The fish rule...

Hi! I put my housing application in an hour ago, and when I was reading thoroughly through the rules to make sure I saw everything, I noticed a particular rule that stood out to me. That being that specifically non-flesh-eating fish are allowed. And I asked some other friends, and one of them said that their rules did not specify that it had to be non-flesh-eating. Is there a particular reason for this? A story behind this? Its just kind of bothering me, especially since they mentioned it twice throughout the whole rule masterscroll when I was applying.

I'm not bothered because I have a flesh-eating fish, I'm just rather curious about it.