I would guess this didn't happen. Mostly because the volume of FW needed to offset waste prodcution of a large bull wouldn't be more than the size talked about here. Also, oxygen levels would need to be addressed. In FW bulls need much higher DO levels to thrive compared to typical FW fish that can live in a pond (most FW bulls are found in rivers that move rapidly). Yes, you can find them in low DO SW, and for short times in low FW - but those are not extended times by any means.
Permitting to collect a bull is one thing and has it's own hoops to jump. Transport is an animal few have been able to take on with any sucess at all. Probably less than 10 crews in the US have done it well. (Bulls are one of the hardest sharks I've ever had to deal with in a controlled setting.) Then to get it eating in a marine environment, and acclimated to FW - this is a massive undertaking that is running before walking.
Proper steps: Keep marine large scale (tens of thousands of gallons). Keep marine benthic sharks. Keep ORV sharks. Keep harder ORV sharks. Then take on a bull in a SW set up. THEN look at lower salinity keeping.