SepH deficient larvae are prone to oxidative stress. (A) Fluorescent detection of H2O2 (PF2 fluorescence) in WT and seph mutant larvae at 5 dpf. (Scale bar: 200 µm.) (B) Quantification of H2O2 in WT and seph mutant larvae at 5 dpf. n = 5. **P < 0.01. (C) Morphological assessment of WT and seph mutant larvae exposed to menadione (1 µM) from 3 to 5 dpf. (Scale bar: 200 µm.) (D) Quantification of phenotype (unaffected, moderate, or severe) observed following menadione (1 µM) exposure from 3 to 5 dpf. Moderately affected larvae include minor defects, such as edema and tail curling, whereas severely affected larvae include major defects, such as widespread tissue necrosis (loss of transparency).