I have to confess, I didn't do enough research - and what I said about Mercurochrome being banned here, is not correct. It's still readily available from the discount chemists mobs.
It IS banned in Switzerland, Brazil, France, Germany, and the United States - but not here. At least, not yet.
Apparently, Mercurochrome is effective as a disinfectant, not only because of its skin-drying effect - but also because even the tiniest amounts of Mercury (or its unstable compounds) disinfects, by disrupting the metabolism of microorganisms.
In other words, it kills bugs - very quickly, and very effectively.
I suspect there's a lot more to it, but because Mercurochrome has been around for so long, and because no-one has ever studied its antiseptic operations in depth - nor done any major research on it, as the USFDA insist should be done, it doesn't seem likely we'll ever get any scholarly articles on Mercurochromes antiseptic actions, effects, or long-term toxicity.
As the basic chemical (Merbromin, or more correctly, dibromohydroxymercurifluorescein) is watered-down in a big way (2mg/L, or 2% - meaning you're actually buying 98% water, in a bottle of Mercurochrome!) - and a little bottle of it goes a long way - I can't see where it rates as a "toxic" compound, as the USFDA insists it is. There's probably substantially more mercury in your imported fish, from polluted 3rd world countries waterways and oceans.