I had a 5g betta tank next to mine and sure enough, one night i noticed the fish was watching.....Stingrays are honestly the worst for being overly nosey and erm... inapropriate times
Had a tank running along the foot of the bed with juvenile motoro stingray in it and her favourite was to sit with her eyes peering over the lip at the bottom of the tank...just....watching....intently.... its very creepy!