Post-Release Performance and Assessment of Cage-Conditioned Japanese Flounder, Paralichthys olivaceus, in Wakasa Bay, Japan

Abstract

Conditioning is the process of providing individuals reared for stock enhancement with some degree of “natural” experience prior to release. Conditioning flatfish in predator-free cages may help adjustment to the wild. From 2008–2010, the Obama Laboratory conducted pre-release, experimental cage conditioning for Japanese flounder in both the Takahama and Obama portions of Wakasa Bay, Japan. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen. The objectives were to describe how characteristics of released flounder changed with cage exposure and to determine how recapture rates compared between conditioned and non-conditioned fish. Significantly more conditioned fish were recaptured than non-conditioned fish in Obama Bay in 2010 (p < 0.05). In 2008 and 2009, recapture rates of conditioned and non-conditioned flounder followed the same trend, although these were not significantly different. Laboratory experiments revealed that conditioned fish had significantly better burying abilities (p < 0.001) and enhanced feeding abilities compared to non-conditioned fish. This study is the first to examine flatfish conditioning strategies using market data and shows that cage conditioning can favorably alter the attributes and recapture rates of released fish.