Japanese Medaka Journal

by Jocelyn Hughes and Emily Forrest
Day 1
We believe that our egg (Javier) is 26 hours old. A yolk, cytoplasm, vitelline membrane, and what we think are blastomeres (the hairs) are visible. It has a very small blastopore as well, fitting the description for a 26-hour-old medaka egg .
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Day 2
Judging by our picture from day 2, we think our egg is now 33 hours old. There aren't any optic cups or lenses, so it definitely can't be any older than 33 hours. The little hairs that we thought were blastomeres are actually projecting filaments. The large circle that is in the egg is a blastopore.
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Day 3
Little Javier has a very unnoticeable heartbeat. This means he is 46 hours old. He is beginning to get his little eyes. Also his head and tail are beginning to lift off the blastoderm.
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Day 4
Javier has a very fast heartbeat, beating 75 times per minute. We think he is 74 hours old. The tail is becoming longer and the cardinal vein is a wide and flat arc near the center of the yolk. With this heartbeat, we believe that he will hatch sometime around day 13.
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Day 5
A lot happened over the weekend; his heartbeat is now 101 beats per minute. We think that it is 102 hours old at this point. Javier now has a bladder, and the tip of his tail reaches the whole way around to his eye. There is still no pectoral fin movement.
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Day 6
Little Javier is growing so fast! Soon he will be embarrased to be seen with Jocelyn and I. We are just trying to enjoy the baby (egg) stages. Today his heart beat 138 times per minute. We believe he is 108 hours old. He has started to twitch slightly but not continually. The eoptic lenses have formed, the optic lobes are enlarging, and brain vetricles have formed. The auditory capsule is present and the neurocole has extended into the hindbrain and spinal chord. The tail is completely formed and reaches to the top of the eye. Its blood circulation is strong as well, and the pink color is visible.
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Day 7
Today Javier had a heartbeat of 144 beats per minute; this makes him is 132 hours old. He seemed to be twitching a lot more today than usual. His cornea is visible, and all his heart chambers are differentiated. His heart appears to be doubled as well. Javier's urinary bladder is a greenish color and his liver is visibly anterior to it.

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Day 8
Baby Javier is almost ready to hatch. His heartbeat for today was 173 beats per minute making him 156 hours old. The fundamentals of several of Javier's internal organs have developed. His liver is composed of colorless globules and nearly colvers the greenish urinary bladder. The intestine is see through and the swim bladder appears as a clear vesicle mesial to the urinary bladder. Javier's ventran fin has widened (along the entire ventral edge of this tail). Also, his lower jaw seems to be forming.
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Day 9
Our baby boy Javier has finally hatched! He was born sometime between acitivity period and 7th period today. This means a lot happened over the weekend, on Saturday he would've been about 180 hours old and Sunday he would've been around 204 hours old. Today he was around 228 hours old.We had a hard time getting a picture of our little guy, so we got a video (the best that we could). He now has all of his organs and is about 5 millimeters long, but this does not mean he is att his adult stage yet. Before he hatched, his head would've extended and his mouth opened. He was able to swim and breathe right before he got out of his egg and his caudal fin is rounded with the fin rays forming within. Now his ventral fin is longer, broader, and deeply cut by the anal opening, while his dorsal fin extends halfway to his head. While he was hatching, the ventral abdominal contour flattens as yolk absorption proceeds and the swim bladder inflates. Also, yellow chromatophores spread onto the yolk sac. The organs he has now are a tail, liver, heart, eyes, mouth, gills, and urinary bladder. We love you little Javier, have fun in the fish tank with all the other little ones!