Rare minnow (Gobiocypris rarus) is a freshwater cyprinid species with a relatively small size, transparent eggs, large eggs, frequent spawning, high fecundity, and short generation span. In current chemical testing methods and biological tests of wastewater detection, only this native fish species is recommended by the Chinese national standard (GB/T29763-2013).     

In a collaboration with Dr. REN Yandong from Northwestern Polytechnical University, the research team led by Prof. CAO Hong from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences performed the genome sequencing, assembly, and annotation for rare minnow, and revealed that the mechanism underlying the rare minnow’s high sensitivity to environmental pollution, chemicals, and grass carp reovirus (GCRV) and identify the sex determination mechanism in rare minnow. The study was published in Science Advances.      

In this study, researchers investigated several specific mutation genes and specific lost genes of rare minnow, which might be related to the sensitivity of rare minnow to environmental stimuli. By doing this, they identified that the knocked-out of Protocadherin 10 (PCDH10L) affected the Pb²⁺ mortality of rare minnow.    

The researchers then identified the Z chromosome and partial W chromosome in this rare minnow genome, proving that the sex determination mechanism of rare minnow is ZZ/ZW. The TE content in sex chromosomes and the gene Ka/Ks value in sex chromosome are much higher than in other autosomes, which indicates the sex chromosomes may have experienced rapid evolution.   

In addition, researchers investigated the mechanisms of the differences of the hemorrhagic symptoms in the GCRV infected rare minnow and zebrafish (Danio rerio). Through the analysis of the gene expression level in different organs/tissues, they found that several IFIT genes may play key roles in GCRV resistance.   

“Scientists in China have been using rare minnows for years as experimental animals to study molecular toxicology, immunology, and biological and evolutionary research. Based on this study and the detailed information of the rare minnow genome it provided, scientists will be able to use gene-editing technology to conduct research in the future,” said Prof. Cao.