Experimental design of spawning experiments.

Fish groups are wild-type (NT) or growth hormone transgenic (T) coho salmon reared from smolt in a 350,000 L seawater Mesocosm, in Nature, or in standard Culture (4000 L tank). I. No Competition experiments consisted of single male×female pairs in spawning channels for 48 h. II. Full Competition experiments consisted of mixed male and female fish of two fish groups, 4 fish per fish group and sex, for a total of 16 fish in each spawning arena. III. High Male Competition experiments consisted of 4 male fish each of two different fish groups, competing for 4 NT Nature females, for a total of 12 fish in each spawning arena. For experiments I. and III. transgenic fish were ration restricted as juveniles (age at maturity = 3 years), and all NT fish were reared as juveniles at CAER. For experiment II. transgenic fish were fully fed as juveniles (age at maturity = 2 years), and NT fish were a mix of fish reared as juvenile at CAER, and those reared as juveniles at the Chehalis Enhancement Facility. Age of NT fish at maturity was 3 years (Mesocosm and Nature-reared) or 3–4 years (Culture-reared).1Experimental unit for I = one spawning pair, experimental units for II and III = one arena.2Due to limited fish numbers, this arena consisted of 3 fish per genotype and sex for a total of 12 fish.