Fatty acid desaturase with bifunctional delta-5 and delta-6 activities. Component of a lipid metabolic pathway that catalyzes the biosynthesis of polyunsaturated fatty acids (PUFA) with preference toward n-3 substrates and Delta-6 function. (9Z,12Z)-octadecadienoyl-CoA + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = (6Z,9Z,12Z)-octadecatrienoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O (9Z,12Z,15Z)-octadecatrienoyl-CoA + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = (6Z,9Z,12Z,15Z)-octadecatetraenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O (8Z,11Z,14Z,17Z)-eicosatetraenoyl-CoA + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O (8Z,11Z,14Z)-eicosatrienoyl-CoA + 2 Fe(II)-[cytochrome b5] + 2 H(+) + O2 = (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + 2 Fe(III)-[cytochrome b5] + 2 H2O Lipid metabolism; polyunsaturated fatty acid biosynthesis. The protein sequence includes a number of characteristic features of microsomal fatty acid desaturases including the three histidine boxes HXXXH, HXXHH, and QXXHH (these domains may contain the active site and/or be involved in metal ion binding), and the N-terminal cytochrome b5 domain containing the heme-binding motif, HPGG, similar to that of other fatty acid desaturases. Belongs to the fatty acid desaturase type 1 family.