I used to have a "pair" of jegui. Their personality was bizarre. I wouldn't classify them as aggressive per se. Since they are rheophilic they tend to pick one spot and just sit there, usually under a rock or log. In that regard they were incredibly boring fish.
If another fish swam too close to their spot then they'd dart out and chase them off. They had zero fear of any other fish. They would chase after anything. With that said, they'd completely leave other fish alone unless A. they thought it was food or B. it got too close or C. looked similar to them.
I actually kept the pair together in a 125 gallon tank. The female was maybe 8" and the male over 12". Every couple of hours he would leave his lair and swim around the tank chasing after anything that got too close to him. If he found the female it was on and he'd chase her mercilessly for 5-10 minutes until she found a spot to evade him. He'd then swim back to his lair and just sit there for another couple of hours. It's like he was patrolling his territory every couple of hours, chase off anything he deemed a threat and then went back in hiding.
The female would then sneak back to her spot and just sit there until the male came looking for her again. Oh, and other than the male, she took no **** from any other fish.
I suspect in the wild they hook up just long enough to breed and that's it. It wouldn't surpise me if after fertilizing the eggs the female would chase the male off and tend to the brood herself. That's how much they seemed to despise each other.
In the 2 years I had them the female "colored up" just once. I use the term colored up loosely... very loosely. She developed a bright red patch on the upper, soft portion of her dorsal fin. That was it. No pink bellies, no red streaks on the sides, nothing.
They ate anything including pellets. They were very easy to maintain.