One of the key concerns about a transgene escape is the "Trojan gene effect", caused when a GM fish outcompetes or reproduces equally against wild rivals, however if the resulting offspring are genetically inferior this could lead a species towards eventual extinction. Until now there is no empirical research to demonstrate the ability of transgenic Atlantic salmon to breed naturally and infiltrate the wild gene pool.

In the wild, reproducing males present two main forms of rivals which any escaping transgenic male would have to compete with; large males which have migrated and returned from the sea and smaller male parr which have matured in freshwater. The large males are aggressive and develop attributes to fight off their rivals, while the smaller male parr use cryptic coloring and 'sneak fertilization' to compete.

To measure the ability of transgenic males to complete with wild males during the reproductive season the team monitored breeding behavior in a naturalized laboratory setting and used genetic analysis to determine the success of competing individuals at producing offspring.