Killifish

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Killifish

by Harry F. Sanders, III on January 31, 2019

Killifish are common in the pet trade and come in varying sizes and colors. They have increasingly become common as lab animals as well. Researchers use them to study aging in humans since they mature quickly. But did you know they are also strong evidence for God’s original design for the world?

Killifish are unique fish with a lot of different colors and shapes. There are over twelve hundred species. They are popular aquarium fish as well. Killifish lay eggs which hatch into tiny fish called fry. Some species are annual, meaning they live a year or less; others can live for several years. Despite the fearsome name, killifish are not dangerous and are usually very small.

Scientists use some killifish to study how people age because they grow up very quickly. They become adults in as little as two weeks! This is very important because these are annual killifish. They need to grow up quickly so they can lay eggs before their homes evaporate and they die. Their homes are puddles in African savanna and South American rainforest. These puddles only exist during the rainy season. Sometimes they dry up within three weeks of being filled. When they dry up, the fish die. But before they die, they lay their eggs in the mud.

The eggs of these killifish need a special design to survive without water for up to ten months. Since there is no water, the eggs lose water to evaporation. They also do not get oxygen. But God has designed the eggs to be able to use up to 90% less oxygen than a normal fish egg and thrive. He has also built in a special sugar called trehalose. The fish use trehalose to replace water until they hatch.

The eggs have to wait for water to hatch, or the fry will die. To do this, they go into something similar to hibernation called diapause. Diapause slows down the fries’ (not the French version) development so that they don’t hatch too soon. Eggs can wait a very long time. Some eggs have hatched after three years in diapause! Once the eggs get just the right signals from temperature, light, and water, they will hatch and start the cycle over again.

These annual killifish are specially designed to live in these tiny puddles. Most likely their ancestors got trapped in some of these puddles as the water flowed back into the oceans after the flood. Because they already had the ability to breed quickly and survive up to three years without water, these killifish were well suited to the environment they found themselves in. Since most other fish were not suited to it, when the puddles dried up, other fish in the puddle died. The killifish eggs in the mud, however, survived and hatched when the next rainy season came. What a wonderful God we serve, who took care to design even a tiny fish to survive in a difficult situation. How much more does he care for us, who are made in his image?