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. It is currently the only native Chinese fish species recommended by the national standard of China (GB/T29763-2013) in chemical testing methods and biological tests of wastewater detection, and many studies have used this species to evaluate the toxicological effects of both inorganic compounds and organic pollutants. 

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

The 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 and identified that the knocked-out of Protocadherin 10 (PCDH10L) affected the Pb²⁺ mortality of rare minnow.    

They 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 that in other autosomes, which indicates the sex chromosomes may have experienced rapid evolution.   

In addition, the 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, etc. This study provided detailed information of the rare minnow genome,” said Prof. CAO.