Female fish grows testicles and fertilizes itself in strange case of ‘selfing’

MARCH 23, 2016

by Brett Smith

Desperate times call for desperate measures, and for a female tropical fish known as a cichlid, that means growing a testicle when there aren’t any males to mate with.

According to a report published in the Royal Society Open Science journal, the gender-additive fish, or ‘hopeful monster’, was ultimately able to fertilize its own eggs and produce fertile offspring.

"Selfing" when no mates are available

The phenomenon is the first known example of "selfing" in a vertebrate that normally reproduces sexually, the study authors said. Self-fertilization has been observed in mangrove killifish, but selfing is the primary mode of reproduction for those fish.

"In the mangrove killifish, selfing is an adaptation," lead author Ola Svensson told Discovery News. "It is believed that it can be hard for them to find a mate, and selfing is better than not producing at all."

The study began with the examination of Crenicara punctulata and Cichlasoma portalegrense, two species of cichlid believed to have the ability to change sex. In the course of that research, scientists produced a hybrid offspring not seen in nature. The hybrid fish then shocked researchers by producing four offspring. Then, over the ensuing year, she produced 42 more.

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