The Killifish Life Cycle

Killifish, or pupfish, are quite possibly the most remarkable group of vertebrates living today, comprising around 100 species of small fish grouped into the family Cyprinodontidae. They have a wide distribution range, encompassing the Americas, Africa, Europe, and Asia. Among these is the only vertebrate species known to be capable of self fertilization, the mangrove killifish (Kryptolebias marmoratus). Male killifish can be dazzlingly colorful, but the family is most famous for the ability of some of its species — the annual killifish — to survive as eggs through prolonged droughts.

What habitats do annual killifish live in?

In arid regions, brief rainy seasons give rise to temporary pools of various sizes, ranging from broad, shallow oases to tiny puddles created by an elephant's footprint.These exist for perhaps a few weeks, dwindling under the hot sun until they disappear. Incredibly, the killifish have succeeded in adapting to
this habitat, where they briefly flourish, growing to maturity, spawning and dying within weeks.

How do the killifish eggs survive drying out?

The killifishe's secret is in their superbly adapted eggs. The shell is layered to protect the developing embryo, specifically to prevent it from drying out When the rain arrives it acts as a trigger, causing the embryo inside to begin to grow. Until this happens the embryo remains in a state of suspended animation, properly known as diapause, for months or even years.The fish also have a mechanism to prevent a brief shower from activating the eggs at the wrong time and causing the local population to die out; a proportion of the eggs in each batch will not hatch until soaked and dried a second time. It is not just the presence of water that promotes hatching either A drop in the level of dissolved oxygen and an increase in carbon dioxide in the water are thought to instigate the final stage of hatching. These patterns of dissolved gases in the water are some indication of the presence of infusorians, which provide the larva's first meal.

What is the life cycle of these killifish?

When the rains arrive, those embryos that succumb to temptation and hatch are immediately engaged in one of the most accelerated life cycles of all vertebrate animals.The race is now on to complete their life cycle before the pool dries up. Unlike most fish, killifish larvae are not provisioned with yolk sacs and therefore need to hunt for food as soon as they hatch. From this moment forward they feed voraciously and, if conditions allow, grow extremely rapidly; fish of the genus Nothobronchius are reputed to reach maturity after as little as 30 days. Males, in particular, are aggressive as they have much at stake — one breeding season to get it right and plenty of competition to contend with.This urgency is also reflected in the brilliant colors typical of the male annual killifish, each contender hoping to attract as many females as possible to mate. If and when he is successful, the pair swim side by side, delivering fertilized eggs into the muddy bottom of their home. Although annual killifish can live for over a year in the aquarium, their wild counterparts seldom survive long after spawning — having laid their eggs, their mission is complete and their life is curtailed by the seasonal drying of the pool once more.

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