Female Fish Grows Her Own Balls To Produce Offspring

A female fish has grown her own balls (male testis) to reproduce.

The cichlid fish that grew a pair to reproduce. OLA SVENSSON ET AL, ROYAL SOCIETY OPEN SCIENCE
The cichlid fish having both ovaries and testis. Photo credits: OLA SVENSSON ET AL, ROYAL SOCIETY OPEN SCIENCE

What do you do if you’re a female fish isolated in an aquarium and you need to further your generation? You grow a pair of balls and fertilise your own eggs, of course! The paper documenting this strange occurrence is published in the journal Royal Society Open Science.

At its death, the fish was found to possess ovaries as well as a male testis — it was intersex.

A female fish (a tropical freshwater cichlid) in an aquarium from Hull University based in the UK is said to have developed a male sex organ which she used to have her own eggs fertilised, resulting in 4 offspring, and 42 others in the following year; these were male or female, none of which were endowed with the sexual capability of their mother (or father).

This marks the first time a sexually-reproducing vertebrate has been discovered with the ability known as “selfing” — this refers to mating with oneself, and breeding as a consequence.

Among fish species that are known to do this is the mangrove killifish. For the latter, selfing is the main method of reproduction. The lead author of the new paper, Ola Svensson University of Gothenburg’s Department of Biological and Environmental Sciences, explains that selfing is an adaptation for the mangrove killifish; selfing is the better option for these fish as finding a mate is challenging, says Svensson in a statement to Discover News. But, this was not known for the cichlid fish.

Breeding occurred via the mouth. The fish is a mouth brooding one, says senior Cock van Oosterhout of the University of East Anglia, and fertilisation occurs in the mouth. Their eggs will be fertilised if spermatozoa are released at the same time, or this process might occur in the mouth of the fish.

This discovery is different from similar others because the fish in question was literally both the mother and the father of the offspring. According to Svensson, it remains a case of sexual reproduction.

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