Medaka egg hatching time is influenced primarily by water temperature and is typically calculated using a cumulative temperature method. A commonly accepted guideline is a total of 450°F. To estimate when eggs will hatch, multiply the daily water temperature (in °F) by the number of days. For example, at 77°F, hatching usually occurs in about 5.8 days—so you can expect fry to emerge in roughly 6 days.

This principle is part of what’s known as a temperature coefficient model, which explains how biological processes accelerate with temperature increases.

Once medaka fry hatch, they are extremely small and vulnerable. If left in the same container with adult medaka, they may be eaten—even by their parents. That’s why it’s essential to separate fry into their own tank or container as soon as they hatch to ensure their survival.

Newly hatched fry rely on their yolk sac for the first 2–3 days, after which they’ll need external food. To support healthy growth, provide finely crushed food multiple times a day. We recommend using our Itosui Medaka Food, a specialized formula designed specifically for baby medaka fry.

Understanding medaka egg hatching time is essential for any breeder looking to raise healthy fry. By monitoring the temperature closely and following proven incubation techniques, you’ll increase the survival rate and improve the overall success of your medaka breeding efforts.

In addition to temperature, factors like water quality, oxygen levels, and light exposure can also influence medaka egg hatching time. Keeping the environment clean and stable plays a critical role in ensuring healthy development. Avoid overcrowding and perform partial water changes if necessary to prevent the build-up of harmful substances.