|This is the culprit aka Killer Goldfish|
Sadly my bully Goldfish turn out to be a killer Goldfish. I thought he had a beef only with BlackMoors but since Black Moor is gone he had started focusing on those two poor Orandas. To make it worse I had no idea. I was little bit busy with work so had less time to check them frequently (Usually I check several times a day)
I found bigger Oranda dead next day and I couldn't figure what had happened to him. There were no wounds or anything So I didn't suspected it's this killer guy. And next day I found other Oranda on surface with a huge wound which look like a combo of several biting. I separated the poor guy but didn't make to to next day.
I should have separated these guys when I noticed the bullying first time. I didn't move Orandas to other tank because I thought they are too weak for that one which had no air pump right now. Anyway too late for that now and lesson learned in hard way. :(
I have no idea what made him do it. Now there's no chance of putting him with other Goldfish so he will have to live as a loner rest of his life. I might have to give him to someone who just want to keep one fish many in a 10 gallon tank. I wonder if he would be aggressive toward other fish too. Not Cichlid who would have him for breakfast. other fish like plates or mollies.
Here's a photo of Oranda which died from wounds.