These three pictures (two behind the fold) feature, apart from gudgeons, a small turbot. See if you can spot the turbot in the first picture.
Spot the turbot! © Ice Swimmer, all rights reserved. Click for full size.
In the second picture, the turbot is decloaking.
I’m here! © Ice Swimmer, all rights reserved. Click for full size.
In the third one, it’s gone back into hiding.
I’m not here. You aren’t seeing me. © Ice Swimmer, all rights reserved. Click for full size.
The brackish waters in the saltier parts of the Gulf of Finland and the Gulf of Bothnia are on the limit for the turbot. They cannot procreate in the low-salinity waters far from the central basin of the Baltic sea.
OK, I must admit I do not see the turbot in the first and third pictures. Either its mimicry is excellent or it is not there.
Charly @ 1
There is a third explanation.
I couldn’t see it in the first picture, but I can in the third, it’s not as well covered in gravel.
Jazzlet gave us the third explanation. I’m not actually sure, where exactly is the turbot in the first (but it is there), looking for eyes should give one a clue.
If one is a prey species for turbot and a bit paranoid, the gravel is full of eyes.