It's not only if you convert your coins to fiat, but also if you gain profit from trading solely crypto versus crypto. Important thing to focus on with regulations being stricter every year, is that while we don't know it, the exchange in question might be sending all our trading information to the government. I haven't paid any tax over my gains at all since I bought my first Bitcoins in 2013, so I gave my local government a while ago a call to ask what their stance is and in what category earnings through crypto fits, and it should be pointed out that I was happily surprised to find out that the tax over my gains sit below 1.5%. Negative aspect of me declaring everything I hold in Bitcoin is that my overall wealth increases significantly in the eyes of the government, where the ~1.4% tax I already pay over my fiat wealth will now result in the government gaining more from me.