The present study investigated the hematological indices of Oreochromis niloticus (Nile tilapia) from Kalgwai Dam, Hadejia, Jigawa State, Nigeria,for the period of twenty-four months (24) with a focus on assessing the health status of the fish population in relation to potential environmental stressors and parasitic infections. Moreover, as a result of an array of some devastating activities which include illegal fishing, nomadic farming, washing of clothes, and other households’ belongings, using detergents, however, reaches of the dam, serve as refuse dump site, which is increasing pollution influx into the dam. Haematological indices count such as Packed cell volume (PCV), Red blood cell (RBC), Haemoglobin (Hb), Mean corpuscular volume (MCV), Mean corpuscular haemoglobin (MCH), Mean corpuscular haemoglobin content (MCHC), White blood cell (WBC), Neutrophils, Lymphocytes, Monocyte, Basophils and Eosinophils were measured using standard laboratory procedures. The mean value recorded for PCV. were 15.00 % to 34.50%, RBC were 1.35±0.21to 2.70±0.28, (Hb) were 6.50 g/dL to 11.50 g/dL, mean of MCV, MCH and MCHC ranged from 26.00±14.14 to 61.00±28, 34.50±16.26 to 52.50±17.68 and 24.50±9.19 to 49.00±7.07 for MCV, MCH and MCHC respectively. WBC were 120.00±28.28 to 230.50±57.28, Neutrophils ranged from 33.50±14.85 to 56.00±21.21, Lymphocytes were34.00±12.73 to 61.50±27.58. Moreover, 0% was recorded for Monocytes, Basophils and Eosinophils. The observed variations in hematological parameters are indicative of sample fish health conditions, potentially linked to water quality issues or parasite prevalence in the dam. This study underscores the importance of regular monitoring of hematological indices as bioindicators of fish health, which can serve as an early warning system for ecological disturbances and the presence of disease-causing agents in aquatic ecosystems.
Keywords: Hematological indices, Oreochromis niloticus, Kalgwai Dam, parasitic infection, environmental stress, fish health, Nigeria.