Fiat gains: I think to be safe, you should pay taxes on fiat money capital gains in India as well.

Crypto trading gains: I don't think there is any tax treatment for crypto-to-crypto trading gains (not booked in fiat) except in the USA, where the IRS has issued guidelines to tax crypto-to-crypto trades

Taxation can be retrospective (e.g. Vodafone case). Not sure if the government will issue guidelines this tax year. My sense is they will treat Bitcoin as "commodity", so capital gains should be paid on fiat gains but not on crypto gains. They "may" ask people to declare their Bitcoin holdings in tax returns although they have not done that yet for gold, property etc.