Originally Posted by LittleBettaFish
So I think while they can live at colder temperatures (we get down to around 0-10 degrees Celsius in winter here) they prefer a temperature somewhere in the middle, which is what I always took temperate as meaning. Mine are being kept at 24 degrees Celsius as they are in with my honey blue-eyes who prefer a higher temperature.
I prefer to keep mine at as close as possible to their natural environment... With medaka, they are basically seasonal breeders. They breed based on the temperature and the daylight hours. As they don't stay in breeding shape all year in nature, their bodies cannot handle it. Keeping them in a heated tank may seem "happier" because they are always in breeding mode... But it seriously reduces the quality of the eggs and fry, and cuts their lifespan down to less than half. Medaka bred year round (kept at "optimal" temps) have short lifespans and tend to reach maturity at a smaller size and stay sort of stunted as they never have a good growing period without their bodies pushing toward reproduction.
Wild medaka live in streams, ponds, and pools that freeze over completely in the winter. As the pet versions are pretty much the same as the wild versions in everything but color, they do best in the same sort of environment.
As for artificially hatching, with killifish and my pseudomugil I pick the eggs out of the spawning mop daily as the adults will generally go through and eat them. Then I put them into a separate container (mine floats in my fry grow-out) add a couple drops of methylene blue to deter fungus and gently aerate with an airstone.
I would say yes then - you can artificially hatch the medaka eggs with no trouble. If you leave them attached to a plant, or remove the little strings that stick to plants and such, they hardly ever develop mold unless they are dead eggs to begin with.
Once the fry hatch in the container they are acclimatised over into the grow-out and raised as normal.
I have a nice little unit tank that attaches to the normal tank, doing a constant drip exchange of water. They can be moved pretty much immediately into the tank after hatching as it is the same water.
I love the Oryzias species. Just wish they were more readily available here.
I caught my wild ones myself.