Hi !
In Hannover museum I have seen the Blind Cave Fish - very nice

and need no light, good for enery saving

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I think your Cherax papuanus catched the fishes, because they are big and seems to be a delicious meal - very small fishes or small shrimp gonna be ignored for bigger Predators. So I also have to take care, that while growing my cryfish not like to eat his tankmates. But when the Cherax is grown up he gonna ignore the small tankmates. Imorptant is to have always a close look how the crayfish behaves and if it's not working to have the ability to move it to another tank.
Also I keep an grown up Macrobrachium pilimanus together with Bumblebee Shrimp. This small shrimps stay most time at the wood and swimming flowers and the Macrobrachium ignores them. He like to eat his easy to catch Fish food ... But bigger Fish or shrimp, he gonna try to catch for sure.