I had a female pastel that was just flat nasty. She was mean. She didn't hiss, she just bit (and this was pretty much full grown). Little guys though, need to act tough sometimes. Could just be he is having a bad day, or you startled him maybe. Also, maybe there is a shed coming. I have had some of mine be grumpy and hissy, and I didn't know why, then low and behold a few days later they are blue. Don't let the hissing scare you off though, keep handling him as usual.
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