2.7.1. Plasma alternative haemolytic complement pathway(ACH500, lysozyme and peroxidase activities ACH50 was determined following the method described by Sunyer and Tort[471, using rabbit red blood cells(RaRBC) as target cells to haemolysis. The serially diluted plasma was incubated(100 min) with RaRBC(2.8 x 108 cell ml-1), centrifuged(122 x g. 2.5 min) and the optical density(OD) of the supernatant was measured at 414 nm. The reciprocal of the serum dilution causing lysis of RaRBC was designated as ACH50 l48l. Results are 50% presented as ACH50 units mL Lysozyme activity was determined in plasma and skin mucus measuring(450 nm) the decrease of the turbidity of a Micrococcus lysodeikticus suspension, as described by Ellis 19l and Hutchinson and Manning 1501. Lysozyme concentration(Hg mL was esti mated using lyophilized hen egg-white lysozyme(Sigma serially diluted in sodium phosphate buffer(0.05 M: pH 6.2) to establish a standard curve. Skin mucus was prepared according methodology adapted from Fagan et al. 151 l and Fast et al. 152 After sequential centrifugation 1500 x g, 20 000 x g, for 10 min at 4 oC) the su pernatants were diluted with 3 parts of sodium phosphate buffer 0.05 M: pH 6.2) and analysed as previous described. Total peroxidase activity in plasma was measured as described by Quade and Roth 153. The peroxidase activity(U mL plasma) was determined assuming that one unit of peroxidase produces an absorbance change of 1 oD. All analyses were conducted in triplicates