*2.2.14 Transgenesis*

Transgenics are those genetically engineered organisms which have heterologous DNA (transgene) integrated stably into their genome through artificial means like microinjection, electroporation, sperm mediated transfer, lipofection, retrovirus, etc. The transgene construct carries a target gene, encoding product of interest and regulatory elements that regulate the expression of the gene in a spatial, temporal and developmental manner [44]. Since the development of the first transgenic fish in 1984, a wide number of transgenic fish species have been produced (**Table 2**) to improve growth, disease resistance, cold resistance, etc. [45].
