Discipline: Veterinary Medicine
A total of 40 catfish (Clarias gariepinus) were exposed for 96 h to natural BOD (biological oxygen demand) levels of the wastewater treatment lagoons of swine farm (control lagoon, 1.3 mg/L; lagoon 1, 719 ± 94 mg/L; lagoon 2, 190 mg/L; lagoon 3, 57 ±19 mg/L). After exposure, the gills, liver, spleen and kidney were examined and scored for lesions. Gill alterations included congestion, hemorrhage, basal cell hyperplasia, fusion of secondary lamellae and necrosis. Gill lesions were found to be highest in fishes exposed to the highest BOD level, which produced 100% mortality within 14 h. The lesions appeared to be consistent with that of acute tissue response to hypoxic and toxic conditions. Few to no lesions were observed in the gills of fish exposed to lower BOD levels. The liver of fishes at the highest BOD level showed congestion, hemorrhage, fatty degeneration, cloudy swelling, increased granularity of the cytoplasm and necrosis. Lower BOD levels on the other hand, elicited less severe cellular changes. The kidney and spleen showed considerable changes at the highest BOD level. In the kidney, congestion, hemorrhage, vacuolation and necrosis were observed whereas necrosis and an increase in the number and size of melanomacrophage centers were found in the spleen. Results of the study revealed an increasing lesion score with the rise in the BOD level which is suggestive of the deleterious effects of high BOD levels on these organs.