Common Name: Mouth Growths in Longfin Clowns
Scientific Name: Unknown
LongfinClownfish (Amphiprionocellaris) are a variety of clownfish that is commonly grown in captivity. As a result of the breeding process this fish is more susceptible to have mouth tumors. Fish with an untreated mouth tumors become weak as a result of a significant reduction in their ability to eat. Untreated growths can eventually kill the animal as a result of starvation.
More growth images:
Common Opinion: BAD
The solution for his problem requires surgical removal of the growth and antibiotic treatment to reduce infection post operation.
This will not prevent the lump from growing back but will help the fish eat and live comfortably.
Here is a video of such a surgical procedure: