We are an aquaculture facility which occassionally has an outbreak of hydroids in our systems. We are looking into using fenbendazole as a treatment as it has proven to be very effective eradicating these pests. The fenbendazole is dissolved in a small amount of DMSO and added to the system. My question is how does the fenbendazole break down in the system or does it? The systems are closed recirculating and large water exchanges are not feasible. We do have UV sterilization that is shut off during treatment and I would imagine that once on, the UV itself would degrade the chemical but I need to know for sure. While the fenbendazole is not toxic to the organisms we are rearing, at the dose we are using, it is at a slightly higher concentration. So having a residual concentration of fenbendazole in the systems could be disasterous over time. Using case study that shows it is out of a cows' system after 13 days doesn't work with aquaculture because of the constant exposure of the organism to it's environment. Any input is much appreciated.