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Japanese Medaka

Japanese Medaka. Mitotic Images Embryonic Development. Stage 1(0 Hours) Oviposition. The unfertilized egg appears opaque. The yolk sphere is surrounded by a thin layer of active cytoplasm. Many small oil droplets are distributed randomly beneath the cytoplasm. Stage 2 (0.2 Hours) Fertilized.

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Japanese Medaka

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  1. Japanese Medaka Mitotic Images Embryonic Development

  2. Stage 1(0 Hours)Oviposition • The unfertilized egg appears opaque. The yolk sphere is surrounded by a thin layer of active cytoplasm. • Many small oil droplets are distributed randomly beneath the cytoplasm.

  3. Stage 2 (0.2 Hours)Fertilized • The yolk is transparent and yellowish in color. • The egg is about twenty minutes old. • The oil droplets have not changed.

  4. Stage 3 (0.8 Hours)Germinal Disc • The active cytoplasm comes together around the zygote nucleus, which results in a cap at the animal pole. • The oil droplets move to the vegetal hemisphere and begin to fuse.

  5. Stage 4 (1.5 Hours)Two Cells • There are fewer oil droplets, which have also enlarged. • The fusing of the droplets continues throughout early development.

  6. Stage 5 (2 Hours)Four Cells • The second cleavage plane is at right angles to the first.

  7. Stage 6 (2.5 Hours)Eight Cells • The third cleavage plane is at right angles to the first.

  8. Stage 7 (3 Hours)Sixteen Cells • The fourth cleavage plane is parallel to the second, resulting in a single layer of cells. • These cells are arranged in two rows of four cells.

  9. Stage 8 (3.5 Hours)Thirty-two Cells • The four central cells of the sixteen-cell embryo have divided tangentially.

  10. Stage 9 (4 Hours)64 Cells • There are two layers of blastomeres surrounded by sixteen outer cells.

  11. Stage 10 (6 Hours)Early High Blastula • The blastoderm consists of five layers. • About thirty outer cells are continuous with the yolk cytoplasmic layer. • The ventral surface of the blastula is essentially flat.

  12. Stage 11 (9 Hours)Late High Blastula • The blastoderm is circular structure comprised of 12 layers, making it about 0.6 mm in diameter.

  13. Stage 12 (12 Hours) Flat Blastula • The blastoderm has flattened and expanded.

  14. Stage 13 (13 Hours)Dorsal Lip Gastrula • A thin crease clearly marks the dorsal lip where involution begins. • The blastoderm diameter is about 0.9mm.

  15. Stage 14 (15 Hours)Embryonic Shield • The gastrula has expanded to cover 3/8 of the yolk sphere. • A broad shield has built up at the dorsal lip. • A narrow germ ring extends laterally from each side of the shield to halfway around the blastoderm.

  16. Stage 15 (17 Hours)Mid Gastrula • The blastoderm has expanded to the equator of the yolk sphere. • The shield length narrows, and the germ ring is no longer visible.

  17. Stage 16 (20 Hours)Late Gastrula • About ¾ of the yolk sphere is covered by the blastoderm. • The shield is slightly more centrally dense where the embryo is developing. • A few large oil droplets are located near the vegetal pole.

  18. Stage 17 (23 Hours)Early Neurula • The central nervous system appears as a streak of cells in the middle of the shield. • A large yolk plug protrudes from the blastopore.

  19. Stage 18 (26 Hours)Late Neurula • The anterior end of the keel has broadened into two divisions of the brain. • The embryo is 1mm in length. • The blastopore shrinks into a small opening.

  20. Stage 19 (29 Hours)Blastopore Closed and Optic Vesicle. • The closure of the blastopore is complete and gastrulation ends. • The tail is forming.

  21. Stage 20 (33 Hours)Anterior Somites • Two to four pairs of somites appear. • The optocoele develops within the optic vessel, still attached to the forebrain. • There are no pigment cells visible on the embryo or the yolk sac. • The size of the embryo has increased.

  22. Stage 21 (36 Hours)Pericardial Cavity and Optic Cup • The pericardial cavity is defined ventral and bilateral to the midbrain and hindbrain. • Early optic cups are formed without a lens. • Three brain divisions are distinguishable. • There are six to eight somites. • The embryo length is about 1.3mm.

  23. Stage 22 (40 Hours)Optic Lens and Otocyst • The optic lens is a small round lens, not filling the cup. • Optic lobes are enlarging and brain ventricles are forming. • A new large cavity appears on the yolk just anterior to the head; gradually it moves forward and fuses to the pericardial cavity.

  24. Stage 23 (46 Hours)Heartbeat • The early heart, a narrow tube entirely ventral to the head, pulsates 40 to 60 times a minute. • Blood islands group on the yolk, but there is no circulation. • The head and tail have began to lift off the yolk sac.

  25. Stage 25 (54 Hours)Body Movement and Otoliths • Anterior somites twitch infrequently and may bend the body axis slightly. • About 22 somites are formed. • Two tiny otoliths are barely perceptible lying against the inner surface of the otocyst. • The tip of the tail is completely lifted from the yolk sac.

