amazing how many fish have a big black spot on their tail...

[Magnum Man]

3 different species in my South American Tetra tank... 2-3 in my African Tetra tank... 4-5 in my barb tank... I'm sure it's a camo thing with the eyes, but it must be highly effective, as it seems many different species picked it up...

 

[CassCats]

It mimics an eye, so predators can be confused over which side of the fish is the front, leaving them unsure of which direction their prey may flee to.

 

[FranciscoB]

If one add fish that have one black spot somewhere, then you have a high fraction of all fish, in part for the reason stated above.
I don’t know if the numbers/proportions are comparable, but a similar argument can be made about butterflies.

 

[Back in the fold]

Very interesting .

 

[Fishfunn]

3 different species in my South American Tetra tank... 2-3 in my African Tetra tank... 4-5 in my barb tank... I'm sure it's a camo thing with the eyes, but it must be highly effective, as it seems many different species picked it up...

My Denison barbs have two yellow spots on their tail, and I noticed that small fry would get fooled and think its another fry. The spots on the tail seem to lure the fry out, then the barbs will eat them. So I thought the spots were more of a decoy to lure prey as well.

 

[gwand]

Danio erythromicron or emerald dwarf raspora have a dark spot on their tail.

 

[GaryE]

Head and tail light tetras are one of my favourite versions.

 

[CassCats]

Hyphessobrycon elachys are my favourites with it, but they're also my absolute favourite tetra.

 

[Magnum Man]

I'm seeing spots... (a Crossocheilus reticulatus convention ) in my barb tank