AEI 3:231-243 (2013)  -  DOI: https://doi.org/10.3354/aei00065

Ecological interactions between hatchery and wild fish: a case study based on the highly piscivorous Japanese Spanish mackerel

Kaori Nakajima1, Shuichi Kitada1,*, Hideki Yamazaki2, Hiromasa Takemori3, Yasuhiro Obata4, Akio Iwamoto5, Katsuyuki Hamasaki1

1Dept. Marine Biosciences, Tokyo University of Marine Science and Technology, Tokyo 108-8477, Japan
2Momoshima Laboratory, National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency (FRA), Hiroshima 722-0061, Japan
3Kagawa Prefectural Fisheries Experimental Station, Takamatsu 761-0111, Japan
4National Research Institute of Fisheries and Environment of Inland Sea, FRA, Hiroshima 739-0452, Japan
5National Research Institute of Aquaculture, FRA, Mie 516-0193, Japan
*Corresponding author. Email:

ABSTRACT: If the release of hatchery-reared juveniles exceeds the carrying capacity of the environment, the growth rate of wild fish may decrease or hatchery fish might displace wild fish because of competition for prey and space, or cannibalism. However, limited evidence is available to confirm these ecological effects. Therefore, we used census-marking experiments to investigate the ecological interactions between hatchery and wild fish in the large piscivorous species Japanese Spanish mackerel (JSM) Scomberomorus niphonius in the Seto Inland Sea. We analysed the relationship between the mean body weight and population size of Age 0 JSM, and the relationship between the biomass of juvenile Japanese anchovy Engraulis japonicus, which is the principal prey fish of JSM, and that of Age 0 JSM. We also estimated the spawner–recruit relationship. We measured the body sizes of 5008 JSM juveniles during July and December between 1999 and 2005 in the eastern Seto Inland Sea, and 551 hatchery fish were identified in the sample based on examinations of marked otoliths. There was a negative correlation between the mean body weight and population size of Age 0 fish, which clearly demonstrated the density-dependent growth of Age 0 JSM. The ~35% variation in the biomass of Age 0 JSM was explained by the biomass of prey fish. Hatchery fish tended to be larger than wild fish, and they had better growth performance. Our analysis showed that hatchery fish reduced the growth rate of wild fish and displaced the wild fish in terms of biomass when hatchery fish stocking exceeded the carrying capacity of the environment.


KEY WORDS: Displacement of wild fish · Carrying capacity · Density-dependent growth · Prey fish dynamics · Otolith marking · Scomberomorus niphonius · Marine stock enhancement


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Cite this article as: Nakajima K, Kitada S, Yamazaki H, Takemori H, Obata Y, Iwamoto A, Hamasaki K (2013) Ecological interactions between hatchery and wild fish: a case study based on the highly piscivorous Japanese Spanish mackerel. Aquacult Environ Interact 3:231-243. https://doi.org/10.3354/aei00065

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