This paper examines the price formation of John dory Zeus faber Linnaeus on the ex-vessel market. We use daily data across 13 ports during the period April 20 August 31, 2014 in Mie Prefecture, Japan. Since the supply at these landing markets can be reasonably considered to be perfectly price-inelastic, the observed price and quantity are expected to follow a downward sloping demand curve. The observed relationship, however, turns out to be upward sloping for the most part. This relationship remains in our regression analysis after controlling for the