As requested by Aifos:
Barrel eye fish (also known as spook fish) grow to be about 15cm (~6 inches). The green lenses are their eyes, and they are capable of looking straight up through their protective membrane in order to spot food and predators!
If you would like your fish featured, please leave an image link in the comments and let me know their names and species! I’ll then look up a cool fish fact and post it here as a thank you for sharing your awesome friendo!!!