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¹ Faculty of Oceanography, University of Calabar, Calabar, Nigeria DOI : 10.4194/2618-6381-v20_1_07 Viewed : 3933 - Downloaded : 1944 Parachanna obscura commands high food value and quite critical in the control of tilapia population in ponds. The health status of fish is assured upon proper diagnosis of the blood parameters. Research on fifty P. obscura from Great Kwa River, Nigeria investigated, showed 24 (48%) were infested with nematode and infected the blood while 26 (52%) were not. The mean blood Pack cell volume (PCV), Lymphocyte, Monocyte, Leucocyte, Neutrophils, and Eosinophils for infected(non-infested) P. obscura respectively were 20.8% (21.6%); 44.4% (39.3%); 1.9% (1.92%); 4.18x103mm- 3(4.48x103mm-3), 51.7% (57.5%). and 1.58% (1.2%). No positive correlation existed between infested and non-infested. The lower PCV, Leucocyte, and Neutrophils are indications of lower immunity. Prevalence rate increased with size from 26% (22- 26.9cm), 56.5% (27-31.9cm) to 66.7% at class range 32-36.9cm, while Incidence of infestation decreased with increase in length, 2.75, 2.25 and 2.0 respectively for 22- 26.9cm, 27-31.9cm and 32-36.9cm. The class 12-16.9cm did not follow any pattern. The parasitic burden occurred at the weaker/more vulnerable part-anal pore (61.7%), followed by fish intestine (29.8%), cardiac (4.3%) and caecum (4.3%). The mean physicochemical parameters of the study area across the three tidal intervals ranged from 5.11±0.04-6.72±0.00 for pH, conductivity 18.70±0.20µS-37.95±1.05 µS, dissolved oxygen 2.60±0.00 mg/l- 4.00±0.60 mg/l, temperature 25.50±0.50°C-27.00±0.00°C, salinity 0.01±0.00mg/l-0.03±0.01mg/l and total dissolved solid (TDS) 23.19±0.25mg/l- 47.06±1.30mg/l. Keywords : P. obscura, Prevalence, Haematology, Aquaculture, Nematode, Fish healt