Instinet, a US-based equities broker will on Monday launch a service that waits until a sufficient number of small orders have been gathered together before matching the total order in one block, in an attempt to address the increasing fragmentation of order sizes in “dark pools”.

The move to “aggregate” orders in dark pools comes as the trading business is increasingly grappling with a trend towards smaller order sizes, not merely on the public order books of exchanges but in some dark pools as well.