Table 2.

Main characteristics of studied specimens defining each developmental stage

Sample name	Developmental stage	Main morphological characteristics
T1	Big yolk plug	The formation of large yolk plug:
		About 32 h after fertilization, the embryo develops into yolk plug period: blastopore endodermal cells are still externally exposed at the vegetal pole, formation of a large yolk plug inserted in the germ ring, at this time the animal is very bright yellow and the plant polar pigmentation is very deep.
T2	Wide neural plate	Obvious wide neural plate divided into both internal and external parts: about 45 h after fertilization, there is apparition of an obvious wide neural plate; around the neural plate in the head region, there is a clear shaped horseshoe formation; the neural plate grows longitudinally and is divided into inner and outer parts; in the center of the neural plate grows a longitudinal neural groove.
T22	64-day-old fish with electrical receptors ganglion	Fully developed bone plate, 14–16 dorsal spines, 45–47 lateral bone plates, 7–9 abdominal bone plates. Presence of ampullary organs on the ventral face