I am sure that it is derived from either animals and/or fish. Although according to Jewish Law you are not suppose to mix meat and dairy, you can mix fish and dairy ("you can't put the calf in the mother's milk"). Plus, I think it is a lot more technical when it comes to using things from animals that are not "meat". As someone said earlier, if it says "kosher gelatin" it really just means that it is not pork based.
Personally, after doing research on Kashrut (kosher law) and vegetarianism, I believe that you cannot really be kosher in today's society and still eat meat (in Judaism it is believed that you have to honor the animals and therefore must kill them in a "humane way" as well as honor their life, and do so as seldom as possible - today's practices and slaughterhouses simply don't do this). I could go on about this for a long time, but I will save it for another thread!