All the tax issues and concerns in connection with Bitcoin or any cryptocurrency for that matter are depending on the country where you are a citizen of. Laws varies from one territory to another and there are some countries which still have to officially pronounced on how they gonna collect taxes on their people dealing with Bitcoin and just allowing the normal activities of trading to flourish first. In USA, you are obliged to declare whatever capital gains you earned and I think this is the same thing with trading...it all centered on the tax on income and gains similar to other investment instruments. The best thing to do is to ask someone (maybe an accountant, if you have an access) on the tax laws to make sure that you are not violating any as we know that getting entangled with the tax man can be a big headache. As many are saying, there are two things we can't avoid here in this world: tax and death. So we might as well pay our taxes appropriately and timely while still living and doing some business even if we are into Bitcoin or cryptocurrency.