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The bottarga roe gene: sex-determining gene found in the flathead grey mullet

08.01.2021

Markers linked to the FSHR gene (Follicle Stimulating Hormone Receptor) of the flathead grey mullet (Mugil cephalus) allows fisheries to know, with high probability, whether the fish is male or female during the earliest stages of development. The discovery was made thanks to the sequencing of the mullet genome; the discovery was conducted by a research team from the University of Padua in collaboration with the University of Cagliari, ISPRA and the Greek "Fisheries Research Institute".

The results of the study published in the iScience journal entitled ‘Fshr, a fish sex-determining locus shows variable incomplete penetrance across flathead grey mullet populations’ helps to understand the complex system of sex determination in fish holding genetic, environmental, and ‘social’ components. In fact, there are species of fish that change sex at a certain age, including the sea bream (l’orata) which are male first then become female after two years of maturation. Some fish species change sex based on environmental factors, such as temperature, or due to an unbalanced population ratio where there are too many females or too many males. In the case of the flathead grey mullet, it seems that the sex is decided early on and that the FSHR gene plays a decisive role in such a “decision’.

Prof. Tomaso Patarnello from the Department of Comparative Biomedicine and Nutrition at the University of Padua and coordinator of the research together with Luca Bargelloni explains, "Not only does this information holds great scientific value, considering the poorly understood complex system of sex determination in fish, but it also holds great applicative importance. The commercially desired bottarga roe (a highly-priced food delicacy) is produced in the female gonads of mullets and until sexual maturity, at 2-3 years old, it is not possible to establish the sex apart from conducting a histological examination of the gonad.”

Selecting females before sexual maturity, in the natural environment, could reduce (potentially in half) the effort and costs of producing bottarga roe. "This translates into a marked increase in the production of bottarga roe with an increase in income for local operators and reducing egg roe imports from abroad," says Angelo Cau, professor at the University of Cagliari, promoter of this study.