from what I can tell if you trade on bittrex binance or other non linked with bank account exchanges then you are fine its only when you send funds into an account (cash out) that the bank recieving will report to IRS. So even coinbase I believe is not the one reporting to the IRS its the individual customers banks receiving the deposits from coinbase when you withdrawl. So as far as I can tell No agency can know your gains for trading because many of the exchanges are not connected to banks
Though if you were to keep such activity hidden and eventually get busted, it might be considered tax fraud.