Fish clone themselves at Bristol aquarium

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Staff at Bristol Aquarium are celebrating the birth of five Mangrove killifish (Kryptolebias marmoratus), born despite not having a father.

The young fish are identical clones of their parent but are not the outcome of scientific experimentation or genetic manipulation by man, instead they are the result of a natural process known as parthenogenesis, where the fish is capable of self fertilisation.

There are no female Mangrove killifish, only males and hermaphrodites (fish that have both male and female sexual organs) and many populations are made up entirely of hermaphrodites, so are all clones giving birth to live young. Where the males do exist the hermaphrodites start behaving as females, laying unfertilised eggs which the males then fertilise externally.

Temperature plays a role in the numbers of males with temperatures above 25°C/77°F making all the fish hermaphrodite, while below 20°C/68°F most are males.

They were thought to be the only known naturally occurring, self fertilising vertebrate but recent research shows some lizard species such as the Komodo dragon and New Mexico whiptail are capable of the trick.

Other studies have shown that sharks are able to have 'virgin births', however the process differs as all young produced are female so the process would not be able to replace a depleted male population.

Mangrove killifish are also capable of surviving out of water for over two months as long as they stay damp. They are known to climb inside old insect burrows in trees and fallen logs during dry periods, and once there, change physiology so their gills retain water and nutrients and their skin excretes nitrogen. All these changes are reversed once the fish returns to water.

The Bristol Aquarium fish are part of a joint captive breeding programme with the Aberystwyth University.

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