On your usual hiking trail you may find a lot of animal tracks but trackways of fish would be very unusual. Fish belong in water anyway. And fish trails in water are short-lived unless they are left in the sediment by animals swimming close to the sediment surface. Then, the fish fin can leave a sinusoidal wave like a snake on land would do. Can you imagine that such wavy patterns at the bottom of a river could be preserved for over 400 million years? That's what scientists think they have found in a sandstone formation in Southwest Wales.
This discovery of Devonian trails include trackways of fish and arthropods. Did the fish fed on those arthropods? A Devonian ecosystem is coming alive!
Source of details and suggestions for further reading:
Geology Today, Vol.22 (No.2), March-April 2006.