Recovery rate, haematological parameters and growth responses of Heterobranchus longifilis exposed to zinc oxide nanoparticles

The present study investigated the toxicity effects of zinc oxide nano-particles (ZnO-NPs) on haematological parameters and growth responses of Heterobranchus longifilis. Catfish juveniles were exposed to sub-lethal concentrations (0.00, 6.00, 8.00, 10.00 and 12.00 mg/l) of zinc oxide nano-particles in static renewal bioassays for 60 days. The ZnO-NPs-exposed fish were then subjected to depuration phase for 30 days to monitor the recovery ability of the fish. After each experimental stage, fish were sacrificed and blood was collected for haematological variables such as: erythrocytes {Red blood cells (RBC), packed cell volume (PCV) and haemoglobin (HB)} and leucocytes {White blood cells (WBC), platelets (PLT), lymphocyte (LYMPH) and neutrophil (NEUT)} using standard procedure. Results revealed reduction (p < 0.05) in the values of RBC counts (0.70 x 106 /µl) in 10.00 and 12.00mg/l ZnO-NPs treated fish when compared to control group (3.70 x 106 /µl). A reverse trend was observed with significantly (p < 0.05) high WBC counts (220.70 x 103 /µl) in group treated with the highest concentration (12.00mg/l) of ZnO-NPs after 60 days of exposure. The recovery experiment followed a different trend with a gradual decrease in RBC values from 2.2 x 106 /µl in 6.00mg/l to 2.00 x 106 /µl in 12.00mg/l while WBC counts increased from 182.00 x 103 /µl in 6.00 mg/l to 194.30 x 103 /µl in 12.00mg/l. The highest percentage weight gain (58%) was recorded in the control group with the lowest (26%) in the ZnO-NPs-exposed group. However, fish growth increased as the depuration period increased. The results of this findings indicated that ZnO-NPs may have some adverse effects on the physiology of H. longifilis, however, the fish showed some ability to recover from the effects over time. Keywords: Depuration, Haematology, Heterobranchus longifilis, ZnO-NPs