1) A few koi are seen ‘mouthing’ the pond surface near the walls. But no food is visible, what are they doing??

I put this one up as it is a great example as why we really need to know koi behavior in order to see problems early and also not to act or react too soon!

So when koi ALL rise to the surface and are 'mouthing the surface' in general you always need to think ' gills!' This can be seen along with OTHER symptoms of distress. Clapped fins, wobbling swimming, odd movements and lethargy.

But in my question-- a FEW koi are mouthing the surface at a specific location-- the ways.

It could be algae and that would be the end of that behavior lesson--- the lesson being that koi love to browse!

My question is a little more mysterious! They seem to eating something 'invisible'! And they are and it is!! When you feed fish a bit too often or when the temps are not right for the mix you are feeding, the system builds with DOCs. And these Dissolved Organic Carbons/Compounds are air loving molecules-- meaning they are attracted to the surface and settle/float in density around the walls of the pond. Now koi have better 'smelling devices' than Bloodhounds! The barbels lead them to smells. The oils and proteins of DOC are detectable to a creature that must forage in greens and mud for the slightest bit of protein (live dead or decayed). So the fish 'mouth and suck in' the surface water that is coated at the surface with good smells.

Koi your koi and its behavior will help the traumatized beginner ( from previous bouts with parasites and gill infections) from over reacting to this behavior--

remember

1) Are all my koi doing this?

2) What other symptoms do I see?

3) Are fish interesting in feeding?

4) Do my water testings check out o.k.?

5) Did I do anything different lately? new fish, new water changes etc

6) Are my fish just being 'carp'?