The present invention features compositions and methods for effectively altering PUFA content in animal cells, i.e., cells other than C. elegans, such as cells of birds or fish, such as muscle cells, nerve cells ( in the peripheral or central nervous system), adipocytes, endothelial cells, and cancer cells, the composition includes a nucleic acid encoding fat-1, which is optionally and operably linked to a persistently active or tissue-specific promoter or Other regulatory sequences, and pharmaceutically acceptable formulations with nucleic acids or biologically active variants thereof. The compositions and methods include a modified fat-1 gene, wherein the gene contains at least one optimized codon. The modified cells, whether in vivo or in vitro (i.e., in tissue culture), transgenic animals (especially fish and birds) comprising these modified cells, and food obtained from those animals (also That is, meat or other edible parts of animals (ie, liver, kidney or pancreas) are also included within the scope of the present invention.