Yellow perch. (Photo Credit: USDA)

New method distinguishes yellow perch sex

Identifying juvenile and adult yellow perch females from males is no longer an obstacle for aquaculture producers of this high-value fish, thanks to US Department of Agriculture (USDA) scientists. A new step-by-step procedure developed by the scientists makes it easier to separate fish by gender for growth performance, physiological studies and to manage broodstocks for reproduction and genetic selection.

Physiologist Brian Shepherd and his colleagues at the Agricultural Research Service (ARS) Dairy Forage and Aquaculture Research Unit in Milwaukee, Wisconsin, developed the systematic method to segregate yellow perch females from males during early growth stages. Because females tend to grow faster and larger than males, females could often be mistaken for males when being selected for genetic improvement prior to reproductive maturity. Previously, it was extremely difficult to identify gender until fish matured (up to two years).

The method involves an algorithm—a checklist that includes the size of the fish and the shape and colour of the anal and reproductive openings. The process is fast, easy, reliable and more than 97 per cent accurate in fish above three inches in length.

Factors such as size and geographical origin can affect external characteristics related to yellow perch gender. Therefore, scientists examined yellow perch strains from four different geographical areas, while considering body size and reproductive maturity. They then identified female and male characteristics that could be confirmed in yellow perch of various sizes from the four geographical strains.

The new system allows producers as well as scientists to identify the largest females and males for producing the next generation of yellow perch. Because fish are unharmed during the process, the method also can be used to identify females from males when wild yellow perch field surveys are taken.

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