Is that a fish?

No, it is spalted wood.

Spalted wood is wood that had been discoloured by the action of fungal growths.  The hyphae lay down protein barriers to define their territories and discourage other fungi from entering that space.  Wood-turners can deliberately infect wood and culture it to get this desired decorative effect.  In my case it was entirely fortuitous and occurred naturally in a dead woodland tree trunk that I noticed and immediately photographed.

I have zoomed in on an area that reminded me of a reef fish.  Like a cross between a parrot fish and a sunfish.


This is my entry for Ingeborg's Abstract Thursday Challenge on the theme of abstract shapes, AT478