Urgent my Squareback Anthias lost his tail

my Squareback Anthias lost half of his tail this morning, he looks pretty bad, i had him about four monthes, he acted weired few days ago,this morning i found he almost lost half of his tail, he is hiding in the rock, hard to get a good pic, anyone have any idea whats going on? i love him, he is so pretty, i dont want to lose him

 

what other fish are in the tank

 

Last time my clown got stuck in the filter intake and it lost its tail, but later it could grow back... Yours might be in a fight or a something... bless..

 

He might be getting bullied. Is there a way you can get a close up for fin rot? How are the other anthias? Has he exhibited this behavior before? are any other fish exhibiting this behavior? Is he normally the shy one?

 

That almost looks more than an aggressive nipping. If it once was, it look like it's turn into an infection.

Is he eating?

 

thanks,he still eating yestday, but not today, he is staying same spot for few hours, his tail is pretty bad

 

i never see this before,all the other fish in the tank looks very good,the femal i had her in the same time looks good too,she stay with him sometimes

 

i got few pic, i fed some mysis shimp.he came out for few min,i have 4 yellow tang, a purple tang, a naso blonde tang, a blue hippo tang, a sailfin tang,mystery wrasse, pair clown, pair Squareback Anthias and few tiny goby, im very confused what cause the anthias lost his tail

 

Man how big is your tank. With all those tangs in there I hope its at least 125 gallons.

 

265 gallons , 90 gallons sump, 75 gallons refugum