hi, this really depends on the animal and what i would be trying to do with or to it. Recently we wanted to study how fights get resolves in social groups and how this affects who becomes the top-dog and who gets pushed to the bottom of the social pile.
We started wanting to work with ants, but the species in Ireland are not very good at being kept in the lab as they really need their queen present which makes life very difficult. Some of the ants in America are much happier being taken away from their colony and you can study them easier. Then we wanted to work on the little fruit fly drosophila as we read that you can make them fight – actually they kind of box each other (http://www.youtube.com/watch?v=VCrQabQJiOg). But it turns out they only fight under really specific situations.
So, in the end we found that the common green shore crab that you get all of ireland are really easy to keep in the laboratory, and are really easy to get to fight and they gave us some great results to work with. One of the researchers in my team looked after them and they only needed feeding once every two days, and we filmed them to study their behaviour for about an hour each day for 3 weeks. It was really good fun and we published 3 or maybe even 4 research papers on this work (i cant remember exactly).