Histopathological Effects Of Acutely Toxic Levels Of Palm Oil Mill Effluent On Gill And Liver Of Nile Tilapia Fingerlings

Abstract

The toxicity of Palm Oil Mill Effluent (POME) was investigated with emphasis on histopathological effects of Nile Tilapia (Oreochromis niloticus) juvenile. Static bioassay was conducted to determine the LC50 of POME to Nile tilapia fingerlings. The fishes were exposed to 0, 5, 25, 50 mg/l of POME. Histopathological examinations were performed on the gills and liver of Nile tilapia fingerlings exposed to POME under standard laboratory condition. 120 live and apparently healthy O. niloticus fingerlings measuring 9.3-10.6cm standard length and weighed between 5.8g and 6.5g were randomly distributed into twelve (40cm x 29cm x 28cm) glass tanks of 60 litres capacity each were filled with 20litres aerated unchlorinated well water at ten fish/tank for the experiment. The toxicant was introduced at different concentrations in duplicate per treatment. The lethal concentration (LC50) value of POME was 9.19mg/l for 96h of exposure. The total mortality occurred in the concentration of 50mg/litre within 24hours of exposure period. Toxic reactions exhibited by the fish include erratic movement, air gulping, loss of reflex, molting, barbell deformation, hemorrhage and excessive mucus secretion in fish exposed to higher concentration of POME. Histopathology of the organs after 96 hr exposure revealed cell proliferation, lamellar fusion, lamellar cell hyperplasia, and epithelial lifting. In the liver, there was vacuolation of hepatocytes and necrosis. The changes in these tissues occur predominantly in the 96 hr exposure. Respiratory stress, erratic swimming and instant death of fish were observed in exposed fish, which varied with the concentration of the toxicant. Histopathological examination of the gills and liver of Nile tilapia fingerlings showed varied degrees of degenerative changes including vacuolation and necrosis which worsened with increasing concentration of the effluent. Observations on the bioassay test indicated hyper exetability and the eagerness of the test fish to jump out of the pollutant. This is a confirmation that fish in river Oluwa where Palm Oil Mill Effluent had been discharged into over decades must have either migrated out of the zones or died due to POME toxicity. POME is highly toxic to Oreochromis niloticus, therefore it’s discharged directly into water bodies, near fish farms or in areas close to aquatic bodies should not be encouraged.

Index Terms— necrosis Palm oil mill effluent, River Oluwa, toxicity, histopathological