how's is the recombinant dna of genetic modified atlantic salmon made ? What is the restriction enzyme to obtain the dna from other fishes ?

the methods from the paper below state

The experimental transgenic fish as well as the non-genetically modified control fish were Atlantic salmon (Salmo salar) bred from partially domesticated Saint John River stock, New Brunswick, Canada and reared at AquaBounty Farms in Prince Edward Island, a government-inspected hatchery designed with the required containment measures to prevent the escape of genetically modified organisms into the natural environment.

In the fall of 1989, the GH transgene was micro injected (approximately 106 copies per egg) through the micropyle into the cytoplasm of fertilized, non-water activated salmon eggs(Shears et al., 1992). This transgene was composed of a chinook salmon GH gene attached to an antifreeze protein promoter sequence taken from the ocean pout (Hew et al., 1995). Milt from one of the fast-growing transgenic males arising from the injected eggs (P1— Parental generation), which sexually matured in the fall of 1991, was crossed with a non-transgenic female. A fast-growing, transgenic female (F1) resulting from this mating was crossed with a non-transgenic male in the fall of 1996 resulting in the F2 transgenic fish used in the present study. Also, in the fall of 1996, pooled non-transgenic milt and eggs from the same Saint John River stock were used to generate non-transgenic control fish.

Transgenic and control families of embryos and alevins were incubated in separate trays in flow-through, stacked-tray incubator. To facilitate having transgenic and control fish of approximately the same weight at the start of the experiment, the batch of eggs giving rise to the transgenic fish was incubated at a lower water temperature (4°C) relative to control eggs (7°C). Consequently, time at first feeding was approximately 17 days greater for the transgenic fry than for control fry.

In 1996, the progeny resulting from the cross between a transgenic female (F1) and a non-transgenic male exhibited a bimodal size distribution at the fingerling stage in June, a phenomenon not usually seen until the first autumn of growth Thorpe, 1977 and Thorpe et al., 1980. Consequently, the two modes could be separated into two groups based on fork length above and below 8.0 cm, with 50% of total population in each mode, which is typical of Mendelian segregation of an allelic insert on a single chromosome. This separation was later confirmed by the exclusive presence of the transgene in the upper modal group as revealed using polymerase chain reaction. The transgenic fish used in the present experiment were from the upper modal group of fish from the 1996 spawning. … 8600003318