Effects of Environmental Stressors on the Hematological Indices of Some Freshwater Teleosts

Nellie Lopez


Changes in blood values were observed in young adult freshwater fishes exposed to environmental stressors. Clarias batrachus (TL=221-391 mm; 68.7-371.4 g) starved for 34, 47 and 53 days showed significant reductions in lymphocyte counts. Lymphocyte percentages decreased while neutrophil percentages increased in starved fish. Oreochromis niloticus (TL=105-172 mm; 19.1-77.6 g) exposed for 30 days to 10 and 20 ppm ZnSO4 concentrations at pH 6.7-7.2 showed consistent reductions in total WBC and lymphocyte counts but insignificant changes in RBC-related values. O. niloticus (TL=56-124 mm; 4.0-21.7 g) exposed for 96 h to 10, 20, and 30 ppm ZnSO4 concentrations showed a general tendency of reduction in RBC-reIated values and total and relative WBC counts.

Exposure of O. niloticus (TL=56-106mm; 2.9-14.2 g) for 96 h to 5, 10, and 20 ppm ZnSO4 at low ph (ph 3.1-3.8) elicited marked increases in neutrophil counts and reductions in lymphocyte and RBC counts. O. niloticus (TL=94-154 mm; 13.2-54.4 g) subjected to 24 h and 48 h crowding showed increased hematocrit, neutrophilia, and lymphopenia. In Ophicephalus striatus (TL=259-306 mm; 123.2-192.8 g) stressful effects of crowding and handling were less evident from the blood values obtained after 24 hand 48 h exposure.

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