Bitcoin and cryptocurrencies (or cryptoassets) are relatively new concepts for governments and their taxmen. Each country has different regulations around this topic, so the best idea for you would be to consult someone who is well-informed locally and knows your country's specific rules. Generally, in most countries around the world, profit made from Bitcoin investments is treated similar to any other profit and is taxable.
Taking United Kingdom as an example, you only need to pay taxes when you sell your Bitcoin and make profit out of it. Bitcoin investments are treated as assets and fall under Capital Gains Tax (unless you trade cryptocurrencies as a business in which case it will be treated as Income Tax). Regulatory landscape around crypto moves rapidly, so don't take our word for it: you can read more about UK taxes fro cryptoassets here: https://www.gov.uk/government/publications/tax-on-cryptoassets/cryptoassets-for-individuals