Well I just started and have one female that just had a litter of three and her an babies and the dad are in on big tank and I handle all five of them every day checking on babies, putting in food mom will come to smell me and get pet dad will let me pet him if I catch him other wise he runs alot. Those are my blue dumbos. My blue head male is getting better i can pet him but not pick him up. My black hooded male lucky is the biggest male I have and hell walk to my hand when it's in the tank he likes to get picked up and interact. I handle in what ever way the rats let me once a day when checking on them mainly, momma and the pups get checked normaly every other day I've been doing it and noone seems to mind it. Some of my males have nibbled on my fingers but that's never hurt and momma did a jumping lung like bite where she got my finger on like day four of the babies haha she hasn't since tho.