I have a 4 gallon small tank and a larger 15 gallon tank.
In the smaller tank I have a couple of guppies, a sailfin catfish and a male fighter. I have kept this combination of fish before without any problems, I have also had a fighter, catfish and angel in a similar tank.
However, I went away over the weekend and came back to find the tank absolutely fine, the weekend feeder block had done its job and I rewarded them with some blood worms. My fighter was perfectly happy. They have been in the tank for a month prior to today, and were absolutely fine last night. But this morning I couldn't see my betta, and then I found him huddled up against the heater. His fins were almost completely stripped and although he was breathing he wasn't moving much.
I haven't noticed any major issues before except that the catfish will chase him away from an ornament he likes to hide in. The betta has plenty of other places to hide and one of the reasons I loved him was that he normally chose a floating jellyfish ornament my GF got him and he would sit in the top and spin around. I have also noticed that one of my guppy's tail is split, though I attributed this to my plastic plant and the fact that guppies can get a bit scruffy.
But overnight, my fighter has been mauled, I am tempted to move the catfish into my other tank, at least temporarily.
Problem is, I don't want him to start attacking the fish in that tank who are a bit newer and still settling in. That tank has a couple of dwarf gouramis, black widows and guppies as well as a bulldog pleco (small).
I don't want to move the fighter if it is still alive as the shock might kill it outright, and to be honest I'm not convinced he will survive long enough for someone to answer this. Which hurts me deeply.
The tanks are clean and well cared for, all the levels are bang on. There is plenty of oxygen in the water and the pump pushes the water above the surface to increase the amount of oxygen, but reduce the current for the benefit of the betta. It is due a water change today, I normally do it on saturday but I was on holiday, and I have been doing it weekly while it is new.
I want to know a) whether it is likely the catfish which attacked him, b) what I should do to try and keep him (and the guppies) alive and c) what I should do with the catfish if it was him. Can I calm him down by separating him for a while, or will he need to be returned to the shop.
Incase you worried - The idea was always to move the catfish into the bigger tank eventually. He was in the smaller tank when we got it so don't say its unfair to keep him in a small tank. I was going to replace him with a couple of Sterbas corys.