Fish attacked?

Question
Good morning Tom,
We have inherited a pond (approx 10ft x 5ft x 4-5ft deep) with some coy carp (1 is approx 18inces long, the other 7 are approx half his size). When we feed them the bigger fish seems quite vicious towards the others.
This morning we found one of the smaller fish lying dead in the garden around 5-6ft away from the pond but she didn't have a single mark on her. Surely if a cat or another animal had got her there would have been marks or she would have been attacked in some way. Would it be possible that the bigger fish could have attacked her and somehow flipped her out of the water?
Thanks in anticipation, Darren Robb

Answer
Hi Darren,

Koi are like their cousins, the Goldfish, and are rarely aggressive or territorial. However, they don't know their own strength and can be extremely boisterous when competing for food. The larger koi is top of the hierachy but it is unlikely he outwardly show aggression towards other fish.

I think the jump was borne out of irritation rather than a fight. If it is a parasite then I doubt it will be confined to one particular fish. Check the pond to see if the others are 'flashing' off hard surfaces and performing tight, unnatural turns. I'd sway towards an outbreak of gill flukes. If you still have the dead fish then lift one of it's gill covers and check for small white parasites living in there.

Catch on of the other fish (preferably the weakest/ smallest one in the pond) and check for excess mucous on the body. This would indicate a skin parasite.

any probs or any questions then don't hesitate to give me a shout.

Good luck

Tom