I encountered something similar to this a long time ago in NYC. My friend who keeps tropical fish invited me to tag along with him shopping for interesting new

I encountered something similar to this a long time ago in NYC. My friend who keeps tropical fish invited me to tag along with him shopping for interesting new additions to his tank. We visited a couple in Chinatown that were striking similar to your Czech restaurant: employees kind of surprised to see someone come in the door, one operational fish tank with one or two fish in it amidst a large wall of empty tanks, comically outrageous over the top nobody-would-ever-pay-that-ever-ever prices. Figured it must have been some flavor of money laundering, but it also seemed... too obvious?