Much to the amazement of the researchers at UK's Hull University, they were startled to find that a hybrid female fish had developed testicles, self-fertilized her eggs and even given birth to offsprings.

The hybridized fish was that of the cichlid species, tropical freshwater fish also referred to as "hopeful monsters." It was aquarium-bred under laboratory settings at the university where it ended up growing both the male and female sex organs.

Insects and flowers alike naturally breed via the process of self-fertilization, which is also referred to as "selfing." In the case of animals, birds, fish and other vertebrates, both male and female species are usually required for fertilization and the subsequent reproduction of their young to take place.

Selfing has been previously observed in another species of fish namely the mangrove killifish. In this species' case, self-fertilization is their natural and basic way of reproduction.

Ola Svensson, lead author and researcher from the University of Gothenburg's Department of Biological and Environmental Sciences, told Discovery News that in the case of mangrove killifish, selfing is an adaptation since it can be hard for them to find a mate. Selfing in such instances is better than not producing at all.

The researchers at Hull University had come across two varied species of cichlids that eventually resulted in reproducing this hybrid self-fertilizing fish. According to them, hybridizations of such nature do occur in the wild as well as in laboratories.

Over the course of one year, this strange fish had given birth to 46 offsprings.

"In total, this intersex produced 14 broods, raising 46 living F2-juveniles over a period of 25 months while in isolation in a 20 × 20 × 20 aquarium. Two sons and 15 daughters survived to adulthood and were fertile," the study mentions.

To further study this strange phenomenon, the researchers confined 18 sibling sisters and 12 daughters into isolation for a period of one year. This was to determine if these female fish would by any chance to self-fertilize in a similar manner like their sisters and mother, but it did not occur.

However, when the same set of female fish was crossed with their male counterparts, they reproduced offsprings.

The remarkable findings were published in the journal Royal Society Open Science, on Wednesday, March 23.

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