Journal of Fish Biology (2009) 75, 1459–1472 doi:10.1111/j.1095-8649.2009.02393.x, available online at www.interscience.wiley.com Elevated ability to compete for limited food resources by ‘all-fish’ growth hormone transgenic common carp Cyprinus carpio M. Duan*†, T. Zhang*‡, W. Hu*, L. F. Sundstr¨ om§, Y. Wang*, Z. Li *‡ and Z. Zhu* *State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China, †Graduate University of Chinese Academy of Sciences, Beijing 100049, China and §Department of Fisheries and Oceans, University of British Columbia, Centre for Aquaculture and Environmental Research, 4160 Marine Drive, West Vancouver, British Colombia V7V 1N6, Canada (Received 6 December 2008, Accepted 2 July 2009) Food consumption, number of movements and feeding hierarchy of juvenile transgenic common carp Cyprinus carpio and their size-matched non-transgenic conspecifics were measured under conditions of limited food supply. Transgenic fish exhibited 73·3% more movements as well as a higher feeding order, and consumed 1·86 times as many food pellets as their non-transgenic counterparts. After the 10 day experiment, transgenic C. carpio had still not realized their higher growth potential, which may be partly explained by the higher frequency of movements of transgenics and the ‘sneaky’ feeding strategy used by the non-transgenics. The results indicate that these transgenic fish possess an elevated ability to compete for limited food resources, which could be advantageous after an escape into the wild. It may be that other factors in the natural environment (i.e. predation risk and food distribution), however, would offset this advantage. Thus, these results need to be assessed with caution. © 2009 The Authors Journal compilation © 2009 The Fisheries Society of the British Isles Key words: competition; foraging; growth hormone (GH); transgene. INTRODUCTION The use of growth hormone (GH) treatment (McLean & Donaldson, 1993) and altered GH gene expression in fishes by transgenesis (Zhu et al ., 1985; Gross et al ., 1992; Devlin et al ., 1994) have been explored as a way to increase aquaculture production and efficiency. Fast-growing fishes also have been considered as the best candidates for the marketing of transgenic animals for human consumption (Zbikowska, 2003). Released or escaped fast-growing transgenic fishes, however, pose an ecological risk that should be of concern (Devlin et al ., 2006). Assessment of the environmental effects of fast-growing transgenic fishes is therefore urgently needed (Kapuscinski et al ., 2007). ‡Authors to whom correspondence should be addressed. Tel.: +86 27 6878 0369; fax: +86 27 6878 0063; email: tlzhang@ihb.ac.cn; zhongjie@ihb.ac.cn 1459 © 2009 The Authors Journal compilation © 2009 The Fisheries Society of the British Isles