1. The most common "doctor fish" is the Blue Tang (Paracanthurus hepatus). This fish is known to pick parasites and dead skin off other fish, giving the impression of a "doctor" tending to patients.
2. Another fish often called "doctor fish" is the Cleaner Wrasse (Labroides dimidiatus). These fish are known for their symbiotic relationship with other fish, where they clean parasites and dead skin in exchange for food.
3. Sometimes, the term "doctor fish" is used more broadly to refer to any fish that has a symbiotic cleaning relationship with other fish, including various species of Wrasse, Gobies, and Shrimp**.
Therefore, the "nickname" depends on the specific fish you are referring to. It is important to be specific when discussing these fish to avoid confusion.