Questioning if my "male" is actually a "female"

[Jenny D]

So I have two boys that I recently put together, after a long process of introducing them. Now they are happily together but recently I noticed Boozer (the youngest) has gained a bit of weight. I do not have a scale, but just visually I can tell. So I began to check my options, I ruled out the treat factor, because I do not give them many treats. Occasionally here and there but no more than 1 a week. Their pellets and hay have stayed the same continuously as well. When searching other threads, I came across a couple accidental sexing incidents and I became worried. I am a fairly new owner (since May 2012), so I thought I would turn to more experienced chin owners/breeders for advice. Unfortunately I cannot post a picture at this time of the genitalia, but as soon as I can I will. I admitt I do find it difficult determining the sex myself because I have seen so many pictures and it is hard to determine on my own chin! I have absolutely no intention on breeding so if boozer does prove to be pregnant I am completely worried! Is it common for chinchillas to gain weight rapidly? Also if this helps, Puffy the older one is for sure a male because I have seen his testicles and full erect penis, when he gets a little "wild" once in a while during playtime, but I have not seen either on Boozer. Please help!:cry3:
Thank you!

 

[Dreamlite]

Without a picture there isn't much we can do but guess. How old is he? It may be possible its a late growth spurt. What color? Some colors grow slower. When you look at the one you know is a male, there is a gap between his cone and his anus, if the other chin does not have a gap it is a female.

 

[ArmyWife]

You should be able to look at the male and then see if your other chinchilla looks very similar. For me, it's pretty easy to tell them apart since the male has the gap between the cone and anus. You need to determine asap if he's a male or female because you're going to have to separate them if that's the case.