Increased ability to compete for food by growth hormone-transgenic coho salmon Oncorhynchus kisutch (Walbaum) R H Devlin 1 , J I Johnsson 2 , D E Smailus 1 , C A Biagi 1 , E Jo È nsson 2 & B Th Bjo È rnsson 2 1 Fisheries and Oceans Canada, 4160 Marine Drive, West Vancouver, British Columbia V7V 1N6, Canada 2 Department of Zoology, Go Èteborg University, Box 463, SE-405 30 Go Èteborg, Sweden Correspondence: J I Johnsson, Department of Zoology, Go Èteborg University, Box 463, SE-405 30 Go Èteborg, Sweden Abstract In salmonids, growth hormone (GH) stimulates growth, appetite and the ability to compete for food. This study tested the hypothesis that increased GH levels in GH-transgenic coho salmon Oncorhynchus kisutch (Walbaum) increase competi- tive ability through higher feeding motivation. The transgenic strain of salmon used contained a gene construct consisting of the sockeye metallothionein- B promoter fused to the type 1 growth gene coding region. The transgenic animals (mean size = 250 g) were F 1 individuals. In six consecutive feeding trials, the intake of contested food pellets by size-matched pairs consisting of one control (1 year older non- transgenic coho salmon) and one GH-transgenic coho salmon was compared. Pellets were provided sequentially until neither ®sh took three consecutive pellets; the identity of the ®sh taking each pellet was noted. Calculated on the three ®rst pellets offered at each feeding trial, the transgenic coho salmon consumed 2.5 times more contested pellets than the controls, supporting the hypothesis that GH transgenesis increases the ability to compete for food. Overall, the transgenic ®sh consumed 2.9 times more pellets that the non-transgenic controls, indicating a high feeding motivation of the trans- genic ®sh throughout the feeding trials. It appears that GH transgenesis and GH treatments can induce similar changes in the feeding behaviour of salmo- nids. Depending on how transgenic and wild individuals differ in other ®tness-related characters, escaped GH transgenic ®sh may compete success- fully with native ®sh in the wild. Introduction Growth hormone (GH) stimulates tissue growth by increasing the rate of cell proliferation and differ- entiation (Isaksson, Ede Ân & Jansson 1985). In ®sh, the growth-promoting effects of GH are well documented (McLean & Donaldson 1993; Bjo Èrnsson 1997). The use of GH has been legalized recently for dairy production in the USA (Gershon 1994), and the potential uses of GH are currently being explored in aquaculture, including the altera- tion of GH gene expression in ®sh by transgenesis. Such research has created salmon that can average up to 11-fold heavier than normal ®sh after 1 year of growth (Devlin, Yesaki, Biagi & Donaldson 1994). The use of transgenic animals is frequently debated and, for salmon, major concerns are the high escape rates from production facilities and potential inter- actions between farmed and wild ®sh (Gausen & Moen 1991; Devlin & Donaldson 1992). This concern is further emphasized by recent work showing that GH injections alter several behaviour components in ®sh, including an increased ability to compete for food (Johnsson & Bjo Èrnsson 1994; Johnsson, Petersson, Jo Ènsson, Bjo Èrnsson & Ja Èrvi 1996; Jo Ènsson, Johnsson & Bjo Èrnsson 1996). This supports the hypothesis that GH treatment increases metabolic demands and feeding motivation, which in turn increases appetite and competitive ability. However, it is not known whether the behaviour of GH transgenic ®sh is altered in a similar way. Thus, the relative competitive ability of transgenic ®sh and wild conspeci®cs is not known, which makes it dif®cult to evaluate the potential impact of escaped R # 1999 Blackwell Science Ltd 479 Aquaculture Research, 1999, 30, 479±482