Your photo seems to best match a Brazilian species called Potamobatrachus trispinus, which is figured in the latest paper on the classification of toadfishes. However, if you do an image search on that species name, you end up with very different fishes, most of which appear to be other freshwater or brackish species. There is extra confusion also because there is another species with the same specific epithet (the second part of a species name): the Indo-Pacific species Batrachomoeus trispinosus. From what I can tell in the paper, Potamobatrachus does not have venomous glands in the dorsal fin or gill cover spines, but I would play it safe just the same. Sorry I couldn't offer a more confident identification (though I am pretty confident), but most of the details used to distinguish the species require microscopic examination of specimens. BTW, I forgot to mention freshwater stonefish as another name used in the aquarium trade ... again confusing because stonefish belong to a different, distantly related family.
Tony