Sedge (~3.5+ inches now, male) has always been fairly gentle (I've had him about a year now). He tries to bite if he is being man-handled out of the water or something, but usually if I put my hands in the water, he likes to hitch a ride on my hand with his foot and stuff. He seemed perfectly happy for my hand(s) to be in the water. I don't hand feed him too often, but occasionally when he gets a dried mealworm treat or something I do. He has nipped at my fingers before, but had seemed to learn that my hands were not food, and for the most part didn't bite them.
In the past week or two, I have noticed he is biting much more readily while in the water ... and hard! Last week I was messing around in his tank, and he grabbed the skin on my palm and tried to tear it! This was not an accidental nip- more like trying to see if he could rip a chunk off. It left a mark, but no blood. Then, when I was siphoning water from his tank today, he bit my finger while I wasn't looking, which startled me so I dropped the tubing.
After the siphoning / water change today, I tried hand feeding him a couple treats, because he's a pig and I figured I wanted to keep a positive association with my fingers. He did OK with taking the treats, but I left my hand in there to see what he would do, and he bit one fingers while my hand was in a fist- enough to draw blood.
A few potentially stressful things have happened recently:
Last night I had a bunch of people over. Since he is in the living area, there were a lot of people in view of his tank. He didn't hide or anything and stayed active, but I imagine that caused him some stress.
I recently changed from an in tank filter to a canister filter, and today when I did a partial water change I removed the internal filter (had run both for about 10 days or so). So that was another change.
He also often tries to scratch / rub his shell on hard objects in the tank, apparently to help shed / scratch his scutes. Sometimes I pick him up and rub on his shell a bit to help get some flaky pieces off...he doesn't like it, but he makes a big racket ramming himself into hard things in the tank, so I feel like I want to help speed up that process. Maybe it's making him more leery of me.
Anyway, I know as he gets bigger his bites will pack more of a punch. And I assume he got stressed out this week because of a variety of things.
I'm wondering if he is biting more because he is stressed out / less trusting of me (on the other hand, he has become much more comfortable basking over time, which seems to have the opposite indication), because he is just getting older and perhaps his personality is changing as he grows, or (and I'm hoping it's not this one) he is big enough that he thinks he can actually bite through my skin and eat my fingers like they are fish :-O
I think I'm just posting this for moral support. I'm more confused by the seemingly sudden increase in biting that the biting itself. But it would be nice if he wasn't just going to keep getting more aggressive (or human-eating haha)...
My plan is to leave him alone for a week and then see if he behaves any differently if I put my hand in there. Might as well experiment before he gets big enough where it's a lot more painful...