Base of the caudal/ tail fin of the Perch (Perca fluviatilis). Image appears a bit soft due to the epidermal mucus covering the skin.

- Image ID: T8T33G
Erkki Makkonen / Alamy Stock Photo
Image ID: T8T33G
Base of the caudal/ tail fin of the Perch (Perca fluviatilis). Image appears a bit soft due to the epidermal mucus covering the skin. Scanned from film.