The Alien Rifftrax Presents? You mean the Rifftrax for the movie 'Alien'? I don't recall a Rifftrax Presents called 'The Alien'. Furthermore, I thought 'Rifftrax Presents' pieces were by definition ones that were starring guest riffers, not the MKB Three.
Only Kevin and Bill did Alien, way back when they did a few without Mike. Those are under the Rifftrax Presents banner.
It's toxic to humans, but not fish?
The LD50 (amount that kills 50% of the animals) for rats is for eating the material directly.
Since fish live in water it's hard for them to eat the solid material, since it dissolves in water quickly and dilutes. So the toxicity to aquatic life is listed differently. The second MSDS does list an LC50 (concentration that kills 50% of the animals in 4 hours) for fish, but the concentration is pretty high, it would take quite a bit of it in the water to kill the fish. So the first MSDS simply lists it as not toxic to fish.