Talk to the hiring manager about how you cope and manage in a highly stressful work environment. You can talk a bit about what you do in your personal life to create a healthy balance.
"My work environment is stressful, however; I am able to create a healthy balance for myself through taking time for stress management outside of the workplace. I workout regularly, read books and spend time with friends in casual settings such as patio pints in the sun! All of these things help me to create a balance so that I can easily handle the stress that comes with being a Stock Broker."