When I first saw this fish, I thought it was a dried leaf floating in the water. After a double-take, I walked back and realized it was a very stressed fish. I suspect it was feeding crabs before the day was out. It was 20% larger than my hand and having trouble maintaining vertical orientation in the water. I raised cichlids and gouramis in high school, and this reminds me of a young piebald Midas Cichlid (but it doesn’t seem bulky enough). The older breeding males have a pronounced hump on their head. They are freshwater fish, so the salt was likely killing it. They are found in equatorial waters, so it wasn’t the heat. We have schools of fish swimming through the marina at all hours, so it wasn’t a dead zone issue. It looks like someone dumped an aquarium.
Any better ideas on the identification?