The Medaka Lab!!!!! Woo Hoo!

Mark Cruz
IB Biology II
February 11, 2003
Mrs. Walck

Introduction

	The Japanese medaka are oviparous freshwater killfish.  The medaka is common in rice paddies, feeding mostly on mosquito larvae.  Often, the medaka is used to control the mosquito population in tropical climates.  The wild strain is a brownish-black.  Domesticated varieties are blue-black, red, and white.  Adult medakas tend to be 2 to 4 cm long.  They can be easily cultivated in very cold temperatures.  
	There a few differences between the male and female medaka.  The male’s anal fin is larger than the female’s.  The dorsal fin of the male also has deep notches.  The female’s dorsal fin is slightly smaller and a little more rounded.

Purpose

	To observe the development of the Japanese Medaka.

Materials

-stereoscope
-Medaka eggs

Procedure

	For the procedure, we counted the total number of eggs.  Then, we determined the number of living and the number of dead.  After, we determined the number of hatched living fish and the number of hatched dead fish.  We recorded the data.

Observations

Date	Live Eggs	Dead Eggs	Live Hatched	Dead Hatched	
Jan. 10	24	0	0	0	
Jan. 14	24	0	0	0	
Jan. 16	24	0	0	0	
Jan. 27	31	0	4	0	
Jan. 30	0	4	26	1	

Conclusions

1.	Totipotent is having unlimited capability to produce any type of cell.  Totipotent cells have the capability to turn into (to "specialize") into the tissues surrounding the developing embryo, the embryo, itself, and all of the tissues and organs that are present in the developed organism.
2.	Blastula is an early embryonic form produced by cleavage of a fertilized ovum and consisting of a spherical layer of cells surrounding a fluid-filled cavity. Also called blastosphere.
3.	The ectoderm is the outermost of the three primary germ layers of an embryo, from which the epidermis, nervous tissue, and, in vertebrates, sense organs develop. The mesoderm is the middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.  The endoderm is the innermost of the three primary germ layers of an animal embryo, developing into the gastrointestinal tract, the lungs, and associated structures. It is also called hypoblast.
4.	In birds and reptiles, the blood vessels in the yolk sac walls have a very important function in transporting nutrients to the embryo. The vessels hook up to veins that lead to the developing heart.  Then the contents are pumped throughout the body. In mammals, these vessels still form even though they don't have a vital supply function in the embryo (placenta replaces). Later on, they form gut blood vessels.  The amnion functions to provide a type of shock protection.  The chorion functions as a way to supply the embryo with nutrients.  It is also the embryo’s connection to the outside.  It is a little like the umbilical cord in mammals.  Lastly, the allantois stores the waste products of the embryo.  
5.	My hatch rate is definitely higher than the hatch rate in the wild.  This is because I did not have any natural predators for the fish.  Most likely, in the wild, many of the fish would have been eaten or crushed.  In our lab, there was nothing there to prevent the fish from hatching. 
6.	In protostomes, the blastopore in the mouth instead of the anus.  Also, it undergoes spinal cleavage, which is when the embryo changes from four cells to eight cells. The cells divide at slight angles to one another, so that none of the four cells in one plane of the eight-cell stage is directly over a cell in the other plane.  They also undergo determinate cleavage, which is when the daughter cells develop into specific tissues.  This is determined after cell division.  Finally, protostomes have schizocoelous development of the coelom.  This is when the coelom and the mesoderm develop from a mass of mesoderm tissue, and then it splits down the middle.   Examples of protostomes are mollusks, annelids, and arthropods.  In deuterosomes, the blastopore develops in the anus instead of the mouth.  They also undergo radial and indeterminate cleavage.  Radial cleavage is when the embryo changes from four to eight cells, and the cell planes are directly on top of each other.  Indeterminate cleavage is the cells do not develop into specific tissues, but go on to develop into the entire organism.  Lastly, there is enterocoelous development of the coelom.  This is when the mesoderm and coelom develop as small sacs on the digestive tract.  Some examples of deuterosomes are animals from echinodermata and chordate.

References

http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/Medaka_videos.html

http://home.earthlink.net/~zaptos/website/vocab/totipotent.html

http://www.brynmawr.edu/biology/db/lect6.1+6.2.html

http://www.utm.edu/~rirwin/protodeutero.htm