Hi:
A freshwater lionfish is usually the common name for a saltwater sculpin- are you sure its a toadfish?. These live in brackish water marshes, and can tolerate brackishwater for extended periods. It is born and raisied in saltwater, and as such i would treat it as a sw fish and feed it foods enriched for HUFAs.
I would ween this bad boy onto dead prepare marine foods.
frank