I had a Cichlid named Big Lips who lived in a big Kimchi jar. She lived 5 years and was the size of my hand. She was the sole survivor. I had about 20 other cichlids, and she systematically eliminated them all: whether by outright murder, incessant chasing to exhaustion, driving them to jump out of the tank, starvation or Machiavellian cannibalism of other lessers. She was the queen. I miss her. She would lay eggs all over the tank. And since there was no male to fertilize them, she'd get frustrated and eat them all.
I could tell when she was frustrated, too. She was mostly calm, and when she got pissed, oh man, do not stick your hand in that tank. I got nipped many times by those sharp little teeth when I was cleaning the tank. I had to buy a longer cleaning siphon, so I didn't have to stick my hand down there anymore.
She looked just like this, except BIG.