You know, I've been thinking about this.... and I honestly don't know what freaked Fuzzy Rat out about being put under the shower or being put in a tub of water. When I ran the sink she would walk down my arm and stick her nose under the tap to take a drink... But she would claw the heck out of me when I took her into the shower or put her into a tub. I think it was more a matter of her feeling a loss of control. Remember this is the same rat that car surfed on the side view mirror of my car on the NJ Turnpike and climbed to the top of tall trees and walked right up to strange dogs and humans... she didn't really do fear much. But in all of those situations she was in control. Same thing with jumping into the lake, she did it entirely on her own.
As she got older and perhaps wiser she did become a lot more conservative and yes perhaps more fearful. As her strength and abilities waned so did her confidence. When she couldn't see as well in the dark she headed back to the car around twilight for example. This might be true of humans as well. I tend to use jack stands or ramps when jacking up a car now, something I never bothered with when I was a young man. We all get more cautious with age.
Still I suppose we all hate or fear losing control. I think it's human nature and it may be true of rats too. There are just so many aspects of rat psychology that no one has studied. For the longest time psychologists have assumed that rats are pretty basic animals with a stimulus - response mind. It hasn't been until recently that we're starting to realize that rats are metacognative just like us. In designing experiments researchers simply haven't found what they weren't looking for.
I remember back in my time, that lots of rats wouldn't "properly" replicate long established experiments, some folks called them "defective" rats. Generally, it was easiest to simply exclude them from the study, chalk them up to experimental error or do a statistical analysis to zero them out for the sake of a good paper. I always suspected that there was more going on because there really were so many "defective" rats that it was hard to simply ignore them.
I think there's a lot of research that needs to be re-done. This time taking into account that rats are intelligent and emotional, social, metacognative animals. A rat that doesn't run in the maze might actually be trying to get to the experimenter to play or it might just be pressing the bar to please the human rather than to get food.
Sadly, when I started out with rats I pretty much bought into the standard model of rat intelligence. I was a psychology major in the 1970's after all. It wasn't until I started actually working with Fuzzy Rat outdoors that my mindset began to change. Nothing she did made any sense. Why would a rat like to climb trees or jump into a lake after her human? Why would she want to go into dangerous places to explore? Why would she enjoy meeting strangers? Why in gawds name would she climb out of a moving car at highway speed? Then when she started trying to communicate with me and started rewarding me when I did something right, I had no choice but to rebuild my own mental construct of a rat's mind to something much more similar to ours. This doesn't mean that 40 years of research is wrong, just that there's a whole lot more to the big picture than was imagined in my day. And I based the framework of immersion theory on rats being intelligent animals, and so far that's worked out pretty well for lots of people and rats. I think rats are motivated by lots of things that aren't just related to fear or rewards.
I know there are a lot of young people here on this forum who's minds aren't as rigid as my own. There's so much more to learn about rats and ourselves. I so encourage every young person here to keep an open mind and imagine the possibilities. Don't let your world be shaped by the misconceptions and narrow thinking of the past. There was only one reason that it took hundreds of years to 'discover' that the world was round... and that was because someone else had already 'proved' that it was flat. Every rat owner has to opportunity to add something new to the big picture... so if your rat is doing something strange, embrace it... your rat is always right, it's a real rat after all, so when what your rat does doesn't fit the model in your mind of what it should do... it's because the model is wrong not the rat.
I do look forward to the kinds of things those of you with young minds are going to discover. It's going to be a lot easier for you to embrace change and new understanding than it is for those of us who were born when the moon was still made of cheese.
Who knows why some rats like to swim and other's don't? But it would be a great project for someone to figure it out.
Best luck.