The swimming activity of Atlantic herring larvae, Clupea harengus L., was assessed on the last days of a laboratory-based study in Kristineberg (Sweden) in 2013. The direct interaction effect of temperature and CO2 was tested at low food conditions over 32 days in four treatments resulting from the crossed design of two temperatures, 10 vs. 12°C, and two CO2 levels, ambient 400 vs. elevated 900 µatm pCO2. The data set was used to analyse activity of larval herring under the impact of realistic end-of-the-century CO2 concentrations at two different temperatures under low food conditions.