what causes this?

[3m]

have looked through several threads and have found nothing like this.looks like his tail is rotting away.
readings as follows:
Ammonia-0
Nitrite-0
Nitrate-0
Ph-8.2
Temp-79 to 81
Salinity 1.024

 

[lion_crazz]

Are there any other fish in the tank possibly biting at it?
What are you feeding this fish?
How long have you had it?

 

[beth]

Lion is correct. That is harrassement.

 

[3m]

Mysis Shrimp
Prime Reef Flakes
Tetra Marine Granules
Brine Shrimp Plus
right now i have the four stripe, 2 rather small Yellowtail Damselfish and one blue damsel the blue is the biggest of the four but is also the one that hides the most. the yellowtails are too small and the four stripe seems to be the big dog so to speak. mind you its a 75 gal tanks with approx 80 lbs of live rock. so there is plenty of room to roam/hide. I've had the fish for about a month

 

[lion_crazz]

Yep, looks like harrassment/aggression to me then. Damsels are a territorial and nasty fish.

 

[3m]

wow thats a shocker as the 4 stripe seems to be the most aggressive of the bunch and the rest all seem to be rather dosile. guess when the lights go out its another story