To be honest, these fish make more sense kept in marine tanks. I've seen nice specimens kept with things like panther groupers and morays. They're not the most attractive things to put in a marine tank, but I suppose they have a certain charm.
Another option might be keeping them with the brackish water garpike. They come from the same habitat and get along very well. Lepisosteus oculatus does well in brackish water (SG 1.005 to 1.010). I've seen them around mangroves in Florida feeding on small mullet. At university, I kept both these species along with some young Arius shark catfish in a 200 gallon tank and it looked pretty cool.
Cheers,
Neale