The nation’s top koi aficionados will bring their most spectacular fish — up to 3 feet long — to South San Jose to compete this weekend in the ZNA NorCal National Koi Show.

The public’s invited to come and gaze at 25 tanks’ worth of koi contestants, learn about the hobby of keeping koi and see the judges in action. Admission is free.

The ZNA (Zen Nippon Arankai) outdoor show has been held in San Jose for a number of years, with fish competing in several koi classifications for color and scalation patterns.

Organizer Dinh Nguyen said the primary purpose is to advance koi education, from how to begin in the hobby to offering the latest information about koi keeping — with an emphasis on appreciation for the “living art” of koi, or nishikigoi in Japanese.

Besides the koi competition and related exhibits, the weekend event will feature Tuan Vo, a calligraphy master, and members of the California Calligraphy Association doing calligraphy to raise funds for ZNA NorCal scholarships for students around the world. Bonsai demonstrations are also planned.