Comparison of differential leukocyte counts in fish of economic and indicator importance

Abstract

The aim of this study was to determine the percentage of individual types of leukocytes in fish of economic (carp - Cyprinus carpio L., tench - Tinca tinca L., European catfish - Silurus glanis L., rainbow trout - Oncorhynchus mykiss Walb.,) and indicator importance (bream - Abramis brama L., perch - Perca fluviatilis L., chub - Leuciscus cephalus L., brown trout - Salmo trutta m. fario L.). In all, we examined 191 fish specimens caught in non-contaminated or insignificantly contaminated localities in good state of health during the vegetation season and not within the season of their reproduction. Leukocytes stained according to Giemsa were classified as: lymphocytes, monocytes, myelocytes, metamyelocytes, neutrophilic granulocytes with band and segmented nuclei, eosinophils and basophils. Blood of all the fish species examined was of lymphocytic character. The mean percentage of individual lymphocytes varied from 84.2 ± 5.08 to 99.1 ± 0.99%. The lowest percentage of lymphocytes was found in the rainbow and brown trout (84.2±5.08 and 87.3±7.21%, respectively), while the highest values were in the perch (99.1±0.99 and 97.5±3.19%). Monocytes were sporadic in all the fish species; with the highest mean value found in the female spawner European catfish (1.42 ± 1.74%. The highest percentage of granulocytic series cells was found in rainbow (15.4 ± 7.80%) and brown trout (11.6 ± 7.23%); whereas the lowest values in the perch (0.8 ± 1.01 and 2.4 ± 3.15%). As far as the granulocytic series cells are concerned, metamyelocytes were most common with regards to their percentage in all the fish species excepting salmonids. There were prevailing band and segmented neutrophils in the rainbow and brown trout. Granulocytes were mostly represented by neutrophils in all the fish species studied. Eosinophilic granulocytes were found sporadically in the tench (0.17 ± 0.59%) and in 3-year old carp (0.10±0.19%). Basophilic granulocytes were not found in any of the fish species examined. We found practically equal percentage of individual types of leukocytes in the carp, bream and perch of various age categories caught under the same conditions and in the same season of the year. There were no significant differences in the percentage of individual leukocytes in male and female spawners of 3-year-old carp, 3-year-old tench, and 2- to 3-year-old brown trout. Our results contribute to the use and help in introducing the examination of differential leukocyte counts as a biological monitoring method to evaluate surface water contamination.