Hi..

You make me think about keeping one of our European eels.
Having tried, I'd advice against that. They'll eat any
other fish in the tank which they suspect will fit in
their mouth, they'll rearrange anthing in the tank that's
not physically bolted down (not kidding - my 50cm eel
pushed around rocks the size of footballs; every morning
the tank was completely rearranged), it's an escape
artist, and yes, it's nocturnal.

What an eel! It must have studied interior design and sport
at the GSU (Gulf Stream University). :-)

Possibly a buddy for my pond mussels?

There's plenty of interesting european fishes to keep in
aquaria

Of course, I did.

--
cu
Marco