| dc.description.abstract | Heavy metals have been recognised to be a major source of pollution in the aquatic
ecosystems. Lates niloticus and its caridina nilotica feed, was selected as bioindicators
because of their abundance in the gulf of Winam and their predator - prey relationship.
The heavy metals determination was done by the x-ray fluorescence (XRF) analytical
technique. For quality control Atomic Absorption Spectrophotometry (AAS) was also
used for some samples. The analytical method was validated using International Atomic
Energy Agency (IAEA) certified reference material MA-A-2 (Fish homogenate) on both
the two techniques. The results agreed within acceptable range.
The fish samples were collected within a period of six months with the bulk collected
during a 10 day cruise aboard RV Utafiti on a trip sponsored by Lake Victoria
Environmental Programme (LVEMP). A total of about 100 individuals of Lates niloticus
and several caridina nilotica were collected from the Winam gulf of Lake Victoria. Prior
to analysis the samples were digested in an aluminum block available at Kenya Marine
and Fisheries Research Institute (K.M.F.R.I) laboratory in Kisumu and preconcentrated.
The results of the study showed that the values obtained for Pb, Zn, Ni, Cu, Fe, and
Mn were within the CAC and WHO guidelines. In the muscle tissue the heavy metals
concentration levels ranged as follows: Pb, 0.1- 0.4 ug g"; Zn, 3.3- 5.9 ug g"; Ni, 0.1 -
0.6 Ilg g"; Cu, 0.2- 0.91lg g': Fe, 2.2 - 20.21lg g-l and Mn, 0.3 - 1.11lg g'. The results
also showed a distinct variability in heavy metals in the different tissues of Lates
niloticus. Liver presented the highest levels of iron with a mean of 41.21lg g-l and a
range of 6.3 - 96.01lg g-l. Muscle tissue had substantial mean concentration of iron with a
mean of 5.61lg s' and a range of2.2 - 20.2 ug g-l.
III
In terms of bioaccumulation of iron amongst the Lates niloticus tissues the order
in descending order is as follows; Liver> Skin> Muscle tissue> Gills> Scales. Analysis
of data showed a positive correlation (r = 0.61) between the concentration of heavy
metals in caridina niloticus and Lates niloticus. This was expected since Caridina
niloticus forms the bulk of Lates niloticus feed. Analysis of variance indicated that there
is a significant variations in the heavy metal concentration in Lates niloticus tissues at p 0.05 significance level. Canonical correspondence analysis showed distinct variability in
the elemental concentrations in Lates niloticus tissues and organs.
Conductivity measurements of water results varied significantly from as low as
112 ms at the Mbita course way to 156 ms at the Asembo Bay. This indicated the
difference in anthropogenic inputs across the Winam gulf of lake Victoria. | en |
