Diversify!
You may need to do extra training, but the effort will be worth it as it expands the range of work options available during the week and makes for greater security when subjects go out of 'demand' or funding is scarce. I started off teaching music appreciation, but re-trained to teach IT and then again to train other teachers. I also occasionally teach philosophy (something I learned as part of my degree, but also out of interest). Seriously, I am writing this not to show-off but to indicate how one can build up a career out of interests and new training.
Don't forget also that your hobby could also be one of your taught subjects. Usually hobbyists know their subject back-to-front, and so are some of the best committed and enthusiastic teachers. You don't formally need to be qualified in a subject to teach it: but you DO need to know it very well for both you and your students to feel confident in your ability!
Copyright Bob Groves 26/12/2000