2.8. Lysozyme Activity Assay. Plasma lysozyme activity was
measured using the method of Ellis [18] with some modifications.
Briefly, a volume of 0.02% (w/v) suspension of
Micrococcus lysodeikticus ATCC No. 4698 (Sigma-Aldrich)
prepared in 0.05M phosphate buffer (pH 6.2) was used as
a substrate. Lyophilized hen egg white lysozyme (Sigma-
Aldrich) was used as a standard.One hundredmL of standard
solutions and fish plasma were added to a 3mL suspension
of M. lysodeikticus. After incubation for 5min at 25∘C, the
absorbance of the mixtures was examined at the wavelength
of 550 nm. The lysozyme activity of fish plasma was reported
as mg/mL equivalent of hen egg white lysozyme activity.