Is he fighting?

[IssueFish]

Hello everyone,

I have just registered with the site but already wonder if anyone can help, please. I have a coldwater tank with 1 pearlskin, 1 lemon goldfish, 3 shubunkins and 1 ghost koi. Ernest, the Koi is in there because he was rescued from my sons failing outdoor pond (the last of 12). All the fish get on well and as they are not huge live in a 120 ltr tank. My problem is, Ed, the largest shubunkin, keeps following Ernest the koi who is larger than him and appears to be nibbling him. Ernest never retaliates and when he moves away Ed follows him. I can stop Ed by going to the tank and he then behaves. Does anyone know why he has suddenly started doing this? Sorry for such a long question.

Thanks
Issiefish (you may notice I entered username wrong on registration-not much good at this forum business)

[~firefly~]

First of all, welcome to the AC.

120 litres is barely big enough for one standard goldfish, let alone the number you have, with koi!

Sorry, but before you analyse anything else you need a tank at least four or five times bigger in my opinion.

[madagascariensis]

I would check if the goldfish is actually causing any damage to the koi.
If not, I would not be too worried. goldfish are fairly smart for fish and if the koi is new it may be curiosity or some "initiation rite" only the fish will know of.
that tank may function temporarily, but likely not in the long term.
your pearlscale may get to 5 inches in length (not too bad)
but your lemon goldfish(I assume that its a yellow common goldfish)
and each of your shubunkins has the potential to reach a foot in length.
the koi, depending on the variety, can eventually top out at close to 3 feet.