  26. Stage 24 (52 Hours)Beginning Circulation • Colorless blood containing few cells, moves slowly through the aortae and vitelline vessels. • The heart beat is strong, and beats about 60 times a minute. • Reddish-brown chromatophores appear in the floor of the brain. • The embryo is about 1.5mm long; there are 19 or 20 somites.

  27. Stage 26 (56 Hours)Retinal Pigmentation • Black granules speckle the optic cup; the retina gradually darkens. • Cardiac contractions have increased to between 100 and 120 per minute.

  28. Stage 27 (62 Hours)Pectoral Fin Bud • The pectoral fin bud appears as a broad swelling posterior to the emerging anterior vitelline artery. • Body movements have increased in frequency and blood circulation is strong. • 26 somites can be counted.

  29. Stage 28 (74 Hours)Pink Blood • The heart is now bent so that the ventricle lies to the right and posterior to the atrial end. • Pink blood is obvious in the heart. • The tail has lengthened the embryo to about 1.7mm. • About 30 somites have developed.

  30. Stage 29 (84 Hours)Vitelline Veins Sinuous • Cardinal and vitelline veins take a sinuous path in lieu of branching. • The pigmented retina can be seen. • The pectoral fin appears thick and bluntly pointed. • The tail may lash and move the whole animal.

  31. Stage 30 (102 Hours)Urinary Bladder • The bladder appears left of the pectoral fin. • A chamber forms the heart ventricle. • The heartbeat is 140 per minute. • Blood is dark pink. • The tip of the tail reaches to the eye.

  32. Stage 31 (121 Hours)Pectoral Fin Movement and Caudal Fin • Weak twitches occur in the pectoral fin. • Caudal fin is developing. • Urinary bladder has a greenish tint. • Cornea is visible, but still touches the lens. • The heart chambers are differentiated. • Blood is reddish in color.

  33. Stage 32 (128 Hours)Liver Rudiment • Colorless liver first appears at the edge of the greenish urinary bladder. • The cornea of the eye may be raised slightly off the lens.

  34. Stage 33 (144 Hours)Swim Bladder • The liver is composed of colorless globules and covers the urinary bladder on the left side of the animal. • The intestines are transparent • The swim bladder now appears as a clear vesicle mesial to the urinary bladder. • The lower jaw is forming. • The heartbeat is 170 per minute

  35. Stage 34 (168 Hours)Jaw Movement and Yellow Coloration • The lower jaw is beginning to twitch very infrequently • There is a yellowish shadow to the dorsal aspect of the head and trunk • The eye may be capable of slight movement, the cornea is well lifted off the lens. • Dorsal fin is present

  36. Stage 35 (200 Hours)Spleen and Mouth • The spleen arises as a small red colored structure between the urinary and swim bladders • The liver is conspicuous • The head begins to straighten out • The mouth has moved upward making it visible, and moves actively • The yolk sac lacks pigment cells and has diminished considerably in size • The embryo thrashes

  37. Stage 36 (264 Hours)Hatching • Those that hatch by the 11th day, have a larger yolk mass • There are about 30 somites • Shortly before hatching the mouth opens • Upon hatching the larvae has coordinated swimming and breathing movements • The swim bladder are is the size of the oil globule • Urinary bladder and spleen are brightly colored. They, with the liver, are located on the left side. • The ventral fin is long and broad and deeply cut by an anal opening. • The abdomen flattens as the swim bladder absorbs the yolk.

  38. Caring for the Young • Medaka larvae begin to feed the following day of hatching • The aquarium must be “baby proofed”, the filters must be shut off to prevent injury and the plants at the bottom of the tank need to be good oxygenators. • The water temperature should be 16-28°C • The fry must be fed protozoa for at least the first 7 days and newly hatched brine shrimp for the next 2 weeks. • Finely chopped white worms and tropical fish food may be fed sparingly to the 3 week old Medaka fry.

  39. Helpful Hints • DO NOT OVERFEED!!! • When fed wisely and not overcrowded, Medaka young grow 15mm in length within 4-6 weeks • They may now be cared for like adults • Newly hatched fry are always in danger of being eaten by older fry • Medakas mature in 2 to 6 months • They have a life span of four or more years

  40. What We Thought About the Lab!! • Jody Manners, Tracy Rhodes, and Alex Smith surveyed 25 people to see what they thought about the Medaka lab. • 76% thoroughly enjoyed the lab • 16% mostly enjoyed the lab • 8% enjoyed only certain parts of the lab

  41. Our Opinion on the Lab Throughout this lab we have learned many things about developing embryos. This experience helped to complete our understanding of this critical topic. Using the laptops and microscopes was very rewarding and helped us learn first hand.

  42. Credits • Alex Smith, Tracy Rhodes, and Jody Manners • Animations from Medakafish Homepage at http://biol1.bio.nagoya-u.ac.jp:8000.html • Clarion University • Karen Anderson, Clarion University • Mrs. Maine • Mrs. Maine’s and Mrs. Wolfgang’s Academic Biology Classes • Pictures from BioG 101-104, http://biog-101-104.bio.cornell.edu/

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