Royal Society Open Science

A female fish has been observed undergoing a rare process in which it grew male reproductive organs and impregnated itself, going on to have offspring.

In a study published in the Royal Society Open Science journal, a team details the case of female cichlid hybrid fish, a freshwater fish often kept in aquariums. The team noticed that the fish were able to impregnate themselves, producing healthy offspring who behaved -- and reproduced -- totally normally.


The fish managed to impregnate itself by mixing sperm and eggs in its own mouth, ejaculating into the water and then sucking up the fluid into its mouth, where its eggs were.

The eggs were subsequently fertilised and developed into healthy offspring -- only one of which subsequently developed the same reproductive strategy.

The team note that the process is relatively rare -- although self-impregnation does occur elsewhere in the animal kingdom, it normally occurs because of lack of available mates. "Although such 'hopeful monsters' may be evolutionarily transient and rare in nature, certain environmental conditions may make them biologically significant," they write.

Other creatures also engage in 'selfing' -- many plants pollinate themselves, and animals including the New Mexico whiptail, a lizard, can impregnate themselves too.

Two cases of the phenomenon have also been recorded in komodo dragons, with females separated from males of the same species able to reproduce alone so she can subsequently mate with her male offspring.