2.2. Sampling procedures
The fish were euthanized with 0.04% 2-phenoxyethanol, weighed
and measured and their fork length was measured. Blood was collected
via caudal puncture using non-heparinised 5 ml syringes then
transferred to 3 ml tubes on ice. Fish were then grossly examined
and the presence of parasites on the skin, gills and operculum
recorded. Gills were removed and placed into seawater Davidson's
fixative. Blood samples stored at 4 °C overnight, centrifuged at
800 ×g for 5 min and serum removed and stored at −80 °C. Gills
were transferred to 70% ethanol after 24 h fixation.
2.3. Serum osmolality and lysozyme activity
Serum osmolality (mmol·kg−1) was measured using a Vapro©
Model 5520 vapour pressure osmometer (Wescor Inc., Logan, Utah,
USA) from 10 μL of serum and each sample measured in duplicate. Lysozyme
activity was measured using a method based on that described
by Carrington and Secombes (2007).