http://ncis-source.org/2012/12/18/ncis-behind-the-scenes-of-tonys-apartment-exclusive/
Whose brilliant idea was it to have Tony’s only living companion be a goldfish named after his dead partner? Surprisingly, it was two superfans who came up with the Easter egg! “We had two 13-year-old girls on set one day visiting, and I said, ‘Don’t you think Tony should have a pet?’…and the girls said, ‘Oh, yeah. It’s good if he has someone to talk to.’” explains Weatherly. But as soon as they had landed on an easily maintained pet goldfish, the next challenge was to name it. When the girls came up with “Kate,” it was too perfect to pass up. “So we made it so,” he says.
Episode s10/e10
"You better watch out"
I would have gone one step further and called it 308 the caliber Marine Snipers prefer and are affectionately name "Kate."