Nilsfish,
Is it a cowfish or a trunkfish? The latter is perhaps more of an issue in regards to toxicity, but my experience has been, once acclimated, the toxicity of trunkfish is minimal. However, the downside is, if you ask people how long their Ostracid (cowfish or boxfish) lived, the answer is very often less than a year - for a number of reasons, none of which I've ever been able to resolve.
Jay