Both my tanks are covered. I have a dragon fish in the 65gal and he likes to shoot up the side of the tank fast and glide to the other side. I've had an Oscar in the past land on my couch and that was with the lid closed too. I think if you've got a jumper they'll find a way lol. I agree though lids do keep the water from evaporating and also keep the splash from making a mess. However, topless does give the tanks a very sleek and sexy look. Maybe one day with a bigger tank I'll give it a go again.. That's the thing with this hobby you can always change things up 
