USE OF FISH BIOMARKERS TO ASSESS MICRO- POLLUTANT EXPOSURE AND EFFECTS IN LAKE KANYABOLI, KENYA

Abstract

A lot of research in ecotoxicology is currently focused on identifying and developing suitable biomarkers for use in assessing environmental pollution. This study, set out to evaluate the use of a suite of biomarkers in Clarias gariepinus in assessing micro-pollutant exposure and effects in Lake Kanyaboli from November 2013 to April 2014. Fish were collected with the aid of a gill net of mesh size 4” and 5” whereas bottom sediment was collected by ErkMan crab sampler. The concentrations of Cadmium, Chromium, Zinc, Copper, and Lead in lake sediment and in the liver of Clarias gariepinus were determined using Flame Atomic Absorption Spectrophotometry (AAS). A necropsy-based health assessment index (HAI), the condition factor, hepatosomatic index (HSI), and splenosomatic index (SSI) were measured in fish from all the sampling stations. Fish were semi-quantitatively sampled from which an organ index was calculated to examine the micro- pollutant exposure and effects in fish from all the study stations. Metals concentrations were significantly (Fα, v1, v2 = 7.16; p < 0.05) higher in station 2 than at the other stations. The mean heavy metal concentration in Clarias gariepinus liver were Cd (nd-0.22±0.01), Cr (0.37 ± 0.01 - 1.67 ± 0.03), Zn (7.12 ± 0.03 - 13.40 ± 0.32), Cu (2.12 ± 0.12 - 4.16 ± 0.12) and Pb (1.63 ± 0.33 - 14.40 ± 0.58). Zn exhibited a significance difference between the stations (Fα, v1, v2 = 7.79; p < 0.05). Redundancy ordination analysis (RDA) revealed positive linear relation between heavy metals in sediments and fish liver except for Zinc concentration in sediments and fish liver which showed a negative relationship. The mean of the biomarkers were HAI (20.61 ± 1.01 - 47.43 ± 1.12), Condition factor (0.60 ± 0.03 - 0.91 ± 0.29), HSI (0.53 ± 0.03 - 0.67 ± 0.03), SSI (0.08 ± 0.00 - 0.12 ± 0.01) and Semi-quantitative histological assessment index (8.3 ± 0.41 - 17.63 ± 0.36). The multivariate analysis of the histology – based fish health assessment index (HBFHAI) showed that these biomarkers are being influenced by the concentration of heavy metals in sediments as well as fish liver and therefore qualified as biomarkers for assessing pollutant exposure and effects. It is concluded that histology-based fish health assessment index biomarkers can be used to assess the health of aquatic organisms and ecological health of Lake Kanyaboli and other aquatic habitats within the Lake Victoria Basin. However, a more comprehensive chemical analysis of water and sediments samples including the measurements of endocrine disrupting chemicals is recommended for future studies to further investigate possible causative agents regarding liver alterations identified.