Great story indeed. Ad it turned out well, too. At my work we use the MS222 indeed to sedate or kill fish (mind you, I'm working with carp at the largest). Taking the dosage up a step at the time is indeed the most safe way to go but with such big fish you're indeed in 'uncharted territory'. Weren't there any zoo-specialist that could recommend anything? I know that in Holland Arapaima have been moved between zoo's (approx. transport distance 150 kilometer). Anyway, nice job and good luck with the tank!