In wild caught toroises the risk of pathogens invading unrelated species is a real one but you have to wonder where those pathogens are going to come from in captive born animals.
This idea of not mixing species is a purist one and doesn't have a great deal of merrit.
Mixing species, while not accepted by the control freaks of the tortoise world, is not a problem as long as precautions are taken that amount to nothing more than common sense.
>I have two young Hermann's together, but they are siblings and have always been together. Whether they'll get along as adults is something else, who knows? If you do decide to get another tortoise, there are a few things you need to consider first. One, there is always the possibility that they won't get along, or that one will intimidate the other. Two, you will need to quarantine the new tortoise for at least a month, preferably 3 months or longer, to avoid spreading disease/parasites to the tort you have now. Third, if you mix species, you should be aware that you are risking the loss of your torts. One species may carry pathogens that don't affect it, but are lethal to another species.
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>>You don't need to get another tort to keep yours company, but there's no reason why you can't! Just make sure you have the room for a separate enclosure, in case things don't work out.
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>>Sohni
>>Northern California
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Ed @ Tortoise Keepers
Trying to keep the fun in Chelonian care