Longer-Term Adverse Effects of Selenate Exposures on Hematological and Serum Biochemical Variables in Air-Breathing Fish Channa punctata (Bloch, 1973) and Non-air Breathing Fish Ctenopharyngodon Idella (Cuvier, 1844): an Integrated Biomarker Response Approach

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Abstract
To examine the spectrum of selenium toxicity between hardy and less hardy species of the same life stages, short-term and longer-term exposures in juvenile air-breathing fish Channa punctata (Bloch, 1973) and non-air-breathing fish Ctenopharyngodon idella (Cuvier, 1844) were assessed. Acute exposures revealed a greater 96-h median lethal concentration (LC50) for C. punctata (14.67 mg/l) compared to C. idella (7.98 mg/l). During their chronic exposure, both fishes’ hemoglobin content (Hb), red blood cells (RBC), and hematocrit (HCT) markedly decreased (p < 0.05), although their clotting time (CT) significantly increased. At 96 h, immune-modulation was observed where total protein and serum globulin levels in both fishes considerably decreased (p < 0.05) compared to the first exposure at 0 days, although total glucose, triglyceride, cholesterol, and albumin levels in both fishes significantly increased (p < 0.05) at 30 days. The lower cholesterol levels in C. punctata compared to C. idella are suggestive of a disrupted cholesterol transformation pathway. The greater total protein, triglyceride, albumin, and globulin levels in C. punctata compared to C. idella are suggestive of a comparatively robust immune capacity. In essence, selenium toxicity in the wild could manifest as disrupted metabolic pathways and downregulated immune capacity for less hardy species. In general, both fish species displayed significant alterations in their hematological and biochemical responses with increased exposure duration and elevated toxicant concentrations. This comparative investigation could improve the knowledge-spectrum of selenium toxicity in the wild as well as an understanding of secondary stress responses critically evident in hematological and biochemical parameters.

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