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I've got an male L027, about 20cm with it's tailfin...
Is it possible for you people out there to give me a location on this, according to the pattern?

It's a (aka L190) rather than one of the Brazilian L027, and they are found in Venezuela and Colombia. They are commonly mislabelled since they look fairly similar.

What makes you think it's a male? Your fish is probably on the verge of growing odontodes, in my experience this can start at about 18cm and anything above this. But both male and female are known to grow odontodes. It probably needs to grow to 30cm for all it's gender characteristics to show, given their adult size.

I thoght, that on L190 juveniles, a rather large part of the tailfin was "white"?
I've had this since it was about 10cm, and it has never had any white on the tail....

Yes they do, but this is a common feature in juvenile Panaque. The white (or 'window') in the caudal fin reduces as the fish grows and the caudal fin becomes a solid colour (black/dark brown). It's perfectly normal for this window to have gone by 10cm, some fish retain it for longer.

But the best way to differentiate between and any of the (aka the L027's) is their teeth. Panaque nigrolineatus have a tight V shape layout and fewer larger teeth whereas Panaque cf. armbrusteri have a wider V layout with many smaller teeth. Check the pictures of the mouth in clog links above.

I've learned that their body color and eye differences really help distinguishing them from each other.

The tail window and teeth is also a good indicator but its a little bit more difficult if you don't want to get them out of the water.

Specially for those monsters out there