CHANGES IN PLASMA LYSOZYME AND BLOOD LEUKOCYTE LEVELS OF HATCHERY-REARED ATLANTIC SALMON (SALMO-SALAR L) AND SEA TROUT (SALMO-TRUTTA L) DURING PARR SMOLT TRANSFORMATION

Changes in gill (Na+-K+)-ATPase, plasma lysozyme activities, and blood leucocyte levels of hatchery-reared salmon, Salmo salar L. (1- and 2-year-old) and sea trout, Salmo trutta L. (2-year-old) were monitored during the parr-smolt transformation. Temperature-dependent variation was observed during the winter months between fish reared at ambient water temperature and fish acclimated to 10-degrees-C. Marked decreases in plasma lysozyme activity, blood total leucocyte and lymphocyte numbers of salmon were observed during smoltification. In sea trout these decreases took place in February and March. Changes in the plasma lysozyme level of trout coincided to some degree with changes in the number of circulating neutrophils. Differences observed between salmon and sea trout can be assigned partly to different smoltification patterns in these species.