Gibbs rule number 45 Always clean up your mess.
Tony mentions he has two goldfish. In 11.1 Whiskey Tango Foxtrot, Tony had one goldfish, Kate. The new goldfish could be Ziva.
This is Ellie Bishop's first case working with NCIS. Gibbs gives her a bullet proof vest with a bullet hole in it. He did the same thing with Ziva by giving her a ball cap with 2 bullet holes when she worked on her first case as liaison officer with NCIS. The ball cap was Tony's, and it's safe to assume the vest was Kate's from when she protected Gibbs.
Its stated above that the cap given to Ziva was Kate's, it was actually Tony's. He shot his favorite cap and Kate shot her non backed up Palm Pilot during shooting practice with Gibbs in Marine Down (2003). The vest could be Kate's as its the same area she was shot saving Gibbs life in Twilight (2005) before Ari killed her.