embryos fail to mineralize otoliths. (A) DIC images of OVs at st. 30 (dorsal views of the left OV). Grown otoliths are observed in wt OV. Mutant OV contains numerous seeding particles that form a paste-like precipitate (Inset). Red arrows: seeding particles; Asterisks: otoliths. Scale bars: 20 μm. (B) Immunofluorescence of an otolith matrix protein, OMP-1 (dorsal views of the left OV). Anti-Oncorhynchus mykiss (Om) OMP-1 serum is used. In mutant OV, immunoreactive substances cling to the epithelium. Scale bars: 20 μm. (C) Alizarin Red staining for mineralized otolith. Crystal is never observed in mutant OV (dorsal views of the head; white dotted lines show OV). Scale bars: 100 μm. (D) TEM images of the epithelium of the OV at st. 25 when the otolith is forming (the prospective macula region; lateral views). In a wt embryo ‘globules’ coalesce to form the otolith precursor in the posterior end of the OV. In the mutant, by contrast, very fine particles are observed at posterior end of OV (D) and mid-position of the OV (D’). Asterisks: growing otoliths; Black arrows: fine particles; ‘g’:globule; ‘s’:seeding particle. Scale bars: 1 μm. (E) Immunofluorescence of acetylated α-tubulin st. 24− (dorsal views of the left OV). Many short cilia protruded from the epithelium are visible in ha OV as well as wt one. Scale bars: 5 μm.