LAUSR

Abstract Tiger pufferfish Takifugu rubripes (order Tetraodontiformes, family Tetraodontidae) is a highly exploited species and stocks continue to decline, although hatchery‐reared juveniles have been released since 1965 for stock enhancement. To determine why the stock has not recovered through hatchery‐release practices, this study investigated and compared the population characteristics of wild and hatchery‐origin fish. The length–mass relationship showed that hatchery‐origin fish were skinnier, with males weighing less than 90% of the mass of wild males of the same length. The hepatosomatic index tended to be lower in hatchery‐origin fish. Age was estimated using the otolith‐based method, and the estimates were more accurate and precise than those obtained by the conventional vertebra‐based method. At the age of 2.9 years, an age at which specimens were the most abundant in catches, hatchery‐origin males weighed only 67% of wild males. The maximum observed age was 12 years for wild fish and 5 years for hatchery‐origin fish. The instantaneous total mortality rates of hatchery‐origin fish were more than twice as high as those of wild fish. In summary, the hatchery‐origin fish had poor health status, poor growth and high mortality, and their fitness in natural environments was therefore hypothesized to be low throughout life.