Just got finished making my Pelagos factory, pretty fun overall. I've gotten science shipped off back to Nauvis at this point but was very disappointed to learn that the decomposition science pack doesn't actually go into biolabs. I'm not sure if that's an oversight or not, but I wanted to bring it up because it at least seems like one in my mind. The planet itself is behind Gleba, and the science pack is biological in nature (mostly), so it seems a little odd to me that I had to go back to a weaker lab setup just to start actually unlocking the techs. Could also be a dependency I'm missing, but I installed all required dependencies, so I'm not sure. Either way, was a fun mod, I especially like that the fish breeding recipe gets an actual use.

I might have missed that.
A lot of planet mods use a library that does a few things, including automatically adding all science packs to all valid labs.
At some point, I stopped using this library, so I probably forgot to manually add the science pack back.
Since many other planet mods still use it, I simply didn't notice.
I am currently in the process of porting the mod to Factorio version 2.1, so it won't be fixed on 2.0, but I recommend trying the mentioned library:

https://mods.factorio.com/mod/PlanetsLib

It should fix your issue

That did indeed fix it, thanks for the quick reply!