Training your fish to do tricks.

[Aqua Nut]

They sell them directly on Amazon http://amzn.to/2glwnsK

 

[Renegade Aquatics]

Surprised no one has mentioned Mormyrids yet, one could argue they are probably the smartest freshwater fish
If I remember correctly they have the biggest brain in comparison to their body of any fish

 

[Thekid]

That's awesome!! Did you find it?

They sell them directly on Amazon http://amzn.to/2glwnsK

The video itself is embedded into a PowerPoint. Here's a crappy screenshot-