Venustus Acting Erratic

[GABBA]

Hi. This is something I posted on another forum, however to increase my chances of a reply I am also posting it here.

I have a 22cm male Venustus that has always been fairly confident in my 6ft all-male display tank (as he is one of the larger fish). Over the past couple of weeks he has totally changed. He now stays in one corner of the tank, has taken on stressed colours and also has outbursts of flashing and darting around the tank before retreating back to his corner/hiding spot.

All the tank mates I have in there shouldn't be a problem, the only one that may be of an issue is the 19cm Nimbo. Fusco. However since I have added the Fusco I have never noticed him chasing any other fish! I have even watched the tank from a distance (so they can't see me), and there doesn't seem to be any aggression coming from him.

It might also be worth mentioning the Nimbo. Venustus hasn't not eaten in a fair while. I have been consciously watching him during feeding time for about a week now and during this time he has not eaten. I saw him spit food on one occasion but that's it. I don't think it is bloat as I haven't seen any white stringy feces (I had bloat go through my tank a few months ago so I treated all fish with metro).

I don't actually have a hospital tank on hand so it makes this situation a little more difficult. Any ideas/suggestions/comments.

Thanks