I think I forgot to share a full body shot of my specimen, I don't think it will be helpful for gender identification but please enjoy it!

Can I ask how big your specimen is? I can't help with sexual dimorphism, though being an Auchenipterid, would it not be similar to other fish of this family where the male has the modified anal fin copulatory organ?
As an aside, @Jools - I noticed the SL for Tocantinsia piresi is 3.9" yet ...

https://www.instagram.com/reel/C3wm-UJrmvU/?utm_source=ig_web_copy_link&igsh=MzRlODBiNWFlZA==

Hi, I'm currently keeping one Tocantinsia piresi for about 3 years and I wonder is there anybody have any idea about how to identify their gender.
Will there any general sexual dimorphysm of this species?