Abstract:
Fish parasites such as cestodes are regarded as good bioindicators of environmental contamination with trace elements including heavy metals. Research on their biondicative potentials in Lake Naivasha, Kenya is lacking. This study aimed to determine the levels of selected heavy metals Arsenic (As), Chromium (Cr), Lead (Pb) and Mercury (Hg) in the straightfin barb (Enteromius paludinosus) and its endo-parasites as bioindicators in Lake Naivasha, Kenya. Water, sediment and 1307 fish were collected from November 2017 to February 2018. The fish were transported to the laboratory in the Department of Biological Sciences, Egerton University. In the laboratory, their lengths and weights were then measured followed by dissection to examine their gonads, obtain the muscle tissues and the parasites. The samples were analyzed for heavy metals using a Thermal-electron atomic absorption spectrophotometer at the Lake Nakuru Water Quality and Testing Laboratory. The equations for the length-weight relationship of the combined sexes, males and females of E. paludinosus were, log W = 3.23 log L + log 0.11, log W = 2.83 log L + log 0.15 and log W = 2.87 log L + log 0.15 respectively. The mean condition factor of the combined sex, males and females were; 0.59, 0.57 and 0.60 respectively. The sex ratio of the fish samples was 1: 1.98 (males: females). The concentrations of heavy metals in the water sample was 0.076 and 0.001 mg/l for Pb and Hg respectively while that of As and Cr were below detection limit. The concentrations of heavy metals in the sediment were 0.17, 1.49, 15.82 and 0.05 mg/kg wet weight for As, Cr, Pb and Hg respectively. In the muscle tissues of the fish, the mean concentrations of As, Cr, Pb and Hg were 5.07, 22.09, 45.21 and 1.55 mg/kg ww respectively. The bioaccumulation factors for L. intestinalis were 2.41, 2.19, 5.86 and 5.14 for As, Cr, Pb and Hg, respectively. It was concluded that the population of E. paludinosus in Lake Naivasha had a good growth ratio but not in a good condition. Therefore, it is recommended that further analysis of length-weight relationship and condition factor should be carried out for both dry and wet seasons. This study also concludes that the fish are not safe for consumption. This is because of the health risks that could be brought about by the high levels of Pb and Hg in the fish muscle tissue that both exceeded the FAO/WHO and EU maximum permissible limits. Additionally, the cestode, L. intestinalis showed a potential of accumulating heavy metal levels from the fish host (E. paludinosus). Because of that, it is recommended that more studies should be done on other cestodes and acanthocephalans that infect different fish species in Lake Naivasha. This will aid in establishing their bioindicative potentials in addition to L. intestinalis
