Nucleotide composition suggests MT-CYB gene is AT rich and C/A ending codons are more preferred in pisces, aves and mammals.

Mean value of ENC was high which indicates low codon usage bias but CAI value was high suggesting high expression of CYB gene vertebrates.

Nonsignificant correlation between ENC and CAI suggests that nucleotide composition has very weak relationship with codon selection.

Correlation coefficient between codon usage and GC3 was positive suggesting that GC ending codons positively influenced the GC3 content.

Correspondence analysis (COA) suggests that both mutation pressure and natural selection affect the codon usage in CYB gene.