the marking look like damaged fins that grew back at one point
black pigmentation is often damage caused by external parasites.
The fish you have is a wild Lapradei.
It's pretty much certain that all wild Bichirs cary internal and or external parasites.
And pretty much guaranteed to have bichir worm.
This is very easy to treat with meds such as Jungle.
The black markings will disappear over time after medication and good water.
Each of my Lapradeis have black spots here and there. I believe it's simply inherent to the species. My smaller Lapradei has been in my tank for five years or more and the spots have never faded or diminished in any way.