Dolphins can't be fed any kind of fish, or lead the player to treasure

Dolphins cannot be fed raw cod, salmon, or tropical fish, and therefore can't lead the player to treasure. This also makes the achievement "echolocation" impossible to obtain. 

 

Expected result: Dolphins can be right-clicked with a raw fish to feed them and will then lead the player to a treasure such as an underwater ruin.

Actual result: Nothing happens when right-clicking a dolphin with fish (will not be fed).