The impact of UDN on selected blood parameters of female sea trout Salmo trutta m. trutta (L.) spawners

Blood tests were performed on 150 females sea trouts Salmo trutta m. trutta L. during four spawning seasons (2014-2017). Fish were caught on a Polish Angling Association trapping point, the Słupia River, Słupsk (northern Poland). The blood for analysis was drawn from caudal vein of 56 healthy and 94 UDN (Ulcerative Dermal Necrosis) - infected females. Fish were divided into three groups: (1) healthy, with no visible signs of UDN, (2) sick, with up to 10% skin damage and (3) agonal, where more than 10% of body surface was infected. Statistically important decrease in red blood cell count (RBC), hemoglobin concentration (HGB) and hematocrit (HCT) were found between sick and agonal fish groups. Concentration of total plasma protein and albumin decreased, in relation to fish health deterioration. Blood urea nitrogen (BUN) had an inverse proportionality to total plasma protein and albumin concentration. Based on decrease of RBC, HGB and HCT due to UDN symptoms development a decrease in fish condition was observed. Significantly higher urea concentrations observed in agonal fish may indicates respiratory and excretory systems failure.