Set up for Viewing Medaka

Each team receives a few embryos in solution in a small Pitre dish so that they can look at the embryos under a microscope.  Medaka eggs are kept in a jar with rearing solution.  It is important to keep the lid slightly open or completely open to let oxygen enter the jar.  Transfer an embryo to a concave slide with a transfer pipette or look at the embryos while in the Petri dish under the microscope.  Be sure there is some solution with the embryo, but not so much as to overflow the plate or well in the slide.  The eggs are relatively large, so the lower power of the microscope – a 4X or 5X objective lens – should be all that is needed to view the embryos. However, you may want to look under higher power.  It is important to gently move the embryo with the pipette or some blunt object so you can have the embryo in a position that allows you to see the cells and that the yolk is not in the way of viewing the cells. You may also have to adjust the amount of light with the diaphragm or light aperture control.  Look for the heart and pigmented eyes as the embryo matures. Remember that you might have to gently move the embryo with the edge of a pipet to get it into a good viewing position.  Determine the stage of the eggs by comparing what you see by looking at the embryo to the diagrams. Make a simple diagram of the embryo.  Record your observations on the Live Medaka Embryo Observation Table [Live Medaka Record Table Web page or downloadable MS Word Document]. Take a picture of the embryos if possible. Repeat every 2 days until the embryo hatch. When the fish hatch transfer them to a tank of dechlorinated water without an aerator.  When they grow to about 1/4 inch long  begin to feed them small amounts of fry food and aerate them with an air pump and air stone.

Medaka breed in a photocycle of 14 hours of light and 10 hours of dark.  When the light comes on after being dark the eggs are layed and they need to be harvested.  When you see the eggs remove the female fish from the tank and gently remove the eggs from her.  Put the female fish immediately bak in the tank and put the eggs in a pitre dish with rearing solution.

Attachment #8

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