i need a mean fish

It all depends on what exactly the OP is looking for. Pretty much any CA/SA cichlid with a mouth big enough will inhale a ghost shrimp. Only problem with that is that most sp. will grow to large for a 30 gallon tank... On the other hand my spotted gar tears them to shreds! (he wouldnt fit in a 30 gallon either)
 
I have a small (2-3") figure 8 puffer, and it attacked one of my bamboo shrimp that was at least as long as the puffer is. Was being the key word - puffer 1 - bamboo shrimp RIP.
 
I could better answer the question, if I knew exactly what you are after? Could you offer a bit more than, you don't want a boring tank? Do you have a reference that we can work with that defines boring to you please?

If fish eatting flakes are boring, there are plenty of other foods to feed, that all fish enjoy. If you want a live-feeder as someone else suggested, your tank will be very limited in its inhabitants - is this a concern? There are other fish types as well, such as bottom feeders, etc.

...but on the surface my concern would be that you might become bored regardless of the feeding habits...
 
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