(i) human or rat gene for growth hormone,

(ii) chicken gene for delta crystalline protein,

(iii) E. coli gene, for β-galactosidase,

(iv) E. coli gene for neomycin resistance,

(v) winter flounder gene for antifreeze protein (flounder = flat fish),

(vi) rainbow trout gene for growth hormone.

The technique of microinjection has been successfully used to generate transgenic fish in many species such as common carp, catfish, goldfish, loach, medaka, salmon, Tilapia, rainbow trout and zebrafish.

In other animals (e.g. mice, cows, pigs, sheep and rabbits), usually direct microinjection of cloned DNA into male pronuclei of fertilized eggs has proved very successful, but in most fish species studied so far, pronuclei can not be easily visualized (except in medaka), so that the DNA needs to be injected into the cytoplasm.

Since in fish, fertilization is external, in vitro culturing of embryos and their subsequent transfer into foster mothers (required in mammalian systems) is not required. Further, the injection into the cytoplasm is not as harmful as that into the nucleus, so that the survival rate in fish is much higher (35% to 80%).

Human growth hormone gene transferred to transgenic fish allowed growth that was twice the size of their corresponding non- transgenic fish (goldfish, rainbow trout, salmon). Similarly antifreeze protein (AFP) gene was transferred in several cases and its expression as studied in transgenic salmon. It was shown that the level of AFP gene expression is still too low to provide protection against freeze.