As I mentioned earlier, the Anhinga smashes the catfish on the tree limb until it is dead, or at least stops moving its tail, He then proceeds to turn the fish so that he can swallow it head first. Seems to me that eating a catfish of any size would be a risky proposition in view of their shiny pectoral, and dorsal fins. Looks like a good way to puncture something important internally. In any event, it must be safe as I see lots of Anhingas eating lots of catfish. I'll post an image of this one being swallowed momentarily. This is the limb smashing part.
Nikkor 200-500 VR lens