided, including an elephant tuna. While feeding Oars, the zombies realized that it was a salted fish that could kill Oars if he ate it. The zombies got rid of it at the last second.

Another one has made its appearance around Little East Blue, where it was fished up by Luffy, Usopp, and Brook, but was carried off and eaten by a gigantic beetle called Boss.

Trivia

 * It was also seen in the video games Unlimited Adventure and Unlimited Cruise that it could be caught as a fish.
 * According to Luffy, the nose is the best part of the fish to eat.
 * It has been seen later in the Grand Line a few times, including in Water 7.