immediately_preceded_by developmental stage Medaka stage 30 Medaka stage 31 Gill blood vessel formation stage OlatDv:0000340 Zoological Science 11: 825-839 (1994) - 3 days 23 hrs Stage 31 (3 days 23 hrs) Gill blood vessel formation stage: Large cells of the hatching enzyme gland migrate up to the region under the central part of the eye, which now has a cornea. Blood circulation is seen in the gill arches. Pigmentation of the melanophores in the choroidea proceeds as a dark network in the eye. The pronephric kidney appears as a bright structure adjacent to the 1st somite. The transparent, colorless gallbladder first appears at the posterior region of the liver. Four transparent, membranous protrusions (the structures of the internal ear) are recognized in the otic vesicles. The anterior region of the oral cavity is formed. The tail has 21 somites and a membranous fin which is wider on the ventral side. - 3 days 23 hrs medaka_ontology