The initial thrust into genetic engineering of fish focused primarily on growth hormone transgenesis. The vast majority of experiments resulted in faster growing fish ranging from 10% to an amazing 30X increase in growth rate, typically a doubling. If triploidy was used to sterilize these fish, about half of the growth enhancement was lost, although unpublished commercial data indicated that this could be corrected with family selection. Different transgenic families had a wide range of performance; thus this technology always needs to be coupled with selection to maximize performance regardless of the transgene. Growth hormone gene transgenesis results in many pleiotropic effects including increased feed consumption and feed conversion efficiency, variable changes in disease resistance, changes in body composition, primarily increased protein percentage and decreased fat percentage coupled with changes in muscle ultrastructure. Additionally, behavioral changes can occur and most fitness traits are adversely but variably affected such as reproduction, foraging ability, predator avoidance and swimming ability.
Antimicrobial peptide transgene genetic engineering has consistently increased disease resistance of transgenic fish. Transfer of omega-3 fatty acid biosynthesis genes increased omega-3 fatty acid levels and the omega-3/omega-fatty acid ratio. Negative and positive pleiotropic effects have resulted from the transfer of omega-3 fatty acid transgenes. Random transfer of shrimp DNA affected flavor and nutritional values. Creation of Glo-fish having florescent jelly fish genes has resulted in a variety of new ornamental phenotypes and was the first commercialization of transgenic fish. Use of such florescent reporter genes in experiments should be questioned as the performance of these transgenic fish is damaged. Strain, family, genetic background and insertion site are among factors that affect transgenic performance.
Although environmental risk data indicated transgenic fish would likely be selected against in the natural environment, society requires strict confinement of transgenic fish. Transgenic sterilization or gene editing coupled with hormone therapy are the best options to ensure no long-term ecological effects of transgenic fish. Gene knockin/knockout has arrived. By targeting growth regulating and reproductive loci, reversibly sterile transgenic fish can be created that have increased growth, disease resistance and omega-3 fatty acid levels among others in a single fish. The best aquaculture genotypes today and in the future will be developed by using multiple genetic enhancement programs simultaneously or in sequence.
Public education is a major impediment to the acceptance of transgenic fish as food. There is no logical food safety issues with transgenic meat except for allergenicity in specific cases. The basics will always be important as the phenotype is a result of the genotype, environment, genotype-environment interaction and epigenetics. These principles are related to the commercialization of the first commercially approved transgenic fish, growth hormone gene transgenic Atlantic salmon, on the brink of failure. The best genotype in the world cannot perform well without the proper environmental input and application.