Rat Tail / Bringing a new mate home?

Question
I've noticed lately my rat's tail size keeps changing in girth one day it will be a little thick to the point it looks plump then a few days later it's thinner, he doesn't seem in pain at all and is moving about happily! But something I'd like to know he's a little over two years old.

Also on another note we lost his brother a few weeks ago, sadly and I am taking him in for a check up this Saturday just to make sure he's completely healthy! But he seems sad and lonely he's being much more snuggle-able and he normally isn't but since his  brother isn't here I think he just wants that love/contact more! I wanted to find another cage mate for him, hopefully find one around his age but was wondering how do I go about introducing him? I feel very nervous about that. I have two extra cages so housing isn't a issue just not sure how to let them get to know each other !

Answer
Hi Moni,
A change in the thickness of the tail from day to day seems like it might be based on fluid levels in the body. You can test to see if your rat is dehydrated by gently pulling up the skin over his back and letting it go.  The skin should fall back in place quickly.  If the skin returns slowly, or feels stiff, then your rat is dehydrated.  The slower it goes back, the more dehydrated your rat is.  

A rat who is badly dehydrated will probably need fluids given under the the skin with a syringe.  Your vet can show you how to do this.  If your rat is only mildly dehydrated, you can encourage fluid intake by offering juice or other yummy fluids, or hand feeding your rat fluids.

You'll find instructions for introducing a new rat on my website at www.ratfanclub.org on the Rat Info page.
Deb