The fighters, who are fighting in a WBC Lightweight title eliminator, both weighed 134.5lbs and thus were well within the divisional limit of 135lbs.
For Arakawa this is slightly lighter than he has been in recent fights and is actually his lightest since August 2012 when he weighed in at 134.25lbs to defend the OPBF Lightweight title against Takehiro Shimada. Saying that however Arakawa is a natural Lightweight and has always been between 133lbs and 138lbs so likely won't have needed to do any differently to normal.
Linares, who started his career at Super Bantamweight, came in at his lightest since May 2011, when he was 132.5lbs to fight Adrian Verdugo. As with Arakawa however it's hard to imagine he struggled with the weight despite looking tremendous on the scales.
(Photo courtesy of Golden Boy Promotions)