I remember arapaimag saying for wyckii, their aggression will be as its lead to be in anything under 600 gallons. And I had an artc once, he lived up to his reputation only leaving my leporinus alone due to the fact he couldn't catch him. For a nemurus comfortably I'd say a 180, for a wyckii I'd say a 600, must be if it'll leave other fish alone. But I think a wyckii will be comfortable in a 300g, alone of course, someing like an 8x3x2 to keep a wyckii for life, they aren't skittish, don't have long whiskers, and aren't the most active specimen. If you read back on them, you'll find arapaimags threads,night ve had some on pcf too so just use google lol, he grew one to 24" in a 180, one to 24" in his largest tank, and another to 22" I believe this one started off in his second largest tank and then moved to his largest one. According to the only consistent updates we had on a wyckii was justarn his grew to 18-20" in 2 years, i think that's how long he had it might of just been one year but he got it at 12-14" he said. I've only heard of 2'+ wyckii, never seen proof of one. But I don't doubt some specimens getting there, though I think those have good genes and are exceptionally old specimens.