No, he's saying you shouldn't have a shark that can't move very much in your tank. If you have a true marbled cat shark, a 265 would do well, with a 180 possibly working. Stingrays are a different story. I personally do not think they need as big of tanks as is said. I currently own one in a 150, and they reach a maximum TL of 16". So it can easily turn around, and also I have 3/4 of the sanded open. As far as I've seen, once they're comfortable they stay buried a lot, and really only come out for a short "stroll" lol or to eat.