Another possible factor — pandas are all wild-collected. Put yourself in a panda cory's shoes (fins?):
You're swimming along the bottom of a tropical South American with your school when suddenly you find yourself caught in a collector's seine. You are hauled out of the water and lie flopping on the sand for several minutes while the collector sorts his haul before being dropped in a bucket with 50 of your schoolmates. You are taken to the collector's house, where the bucket is dumped into an empty oil drum, which already contains hundreds of other cories. A few days pass before you are hauled over rutted dirt roads to a holding facility. There, you are dumped into another overcrowded container with thousands of cories. After a week, a net swoops into the water and hauls you and a hundred other cories out of the water. You are dumped into a big plastic bag and stuffed into a cardboard box, then loaded into an airplane's unheated cargo compartment for a several-hour journey to an American wholesaler. Once there, you are dumped into yet another holding tank where you stay for two weeks. Then another net swoops you up and dumps you into another plastic bag. The bag is shoved into another cardboard box, which is loaded into the back of a truck. The truck is on the road for 16 hours, then the box is unloaded at a pet store. You get dumped into an aquarium, where all day long people stare at you and tap on the glass, making terrifying noises. After a week or three, you are once again swooped up in a net and dumped into a plastic bag. You are taken to someone's house in a jostling half-hour car ride. There, you are dumped into another aquarium.
Wild-caught fish have to not only adjust to your tank but also to all the holding tanks they were previously subjected to, many of which likely had significantly less than optimum water quality. They have to learn to eat new foods, and have probably been hungry or near starvation since a few days after their initial capture. They are exposed to pathogens in crowded conditions. They have to try to adjust to constantly changing conditions which are almost entirely unlike those for which they are naturally adapted. It's actually quite shocking that any wild fish survive the process of becoming aquarium residents.
A suggestion: If you don't have complete confidence in your ability to keep fish alive, stick with green (bronze) and peppered cories. The vast majority of these are captive raised and will have an easier time adapting to life in your tank. Additionally, if they should die, you won't have contributed to the decline of fish in the wild.
You're swimming along the bottom of a tropical South American with your school when suddenly you find yourself caught in a collector's seine. You are hauled out of the water and lie flopping on the sand for several minutes while the collector sorts his haul before being dropped in a bucket with 50 of your schoolmates. You are taken to the collector's house, where the bucket is dumped into an empty oil drum, which already contains hundreds of other cories. A few days pass before you are hauled over rutted dirt roads to a holding facility. There, you are dumped into another overcrowded container with thousands of cories. After a week, a net swoops into the water and hauls you and a hundred other cories out of the water. You are dumped into a big plastic bag and stuffed into a cardboard box, then loaded into an airplane's unheated cargo compartment for a several-hour journey to an American wholesaler. Once there, you are dumped into yet another holding tank where you stay for two weeks. Then another net swoops you up and dumps you into another plastic bag. The bag is shoved into another cardboard box, which is loaded into the back of a truck. The truck is on the road for 16 hours, then the box is unloaded at a pet store. You get dumped into an aquarium, where all day long people stare at you and tap on the glass, making terrifying noises. After a week or three, you are once again swooped up in a net and dumped into a plastic bag. You are taken to someone's house in a jostling half-hour car ride. There, you are dumped into another aquarium.
Wild-caught fish have to not only adjust to your tank but also to all the holding tanks they were previously subjected to, many of which likely had significantly less than optimum water quality. They have to learn to eat new foods, and have probably been hungry or near starvation since a few days after their initial capture. They are exposed to pathogens in crowded conditions. They have to try to adjust to constantly changing conditions which are almost entirely unlike those for which they are naturally adapted. It's actually quite shocking that any wild fish survive the process of becoming aquarium residents.
A suggestion: If you don't have complete confidence in your ability to keep fish alive, stick with green (bronze) and peppered cories. The vast majority of these are captive raised and will have an easier time adapting to life in your tank. Additionally, if they should die, you won't have contributed to the decline of fish in the wild.
