A teenager is being questioned by gardai after three men were injured during violent scenes at one of the country's oldest horse fairs.
Two people were shot and a third sliced with a slash hook during the Smithfield fair in inner-city Dublin earlier this month.
The 17-year-old was arrested in Dundalk on Sunday and is being held at Store Street Garda Station under Section 30 of the Offences Against the State Act.
Dublin Lord Mayor Gerry Breen claimed the market attracts criminality and has urged government ministers and the Attorney General to shut it down.
One man has been charged with possession of a gun in connection with the March 6 incident.
Animal welfare groups also claim the fair is used to buy and sell horses in poor condition on the cheap when owners can no longer afford to keep them.
Dublin City Council has examined options for shutting the centuries-old Smithfield market but has been told it does not have the power to legally close it.
The Lord Mayor has asked the Attorney General Marie Whelan to use her role as guardian of the public interest to ask a judge for a temporary closure order while new legislation is drawn up to shut the inner city fair for good.
The Irish Horse Welfare Trust has called on the Government to regulate and find a new venue for the Smithfield fair.