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 ef fects of Nile Tilapia ( Oreochromis niloticus ) juvenile. Static bioassay was conducted to determine the LC 50 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 gill s and liver of Nile tilap ia fingerlings exposed to POME under standard laboratory condition. 120 live and apparently healthy O. niloticus fingerling s 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 f ish/tank for the e xperiment. The toxicant was introduced at different concentrations in duplicate per treatment . The lethal concentration (LC 50 ) 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, barb ell deformation, hemorrha ge and excessive mucus secretion in fish exposed to higher concentration of POME. Histopathology of the or gans after 96 hr exposure revealed cell proliferation, lamellar fusion, lamellar cell hyperplasia, and epithelial lifting. In the liver, there was vacu olation of hepatocytes and necrosis. The changes in these tissues occur predominantly in the 96 hr exposu re. Respiratory stress, erratic swimming and instant death of fish were observed in exposed fish, which varied with the concentratio n of the toxicant. Histopathological examination of the gills and liver of Nile tilapia fingerlings showed varied degre es of degenerative changes including vacuolation and necrosis which worsened with increasing concentration of the effluent. Obs ervations 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 o ut of the zones or died d ue to POME toxicity. POME is highly toxic to Oreochromis niloticus , therefore it’s discharged direc tly into water bodies, near fish farms or in areas close to aquatic bodies should not be encouraged