How do fish know each other??

[lily]

I have posted in other sections about my pond sagas but think here is where I should be posting.
We bought 6 fish few week ago, 3 from the same pond and another 3 who had lived together.
These six soon bonded and they are now all pals and hang around together.
We bought in more fish and the dynamics changed.

I know the fish to look at because we got them all slightly different to look at.
I used to look after ponies who to other people looked identical but I knew apart both by looks and personalities.

I just wonder how fish recognise their pals and strangers ?

And what makes them accept or not other fish?

Do they have a pecking order?

 

[lily]

just to add my beginners observations,
our original fish and the koi are definate pals. The koi seemed to make an effort to join in right away which I mistook for him being a bully. (He seemed to shadow a certain shebumpkin and stick at their side to seperate them from the group.No longer happening)
He is now part of the group. The latest goldfish though slightly bigger has not been accepted as the koi was.
I know nothing about fish but I can see they have a social network.. I just wonder is it by sight or smell or what?
We have changed our minds and have put the latest goldfish into the wildlife pond. We are inexperienced and perhaps should have left him longer but hubby said the whole group were chasing him constantly and so we have put him into the smaller more shallow pool.
Its not permanent but he has lots of plants to weave between and plenty surface cover but the down side is its only 18inches deep. There are lots of bugs in there and we are interested to see if he eats all the bugs. (there are no visible bugs in the water of the fish pond as there are in the wildlife one)
Im hooked on this hobby.

 

[DoDad]

Mine have name tags.:lol:

 

[lily]

do dad you are bad!!!!

I am thinking these fishy guys definately have a gang thing going on!