I have TWO red-finned sharks; they definitely have human characteristics! They are the MOST ACTIVE fish in the tank. The first month, one definitely bullied the other. Every hiding place the timid one found, the bully took it over. After several interventions from a nervous Betta and some carefully added hiding places, they began to get along. Now, one peeks around items...trying to get the other's attention. Taunting, you could say. They engage in a quick chase, (similar to hide-and-seek). Eventually, they retreat to the largest hiding spot, cuddle, and clean the Raphael Catfish. This love/hate relationship has been going on for over a year. I rarely watch television any more...this underwater soap opera is far more entertaining.
I have a red-finned shark in my 200 L tank. He has his own cave. He prefers it to living under the log, which is where he lived before I added the cave. He is kind of territorial. He chases the other fish out of his cave (understandably, it is HIS cave :). He doesn't hurt them though. He cleans the plants for me (not too thoroughly though). Apparently, different sharks have different personalities. I've noticed many differences posted.
I have 2 Red-Finned sharks in a 200 L community tank. I have had these for about 8 months now...and they are most definitely active members of the community. The larger of the two (around 10 cm) occasionally chases the smaller one (around 9 cm) for a minute then loses interest. I thought he was being a bully...so I separated the two by putting one in the 75 L. I watched for 3 days as they totally "stressed out" (they turn light grey), as an experiment I put them back together in the 200 L...within minutes they were happily chasing each other again and their color was black again. :) At night they like to lay down on the gravel together (about 8 cm apart). They never bother anyone else in the tank except for the occasional fin "cleaning" of the other fish.
I have noticed that in larger (150+ liters) and very well planted tanks they are much less likely to hide. Plastic plants do not have the same effect on behavior, no matter how many you have.
I have a rainbow shark in my 140 L tank and he is probably the most communal of all my fish. He is almost black in colour, with a creamy belly and very bright red fins. He seems very happy in my tank. These fish never seem to stop eating. If he's not eating the frozen bloodworms, he's eating algae or wafers and most of the time his belly is quite large. He is very active and never stops moving. I'm able to feed him out of my hand and he follows my finger around the glass. He is about 4 months old and he has doubled in size to about 13 cm. I recommend this fish to anyone.
My rainbow shark likes to sleep upside down in his cave. Sometimes when he feels a little dominant he might chase around the giant danios I have in the tank. Other than that he is very peaceful and likes to spend his time eating. He is a wonderful fish and I love him!!