Broker makes significant investment in single stock and program trading.
Goldman Sachs FICC business has seen the biggest drop of all the Wall Street banks so far in the second quarter.
Move could see hundreds of jobs leave London.
Both Citi and JP Morgan cite low volatility as cause of falling markets revenue.
Mike Paliotta, who led the global equities business at the Swiss bank since 2016, has been replaced by Mike Stewart.
Markets business grows despite relative lack of volatility and low interest rates.
Latest hire will bring JP Morgan European equities specialist to US.
Banks across the Street have recently made huge investments into their European electronic trading teams with a string of hirings.
Citi has promoted Amit Raja to the role, following the departure of Fred Jallot to Nomura in April.
Robert Smolen joins Citi from JP Morgan where he headed up the index correlation and hybrid trading books.