We describe the production of transgenic rainbow trout (Oncorhynchus mykiss) and tilapia (Oreochromis niloticus) by microneedle injection of fertilized eggs with cloned copies of novel gene constructs. Two aspects of the work with transgenic trout are presented; namely, patterns of inheritance of transgenes by the F1 generation following in vitro fertilization of gametes from transgenic and nontransgenic fish, and the degree of DNA methylation of transgenes in different fish and in different tissues of the same fish. Work with transgenic tilapia has been only of short duration, and evidence is presented simply to indicate their transgenic status. Transient expression studies using the bacterial gene chloramphenicol acetyltransferase when driven by fish-derived promoters are also discussed.