Sedentary is kind of misleading with this fish species a lot of them are very inactive during the day but each individual is different. Almost all the ones I've had a very active at night out and about hunting for food so I feel they should have a tank that matches the size if each individual fish. I get lots of questions that people want me to answer that I cannot. I have five tanks of these fish and each one is different. These fish are nocturnal with excellent eyesight and very active when the lights are out. My 20 inch male is solo in a 240 he will come out to eat and hang out with or without the lights. He will sit at the top and eat krill or worms as I drop them in. He's much more active at night he will hunt and eat hundreds of rosy reds in one night. He not at all as inactive as he appears to be in the daytime. My 18 inch male is solo in a 125 extremely nocturnal you will almost never see this fish in the daytime, but he too is very active at night and will comb through every inch of his tank hunting ghost shrimp and small fish. This guy needs a new tank soon he is close to maxing this tank out in my opinion. His brother is only 10 inches in a 125 and is always out and active. As soon as you walk by he shoots up to the top looking for food. This male would actually be fine in a 75 for years or maybe his whole life. He is very active in the day or night. This tank also has three females in the 7-9 inch range and they are all active in the day and night as well. My big female 17 inches and is always out active and ready to eat. She is not bothered by light and is also active at night. My youngest male is 14-15 inches he will hang out with or without the lights on will eat in the day but also loves to hunt at night like my other big males. My three big males are very aggressive they don't tolerate tank mates very well. They all prefer live food and love to hunt.