Thermal preference assay (28.5 °C vs 37.5 °C) with the 5HT 2B antagonist LY266097. All AS1-treated fish significantly prefer the 37.5 °C half of the arena, regardless of whether LY266097 was co-applied. All conditions that did not receive AS1 significantly chose the 28.5 °C side. At no concentration did LY266097 influence AS1-induced attraction towards noxious heat. N = 58 larvae for the DMSO condition, 57 for 1 μM LY266097, 50 for 5 μM LY266097, 50 for 10 μM LY266097, 59 for 5 μM AS1, 61 for 1 μM LY266097 + 5 μM AS1, 59 for the 5 μM LY266097 + 5 μM AS1, and 56 for the 10 μM LY266097 + 5 μM AS1. Two-way ANOVA with Tukey’s multiple comparisons test used for B–F.