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Just that really. The thing is that we got 'large' ones so they wouldn't be eaten when added to the tank so I don't know how old they were when we got them. Is there such a thing as an average life span?
3-4 years? Nah, they live way longer than that. This is a pretty reliable list of life expectancies. Cardinals aren't on there but neons are and other similar-sized tetras. Really I would expect 5 years at least. 1 year in the wild is probably because they have to share with piranhas