The Aquarium staff is wondering about their Nautilus exhibit, their Nautiluses are feeling a bit moody lately and not really eating. They're wondering how much do they actually do need to feed them, the vet says twice a day, a diet of deshelled shrimp and fish. However, the guys at a aquarium in Beijing says we should feed the crabs while a website (Don't remember which) suggests that they be fed once a month. There's also some worrying black patches appearing on the shell, is this because they're falling ill or some other reason? They've tried scrubbing the shell gently with a toothbrush but the black patches are still there and a golden powder starting appearing. What is this? Also, we're looking to ID the species (will provide photos later at some point) Any help will be greatly appreciated.