Very nice!
I believe this species is Trinectes maculata....(AKA Achirus) from South America. Some reports say they start off brackish and ultimately require full marine conditions. Well the fish must be very versatile, I had one for 5 years in fresh water before selling it on, it was 8" long when I let it go.
Whats yours eating? I could only get mine to eat earth worms, it would have eaten small live fish for sure but I prefer not to go down that route where ever possible.