A new step-by-step procedure makes it easier to separate fish by gender
for growth performance, physiological studies and to manage broodstocks for
reproduction and genetic selection.
The systematic method to segregate yellow perch females from males
during early growth stages has been developed by physiologist Brian Shepherd and
his colleagues at the Agricultural Research Service (ARS) Dairy Forage and
Aquaculture Research Unit in Milwaukee, Wisconsin. 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% 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.