Assorted Crayfish (Cherax sp.)

Crayfish are basically freshwater lobsters that never got the memo to grow up peacefully — they'll eat, dig, rearrange, and occasionally dismantle anything in the tank that isn't nailed down, including tankmates that get too close. Keep it solo or with genuinely tough, fast fish and it'll reward you with constant, visible activity most true community fish can't match.

Care level: Easy · Temperament: Aggressive · Max size: ~5" · Min tank: 20 gal · Diet: Omnivore, scavenger