It only degrades in extended UV light.
It biodegrades in about 500 years instead of the 100,000 years like ABS.
That's off the top of the memory, could be way different numbers.
Another advantage of PLA is that it's non toxic to people and animals.
I would think that is important for little tiny livers in fish.
Never personally heard of aquaponics issues, might be something with dilution, salt water, pH, etc.
But most tupperware storage containers are PLA last time I checked.